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Meteorology

Meteorology

Welcome to the Meteorology section. All questions and answers are unverified regarding correctness. Please report any errors in our Pilot Forum.

  • Volcanic ash encounters…
  • What is the biggest hazard in heavy rain on final approach?
  • What causes saturation?
  • Visibility Definitions….
  • What causes greatest change in Altimeter, Air Speed, and Rate of Climb?
  • What kind of ice does freezing rain cause?
  • At what temp does structural icing occur?
  • What weather conditions form frost?
  • Define wind shear…
  • What is mechanical turbulence?
  • What is convective instability?
  • What weather conditions form tornadoes?
  • Order of precedence when flying around thunderstorm
  • Know requirements for thunderstorm development…
  • What are the worst hazards of squall lines or thunderstorms?
  • What are the general conditions of occlusions?
  • Describe the two types of occlusions
  • Three parts of air mass classification
  • Temp relationship with air and land
  • Define air mass
  • What are the three types of stability?
  • What are the 4 lifting actions and their differences?
  • Two types of weather conditions that cause icing
  • Difference between relative humidity and specific humidity
  • Humidity definitions…
  • What two forces cause winds to travel parallel to isobars?
  • What kinds of drifts are associated with a high-pressure area?
  • What 3 elements are associated with moisture?
  • Define the tropopause…
  • Where can Rime Ice occur?
  • What is Rime Ice?
  • Where does clear ice occur?
  • When will clear ice normally occur at?
  • What happens to ice formation with an increase in airspeed?
  • What factors affect the rate of ice accumulation on an aircraft?
  • When may freezing rain be encountered?
  • When may structural ice form?
  • What are the three requirements for the formation of icing?
  • How does Wet Snow Form?
  • What is super cooled water?
  • What are the cumulative effects of icing?
  • One rule for Turbulent Flight:
  • Discuss Wind Shear Turbulence.
  • What are the rules that should be applied when mountain wave turbulence has been forecasted?
  • Where is the extreme turbulence found when near mountains?
  • What are rotor clouds, cap clods, and Lenticular Clouds?
  • What does the strength and magnitude of Mechanical Turbulence Depend on?
  • How does Mechanical turbulence Work?
  • What is the worst thermal?
  • How does Thermal Turbulence Work?
  • How can Turbulence be divided up?
  • What are the reporting term definitions?
  • What are the four intensities of turbulence?
  • Discuss actions within a storm
  • How should Thunderstorms be avoided?
  • What are some good cues about microbursts coming from departure and arrival reports?
  • What are the best sources of information?
  • How does a LLWAS work?
  • What are the four methods of detection, and the three wind shear alert systems used?
  • What are the visual cues for a microburst?
  • How long does a microburst last?
  • What are the hazards associated with Thunderstorms?
  • What happens to pressure when a storm approaches?
  • What are the basic requirements for a formation of a thunderstorm?
  • What sort of weather is associated with occluded fronts?
  • What does the widespread precipitation area ahead of a warm front often result in?
  • What is some extreme weather conditions associated with squall lines?
  • What does the extent of cloudiness in cold air depend on?
  • Discuss pressures with relation to fronts.
  • How do you locate and classify fronts?
  • Describe Maritime Tropical Cold Air as they move over the ground.
  • What happens with air with high moisture content?
  • Describe air masses flowing over ground, with heating and cooling.
  • Describe Maritime and Continental fronts.
  • What is an adiabatic process?
  • Describe Lifted Air…
  • Nimbostratus….
  • Stratus
  • Cumulonimbus
  • What are the types of precipitation?
  • What is Dew Point Depression?
  • What is Dew Point Temperature?
  • What is Specific Humidity?
  • Explain Land Breeze.
  • Explain Sea Breeze.
  • How does something get classified as a Jet Stream?
  • What is Buys Ballot’s Law?
  • Given a gradient wind calculate a surface wind.
  • What does surface friction do to the wind speed? How does this affect the Coriolis force?
  • What direction and altitude do gradient winds flow?
  • Define Pressure Gradient
  • What are the factors that influence actual circulation?
  • What is circulation, and how is it created?
  • How does air temperature relate to indicated altimeter reading?
  • What are the pressure rules?
  • What is Density Altitude, and how is it found?
  • What is pressure altitude?
  • What happens when in between isobars, especially when they are close together?
  • What is Sea Level Pressure?
  • What does pressure do with an increase in altitude?
  • Define an inversion.
  • Define Lapse Rate. What is a steep, shallow, and isothermal lapse rate?
  • What is the horizontal transfer of heat? How is this normally accomplished?
  • What is Convection?
  • What is Conduction?
  • What is the process by which energy is transferred through space in the form of electromagnetic waves?
  • Define insolation.
  • What are the six primary flight hazards?
  • What are the six weather elements?
  • What is the percentage by volume of water vapour in the atmosphere?
  • What Is the Stratosphere?
  • What is the tropopause? Why is this “boundary” significant?
  • What happens to the atmosphere with altitude? Where does most of the weight of the atmosphere reside?
  • The definitions of the alerts and the order in which
  • Micro burst alerts and severe turbulence alerts
  • Windshear and Turbulence Warning System [WTWS]
  • If encountering windshear, what is the recovery technique?
  • Explain windshear in a microburst.
  • What do you know about windshear?
  • What causes a microburst?
  • What do you know about Microbursts?
  • What action would you take if you encountered CAT?
  • Where are you most likely to encounter Clear Air Turbulence [CAT]?
  • What is Clear Air Turbulence [CAT]?
  • What do you know about Jet streams?
  • Which way does the earth turn about its axis? [Draw on whiteboard]
  • Draw a picture of the earth on a white board.
  • What does windshear do, what is your procedure if you
  • There is a thunderstorm on final, what do you think about?
  • What are the standard, the dry and the saturated adiabatic lapse rates?
  • What is the Inter-Tropical Convergence Zone?
  • Tell me about the Monsoon.
  • Tell me about a cold front.
  • Tell me about a warm front.
  • Can a typhoon/cyclone cross the equator?
  • Which direction do they travel?
  • Which way do they turn?
  • Where do Typhoons form?
  • What do you know about tropical cyclones/hurricanes (typhoons)?
  • What is the value of the Coriolis parameter, at the equator?
  • What is Coriolis parameter?
  • What is the ICAO standard atmosphere?
  • Volcanic ash encounters. What do you know about it?
  • What is the biggest hazard in heavy rain on final approach?
  • What causes saturation?
  • Here are some visibility definitions…
  • What causes greatest change in Altimeter, Air Speed, and Rate of Climb?
  • What kind of ice does freezing rain cause?
  • At what temp does structural icing occur?
  • What weather conditions form frost?
  • Define wind shear…
  • What is mechanical turbulence?
  • What is convective instability?
  • What weather conditions form tornadoes?
  • What is the order of precedence when flying around thunderstorm
  • What does it require for a thunderstorm to develop?
  • What are the worst hazards of squall lines or thunderstorms?
  • What are the general conditions of occlusions?
  • Describe the two types of occlusions…
  • Describe the three parts of air mass classification…
  • What is the temp. relationship between air and land?
  • Define air mass…
  • What are the three types of stability?
  • What are the 4 lifting actions and their differences?
  • The two types of weather conditions that cause icing are…
  • What is the difference between relative humidity and specific humidity?
  • Humidity definitions…
  • What two forces cause winds to travel parallel to isobars?
  • What kinds of drifts are associated with a high-pressure area?
  • What 3 elements are associated with moisture?
  • Define the tropopause…
  • Where can Rime Ice occur?
  • What is Rime Ice?
  • Where does clear ice occur?
  • When will clear ice normally occur at?
  • What happens to ice formation with an increase in airspeed?
  • What factors affect the rate of ice accumulation on an aircraft?
  • When may freezing rain be encountered?
  • When may structural ice form?
  • What are the three requirements for the formation of icing?
  • How does Wet Snow Form?
  • What is super cooled water?
  • What are the cumulative effects of icing?
  • How do you fly the aircraft in turbulent weather?
  • Discuss Wind Shear Turbulence.
  • What are the rules that should be applied when mountain wave turbulence has been forecasted?
  • Where is the extreme turbulence found when near mountains?
  • What are rotor clouds, cap clods, and Lenticular Clouds?
  • What does the strength and magnitude of Mechanical Turbulence Depend on?
  • How does Mechanical turbulence Work?
  • What is the worst thermal?
  • How does Thermal Turbulence Work?
  • How can Turbulence be divided up?
  • What are the reporting term definitions?
  • What are the four intensities of turbulence?
  • Discuss actions within a storm.
  • How should Thunderstorms be avoided?
  • What are some good cues about microbursts coming from departure and arrival reports?
  • What are the best sources of information?
  • How does a LLWAS work?
  • What are the four methods of detection, and the three wind shear alert systems used?
  • What are the visual cues for a microburst?
  • How long does a microburst last?
  • What are the hazards associated with Thunderstorms?
  • What happens to pressure when a storm approaches?
  • What are the basic requirements for a formation of a thunderstorm?
  • What sort of weather is associated with occluded fronts?
  • What does the widespread precipitation area ahead of a warm front often result in?
  • What is some extreme weather conditions associated with squall lines?
  • What does the extent of cloudiness in cold air depend on?
  • Discuss pressures with relation to fronts.
  • How do you locate and classify fronts?
  • Describe Maritime Tropical Cold Air as they move over the ground.
  • What happens with air with high moisture content?
  • Describe air masses flowing over ground, with heating and cooling.
  • Describe Maritime and Continental fronts.
  • What is an adiabatic process?
  • Describe Lifted Air….
  • What is a nimbostratus cloud?
  • What can you tell us about stratus clouds
  • What can you tell us about CB’s?
  • What are the types of precipitation?
  • What is Dew Point Depression?
  • What is Dew Point Temperature?
  • What is Specific Humidity?
  • Explain Land Breeze.
  • Explain Sea Breeze.
  • How does something get classified as a Jet Stream?
  • What is Buys Ballot’s Law?
  • Given a gradient wind, calculate a surface wind.
  • What does surface friction do to the wind speed?
  • What direction and altitude do gradient winds flow?
  • Define Pressure Gradient
  • What are the factors that influence actual circulation?
  • What is circulation, and how is it created?
  • How does air temperature relate to indicated altimeter reading?
  • What are the pressure rules?
  • What is Density Altitude, and how is it found?
  • What is pressure altitude?
  • What happens when in between isobars, especially when they are close together?
  • What is Sea Level Pressure?
  • What does pressure do with an increase in altitude?
  • Define an inversion.
  • Define Lapse Rate. What is a steep, shallow, and isothermal lapse rate?
  • What is the horizontal transfer of heat? How is this normally accomplished?
  • What is Convection?
  • What is Conduction?
  • What is the process by which energy is transferred through space in the form of electromagnetic waves?
  • Define insolation.
  • What are the six primary flight hazards?
  • What are the six weather elements?
  • What is the percentage by volume of water vapour in the atmosphere?
  • What Is the Stratosphere?
  • What is the tropopause? Why is this “boundary” significant?
  • What happens to the atmosphere with altitude? Where does most of the weight of the atmosphere reside?
  • What causes fog?
  • Micro burst alerts and severe turbulence alerts. What do you know about it?
  • Ever heard about a Windshear and Turbulence Warning System [WTWS]
  • If encountering windshear, what is the recovery technique?
  • Explain windshear in a microburst.
  • What do you know about windshear?
  • What causes a microburst?
  • What do you know about Microbursts?
  • What action would you take if you encountered CAT?
  • Where are you most likely to encounter Clear Air Turbulence [CAT]?
  • What is Clear Air Turbulence [CAT]?
  • What do you know about Jet streams?
  • Which way does the earth turn about its axis?
  • What does windshear do, what is your procedure if you encounter one?
  • There is a thunderstorm on final, what do you think about?
  • What are the standard, the dry and the saturated adiabatic lapse rates?
  • What is the Inter-Tropical Convergence Zone?
  • Tell me about the Monsoon.
  • Tell me about a cold front.
  • Tell me about a warm front.
  • Can a typhoon/cyclone cross the equator?
  • Which direction do they travel?
  • Which way do they turn?
  • Where do Typhoons form?
  • What do you know about tropical cyclones/hurricanes (typhoons)?
  • What is the value of the Coriolis parameter, at the equator?
  • What is Coriolis parameter?
  • What is the ICAO standard atmosphere?
Volcanic ash encounters…

Despite ongoing avoidance efforts, operators can still experience volcanic ash encounters. Guidance on the operational issues surrounding volcanic ash is divided into three aspects: avoidance, recognition, and procedures. The following information is general; flight crews should refer to their respective company’s operating manuals for details.

Avoidance
Preventing flight into potential ash environments requires planning in these areas: Dispatch needs to provide flight crews with information about volcanic events, such as potentially eruptive volcanoes and known ash sightings, that could affect a particular route.

Dispatch also needs to identify alternate routes to help flight crews avoid airspace containing volcanic ash. Flight crews should stay upwind of volcanic ash and dust. Flight crews should note that airborne weather radar is ineffective for distinguishing ash and small dust particles.

Recognition
Indicators that an airplane is penetrating volcanic ash are related to odour, haze, changing engine conditions, airspeed, pressurization, and static discharges.

Odour
When encountering a volcanic ash cloud, flight crews usually notice a smoky or acrid odour that can smell like electrical smoke, burned dust, or sulphur.

Haze
Most flight crews, as well as cabin crew or passengers, see a haze develop within the airplane. Dust can settle on surfaces.

Changing engine conditions
Surging, torching from the tailpipe, and flameouts can occur. Engine temperatures can change unexpectedly, and a white glow can appear at the engine inlet.

Airspeed
If volcanic ash fouls the Pitot tube, the indicated airspeed can decrease or fluctuate erratically.

Pressurization
Cabin pressure can change, including possible loss of cabin pressurization.

Static discharges
A phenomenon similar to St. Elmo’s fire or glow can occur. In these instances, blue-coloured sparks can appear to flow up the outside of the windshield or a white glow can appear at the leading edges of the wings or at the front of the engine inlets.

Procedures
The following nine procedures are general recommendations. Each operator’s flight operations manuals will include more specific directions.

Reduce thrust to idle immediately By reducing thrust, engines may suffer less build-up of molten debris on turbine blades and hot-section components. Idle thrust allows engines to continue producing electrical power, bleed air for pressurization, and hydraulic power for airplane control.

Turn the auto throttles off
This prevents the engines from increasing thrust above idle. Ash debris in the engine can result in reduced surge margins, and limiting the number of thrust adjustments improves the chances of engine recovery.

Exit the ash cloud as quickly as possible
A 180-deg turn out of the ash cloud using a descending turn is the quickest exit strategy. Many ash clouds extend for hundreds of miles, so assuming that the encounter will end shortly can be false. Climbing out of the ash could result in increased engine debris build-up as the result of increased temperatures. The increased engine build-up can cause total thrust loss.

Turn on engine and wing anti-ice devices and all air-conditioning packs
These actions improve the engine stall margins by increasing the flow of bleed air.

If possible, start the auxiliary power unit [APU]
The APU can power systems in the event of a multiple-engine power loss. It can also be used to restart engines through the use of APU bleed air.

If volcanic dust fills the flight deck, the crew may need to use oxygen
Use flight deck oxygen at the 100 percent setting. Manual deployment of the passenger oxygen system is not required because it will deploy automatically if the cabin altitude exceeds 14,000 ft.

Turn on the continuous ignition
Confirm that auto start is on, if available. In the event that the engines flame out or stall, use appropriate procedures to restart the engines. During restart, the engines may take longer than normal to reach idle thrust due to the combined effects of high altitude and volcanic ash ingestion. If an engine fails to start, try restarting it again immediately. Flight crews should remember that the airplane may be out of the air start envelope if the encounter occurs during cruise.

Monitor engine exhaust gas temperature (EGT)
Because of potential engine debris build-up, the EGT can climb excessively. The flight crew should prevent EGT accedences. Shut down the engine and restart it if the EGT is approaching limits similar to a hung start.

Fly the airplane by monitoring airspeed and pitch attitude
If necessary, follow the procedure for flight with unreliable airspeed.

What is the biggest hazard in heavy rain on final approach?

Reduced visibility
Possible windshear

What causes saturation?

  • Cooling temp to dew point
  • Evaporations brings dew point to temp [adds moisture to air]
Visibility Definitions….

Visibility: the ability to see prominent unlighted objects by day and prominent lighted objects by night, expressed in nm.

Flight visibility: average forward horizontal distance measured in nm from the cockpit in flight

Prevailing visibility: greatest forward horizontal visibility, SM, equal or exceeded throughout at least half of the horizon circle, which need not be continuous

Runway Visual Range: horizontal distance a pilot will see by looking down the runway from the approach end

Slant Range visibility: distance on final approach when you can see the runway Obscuring Phenomena: any collection of particles, which will reduce horizontal visibility

Ceiling: height AGL to the lowest broken or overcast layer, or the vertical visibility into obscuring phenomena

Vertical visibility: distance seen directly upward from the ground level into obscuring phenomena

What causes greatest change in Altimeter, Air Speed, and Rate of Climb?

Icing is greater than pressure
Affects are due to Pitot-Static clogs

What kind of ice does freezing rain cause?

Clear ice…

At what temp does structural icing occur?

Below 0ºC

What weather conditions form frost?

  • Little or no wind
  • Lack of clouds
  • OAT below freezing
  • Dew point within 5ºC of air temp
Define wind shear…

Sudden change in wind direction and or speed over a short distance.

What is mechanical turbulence?

Any irregular terrain. Mountains, buildings, trees

What is convective instability?

Dry air over Moist – Moist air over Dry

What weather conditions form tornadoes?

  • Marked convective instability
  • Pronounced horizontal wind shear
  • Rapid moving cold fronts or squall lines
  • Strong convergence
Order of precedence when flying around thunderstorm

  • Go around
  • Fly over the top
  • Fly below
  • Fly through the lower 1/3
Know requirements for thunderstorm development…

Lifting [most likely convergence]
Unstable air
Moisture content in the air
Building clouds through the freezing level

What are the worst hazards of squall lines or thunderstorms?

Primary: Turbulence
Secondary: Hail

What are the general conditions of occlusions?

Combination of warm and cold fronts

Describe the two types of occlusions

Occlusions have three air masses and two fronts.
Left side is behind, right side is ahead.

Three parts of air mass classification

First is source region. [Arctic, Polar, Tropical, Equatorial]
Second is surface of their source region. [Maritime or Continental]
Third is temp [cold or warm]

Temp relationship with air and land

Air temp is relative to surface below it
Summer time, air masses are cold
Winter air masses are warm

Define air mass

A large body of air that has essentially uniform temperature and moisture conditions, in a horizontal plan.

What are the three types of stability?

Stable: Air is pushed up until lifting action is removed, air is colder than the surrounding air, so it falls to its original position

Unstable: Air is pushed up until lifting action is removed, air is warmer than the surrounding air, so it is pushed up and continues to rise

Neutral: Air is pushed up until lifting action is removed, air is the same temp as the surrounding air and therefore it remains in place

 

Flight Conditions Stable Atmosphere Unstable Atmosphere
Cloud type Stratus Cumulus
Turbulence Smooth Rough
Visibility Poor Good (outside cloud)
Winds Steady Gusty
Precipitation Steady Showery
Icing Rime Clear
Air Mass Warm Cold
Front Warm Cold

 

What are the 4 lifting actions and their differences?

  • Convergence: winds meet, cause air to move vertically
  • Orographic: wind runs into terrain, so it is lifted
  • Frontal: front moves in, air is pushed up
  • Thermal: sun heats land, land gives off heat, warm air rises
Two types of weather conditions that cause icing

Supercooled water [freezing rain]
Wet snow

Difference between relative humidity and specific humidity

Relative Humidity measures the percent of saturated air or what percentage of the bucket is filled with water.

Specific Humidity measures how much water vapour is contained per unit mass of air or how much water is in the bucket.

Humidity definitions…

Relative Humidity: percentage of saturated air
Specific Humidity: Ratio of water vapour per unit mass of air. The higher the dew point the higher the specific humidity.

What two forces cause winds to travel parallel to isobars?

  • Coriolis Force: bends gradient winds to the right, do not affect surface wind because of friction
  • Pressure Gradient Force: initiating force for all winds
What kinds of drifts are associated with a high-pressure area?

High-pressure area, winds flow clockwise. Fly into a high, you get right cross wind and left drift.

What 3 elements are associated with moisture?

Clouds
Humidity
Precipitation

Define the tropopause…

  • Transition zone between the troposphere and the stratosphere
  • Temperature is isothermal with altitude
  • An abrupt change in rate of temperature decrease with increasing altitude marks this boundary
  • It’s a region not a layer
Where can Rime Ice occur?

Rime ice can be expected in stratiform clouds since vertical currents are not strong enough to support large droplets.

What is Rime Ice?

Rime ice is a milky white, opaque, and granular deposit of ice formed through the rapid freezing of small super-cooled water droplets. Rime ice is most likely to occur at temperatures of –10 to –20.

Where does clear ice occur?

Clear ice occurs in cumuliform clouds with appropriate temperatures where vertical currents can support large drops.

When will clear ice normally occur at?

Clear ice normally occurs at temperatures between 0C and –10C in, but may occur with temperatures as cold as –25. Clear icing is the most severe form of icing.

What happens to ice formation with an increase in airspeed?

As airspeed is increased more water is encountered over a given period of time and therefore the rate of deposit is increased.

What factors affect the rate of ice accumulation on an aircraft?

The following items affect the rate of ice accumulation on an aircraft:

The size and number of water drops in a given volume of air, airfoil thickness, and airspeed.

Since thick airfoils have a larger deflective force they collect ice more slowly than thin airfoils, which have a smaller deflective force. Droplet size also is a factor. Smaller drops have a greater tendency to follow the air stream and larger droplets resist this deflecting force.

When may freezing rain be encountered?

Freezing rain or drizzle may be encountered in the clear air below a cloud layer.

When may structural ice form?

Structural Ice may form when the free-air temperature is 0C or colder.

What are the three requirements for the formation of icing?

There three requirements for the formation of structural icing are as follows: Outside air temperature below freezing, aircraft skin temperature below freezing, and visible moisture.

How does Wet Snow Form?

Wet Snow occurs at temperatures just below freezing and can come about as the result of turbulence in the air and the resulting mixture of super cooled moisture.

What is super cooled water?

Super Cooled water is liquid water found at air temperatures below freezing. Super cooled water droplets are numerous in clouds at temperatures between 0C and –15C with decreasing amounts at colder temperatures.

What are the cumulative effects of icing?

Lift decreases, weight increases, Drag increases, Thrust Decreases, Fuel consumption increases, and stall speed increases.

One rule for Turbulent Flight:

Trim the aircraft for level flight at the recommended turbulent air penetration airspeed. Severe turbulence may cause large and rapid variations in indicated airspeed. Don’t chase airspeed.

Discuss Wind Shear Turbulence.

Wind Shear Turbulence is defined as a sudden change in wind direction and or speed over a short distance. The greater the change in wind speed and/or direction in a given direction, the more severe the turbulence. These turbulent wind shear flight conditions are frequently encountered in the vicinity of the jet stream where large shears in both the horizontal and vertical planes are found as well as I association with land and sea breezes, fronts, inversions, and thunderstorms.

What are the rules that should be applied when mountain wave turbulence has been forecasted?

  • Avoid the turbulence if possible by flying around the areas where wave conditions exist. If this is not feasible, fly at a level that is at least 50% higher than the height of the highest mountain range along your flight path. This procedure will now keep the aircraft out of turbulence, but provides a margin of safety if a strong downdraft is encountered.
  • Avoid the rotor, lenticular, and cap clouds since they contain intense turbulence and strong updrafts and down drafts.
  • Approach the mountain range at a 45-degree angle, so that a quick turn can be made away from the ridge if a severe downdraft is encountered.
  • Do not place too much confidence in your pressure altimeter reading near mountain peaks. They may indicate altitudes, which are more than 2500 feet higher than your true altitude.
  • Penetrate turbulent areas at air speeds recommended for your aircraft.
Where is the extreme turbulence found when near mountains?

Severe turbulence can be frequently found from the surface to the tropopause and 150 miles downwind when the winds are greater than 50 knots at the mountaintop. Extreme turbulence is usually found at low levels on the leeward side of the mountain in or near the rotor and cap clouds when the winds are 50 knots or greater at the mountaintop. Moderate turbulence often can be experienced out to 300 miles under the previously stated conditions.

What are rotor clouds, cap clods, and Lenticular Clouds?

The rotor clouds forms at a lower level and is generally found at about the same height as the mountain ridge. The cap cloud usually obscures both sides of the mountain peak. The lenticular clouds like the rotor and cap clouds are stationary in position.

What does the strength and magnitude of Mechanical Turbulence Depend on?

The strength and magnitude of mechanical turbulence depends on the speed of the wind, the roughness of the terrain, and the stability of the air.

How does Mechanical turbulence Work?

When the air near the surface of the earth flows over obstructions, such as irregular terrain, or buildings, the normal horizontal wind flow is disturbed and transformed into a complicated pattern of eddies and other irregular air movements.

What is the worst thermal?

A ploughed field

How does Thermal Turbulence Work?

Vertical air movements resulting from convective currents develop in air, which is heated by contact with a warm surface. This heating from below occurs when either cold air is moved over a warmer surface, or the ground is strongly heated by solar radiation.

How can Turbulence be divided up?

Types of Turbulence can be divided according to causative factors: Thermal, mechanical, frontal, large-scale wind shear.

What are the reporting term definitions?

Occasional: Less then 1/3 of the time.
Intermittent: 1/3 to 2/3rds of the time.
Continuous: More than 2/3rds of the time.

What are the four intensities of turbulence?

Light, Moderate, Severe, Extreme

Discuss actions within a storm

Once inside the storm, the pilot should let the plane ride out the updrafts and downdrafts and concentrate on maintaining a level attitude. With power set to maintain the proper airspeed, maintaining the same attitude will result in only minor airspeed variations. However, the aircraft’s altitude may vary by thousands of feet. The rapidly changing pressure conditions within the storm will result in unreliable indications and erratic variations in altitude, airspeed, and rate of climb instruments. Since the attitude gyro is independent of the Pitot-static system, its indications should be considered reliable.

How should Thunderstorms be avoided?

Fly around them
Fly over the top of the storm
Fly below the storm
If not possible to avoid the storm, fly through the lower 1/3 of the storm

What are some good cues about microbursts coming from departure and arrival reports?

Departure or arrival weather reports calling for gusty winds, heavy rain, or thunderstorms should be a clue that a high potential for microburst activity exists.

What are the best sources of information?

PIREPS [Pilot Reports] and Weather Alerts are one of the best sources of information.

How does a LLWAS work?

For example, the Low Level Winds Shear Alert System [LLWAS] Measures the winds speed and direction at several points on the ground and compares them with a reference sensor located near the centre of the airfield.

What are the four methods of detection, and the three wind shear alert systems used?

4 methods of detection:

  • Visual PIREPS, and weather reports
  • Wind shear alert systems
  • Doppler radar
  • and LLWAS
What are the visual cues for a microburst?

Visual clues include virga, localized blowing dust, rain shafts with rain diverging away from the core of the cell, roll clouds, and of course and indication of vivid lightning or tornado-like activity.

How long does a microburst last?

A microburst normally lasts from five to ten minutes after its diverging wind flow first hits the earth’s surface.

What are the hazards associated with Thunderstorms?

Thunderstorms are accompanies by some or all of the following hazards: extreme turbulence, hail, microburst, icing, lighting, and tornadoes. Turbulence and hail are the greatest hazards and are found in the upper 2/3rds of a mature stage cell.

What happens to pressure when a storm approaches?

Large pressure changes can accompany thunderstorm formation.

What are the basic requirements for a formation of a thunderstorm?

The basic requirements for the formation of a thunderstorm [Cumulonimbus cloud] are as follows: lifting action, unstable air, high moisture content, and a cloud building through the freezing level.

What sort of weather is associated with occluded fronts?

Since the occluded front is the result of meeting of a cold front and a warm front, the weather associated with the occlusion will be a combination of both types of frontal weather. If an occlusion is approaching from the east, you would first encounter warm front type weather which may extend for several hundred miles to the east of the surface front. On the other hand, if it were approached from the wet you would first encounter cold front type weather.

What does the widespread precipitation area ahead of a warm front often result in?

The widespread precipitation area ahead of a typical warm front often results in low stratus and the formation of fog.

What is some extreme weather conditions associated with squall lines?

Squall lines contain severe weather conditions including the following: extreme turbulence, heavy rain, lightning, icing, and frequently hail, and/or tornadoes.

What does the extent of cloudiness in cold air depend on?

The extent of the cloudiness in the cold air depends on the degree of stability and moisture content of the cold air mass.

Discuss pressures with relation to fronts.

All fronts are located in troughs of low pressure and the lowest pressure will extend from the low centre along this trough. Therefore, when a front approaches a station, or a pilot flies toward a front, the pressure decreases. Pressure normally rises immediately following frontal passage. Because of this pressure change, it is extremely important to obtain a new altimeter setting the vicinity of a front.

How do you locate and classify fronts?

Differences in the various properties of adjacent air masses, such as temperature, moisture, wind, and pressure are used to locate and classify fronts.

Describe Maritime Tropical Cold Air as they move over the ground.

By the afternoon, these often build into towering cumulus and cumulonimbus clouds resulting in scattered rain showers and thunderstorms.

What happens with air with high moisture content?

Due to the high moisture content of the air (Tropical Warm), condensation may result in fog, low stratus, steady precipitation, or any combination of these.

Describe air masses flowing over ground, with heating and cooling.

If the air mass is warmer than the surface, it is cooled by contact with the cold ground, becomes more stable, and is called a warm air mass. If the air mass is colder than the surface over which it is moving, it is heated from below, resulting in convective currents and instability, and is called a cold air mass.

Describe Maritime and Continental fronts.

Maritime has high moisture content, Continental has Low.

What is an adiabatic process?

An adiabatic process occurs when the temperature of a body of air changes without heat being added or taken away. When a parcel of air is lifted in the atmosphere, it expands due to decreasing pressure.

Describe Lifted Air…

Lifted air that is colder than the surrounding air settles when the lifting action is removed since it is denser. This indicates a stable condition. Lifted air that is warmer than the surround air continues to rise when the lifting action is removed because it is less dense indicates an unstable condition.

Nimbostratus….

Nimbostratus clouds are dark massive cloud layers having a wet appearance and accompanied by heavy steady precipitation such as rain or snow. This cloud is classified as a middle cloud.

Stratus

Form in layers with smooth bases and tops. They are grey in appearance when viewed from the surface, and often cover the entire sky. The stable air that gives stratus clouds their layered characteristics also inhibits the vertical spread of smoke, dust and haze particles and thus tends to lower visibility. Precipitation, when occurring, is generally light steady rain or drizzle. Stratus clouds are generally associated with smooth flight conditions.

Cumulonimbus

Large, dense towering clouds with cauliflower-like tops. The top portion of the cloud is often flattened into an anvil shape or consists of cirrus formation resulting from ice crystals. Water droplets form the major portion of the cloud, but ice crystals appear in the upper portions. Cumulonimbus and thunderstorm are synonymous terms; they result in strong winds, lightning, and intermittent heavy showery precipitation. The well-developed cumulonimbus may be the parent of the hailstorm.

What are the types of precipitation?

Drizzle, freezing drizzle, rain, freezing rain, hail, ice pellets, snow grains, snow.

What is Dew Point Depression?

Dew Point depression is the difference, in degrees, between the air temperature and the dew point temperature. [When air temp equals dew point temp, saturation occurs].

What is Dew Point Temperature?

The temperature at which saturation occurs. It is also the temperature where moisture first starts to condense on exposed surfaces forming dew. Dew point is an indication of, and is directly related to, specific humidity.

What is Specific Humidity?

Specific humidity is the ratio of water vapour per unit mass of air, and is expressed as grams of water per kilogram of air. For a particular temperature, there is a maximum specific humidity, or maximum amount of water vapour that the air can hold. The higher the temperature, the more water vapour the air can hold.

Explain Land Breeze.

At night, the circulation is reversed so that the air movement is from land to sea, producing an offshore wind called the land breeze.

Explain Sea Breeze.

During the day, the pressure over the warm land becomes lower than that over the colder water. The cool air over the water moves toward the lower pressure, forcing the warm air over land upward. The resulting onshore wind is called a sea breeze. Sea breezes of 15 to 20 knots are not uncommon.

How does something get classified as a Jet Stream?

To be classified as a jet, it is generally accepted that the winds must be 50 knots or greater and the core, area of maximum wind, must possess considerable length.

What is Buys Ballot’s Law?

This law states that if the wind is at your back, the area of lower pressure will be to your left.

Given a gradient wind calculate a surface wind.

Subtract 45 degrees.

What does surface friction do to the wind speed? How does this affect the Coriolis force?

Surface friction reduces the speed of the wind. Since magnitude of Coriolis force varies with the speed of wind, a reduction in the wind speed by friction causes a reduction in the Coriolis force.

What direction and altitude do gradient winds flow?

Gradient winds flow parallel to the isobars and above 2000 AGL. Note: PGF and Coriolis force cause gradient winds to travel parallel to the isobars.

Define Pressure Gradient

The rate of change in pressure with horizontal distance between a high and low-pressure area is called pressure gradient. Large differences in pressure between horizontal points result in stronger pressure gradient forces. This Pressure gradient force is the initiating force for all winds. Close spacing of isobars indicates greater pressure gradients and higher wind speeds.

What are the factors that influence actual circulation?

This circulation is modified considerably by:

  • The irregular distribution of oceans and continents
  • The relative effectiveness of differing surfaces in transferring heat to the atmosphere Irregular terrain
  • Daily variations in temperature
  • The changes of seasons
  • And many other factors
What is circulation, and how is it created?

Circulation is the recurring movement of air relative to the earth’s surface. It is created primarily by the large temperature difference between the tropics and the Polar Regions, and complicated by uneven heating of the land and water areas by the sun.

How does air temperature relate to indicated altimeter reading?

If the air is colder than the standard atmosphere, the aircraft will be lower than the altimeter indicates. If the air is warmer than standard, the aircraft will be higher than the altimeter indicates.

What are the pressure rules?

High to low, look out below
Low to high, plenty of sky

What is Density Altitude, and how is it found?

Density altitude is the altitude in the standard atmosphere what has the same density as the local air. It is found by correcting the pressure altitude for non-standard temperature deviations.

What is pressure altitude?

Pressure altitude is the height above the standard datum plane of 1013Hpa when above 10,000 ft in Australia.

What happens when in between isobars, especially when they are close together?

The rate of pressure change in a direction perpendicular to the isobars (horizontal distance) is called the pressure gradient. The gradient is steep, or strong, when the isobars are close together, and is shallow, or weak, when the isobars are far apart. Pressure gradient is the initiating force for all winds.

What is Sea Level Pressure?

Sea Level Pressure (SLP) is the pressure at mean sea level (MSL), measured directly at sea level or calculated if the station is not at sea level. Station pressure is the atmospheric pressure at an airfield or station.

What does pressure do with an increase in altitude?

Pressure, unlike temperature, always decreases with altitude.

Define an inversion.

An Inversion [inverted lapse rate] occurs when the temperature increases with an increase in altitude.

Define Lapse Rate. What is a steep, shallow, and isothermal lapse rate?

The change in atmospheric temperature with increasing altitude is called a lapse rate. The average or standard lapse rate is 2ºC per 1000′. If the temperature decreases very rapidly with altitude [greater than 3 Celsius], it is called a steep lapse rate. When the temperature decreases very gradually [Between 1.5 and 3] it is called a shallow lapse rate, while no change with altitude is called an isothermal lapse rate.

What is the horizontal transfer of heat? How is this normally accomplished?

Advection is the horizontal transfer of heat, normally by wind.

What is Convection?

Convection is the vertical transfer of heat.

What is Conduction?

Conduction is the transfer of heat from molecule to molecule by contact and it accounts for the transfer of heat between the earth’s surface and the adjacent air.

What is the process by which energy is transferred through space in the form of electromagnetic waves?

Radiation is the process by which energy is transferred through space in the form of electromagnetic waves.

Define insolation.

Insolation is the total radiation reaching the earth’s surface and it is the primary source for all weather phenomena on the earth.

What are the six primary flight hazards?

The six primary flight hazards are turbulence, thunderstorms, wind shear, icing, low ceilings, and low visibility.

What are the six weather elements?

Weather, as a broad subject, is often classified as being composed of six weather elements: Temperature, atmospheric pressure, wind, humidity, clouds, and precipitation. The last three are all associated with moisture.

What is the percentage by volume of water vapour in the atmosphere?

The atmosphere also contains water vapour amounting to 0% to 5% by volume.

What Is the Stratosphere?

The stratosphere is characterized by increasing temperature with increasing altitude.

What is the tropopause? Why is this “boundary” significant?

An abrupt change in the rate of temperature decrease with increasing altitude marks the boundary, called the tropopause.

What happens to the atmosphere with altitude? Where does most of the weight of the atmosphere reside?

The atmosphere becomes less dense with altitude, and roughly 50% of it, by weight, lies below 18,000 ft, and 90 % within 53,000 feet. Within the troposphere, the temperature normally decreases with increasing altitude.

The definitions of the alerts and the order in which

Fog forms when the relative humidity reaches 100%, and the air temperature tries to drop below the dewpoint, causing the water vapour to condense. Fog is cloud in contact with the ground. It can form in a number of ways, depending on how the cooling that caused the condensation occurred:

Radiation fog is formed by the cooling of land after sunset by thermal [infrared] radiation in calm conditions with clear sky. The cool ground then produces condensation in the nearby air by conduction. In perfect calm the fog layer can be less than a metre deep but turbulence can promote a thicker layer [wind of 2-8kts will deepen the fog]. Radiation fog is generally associated with a high-pressure system and will usually not persist long past sunrise.

Advection fog occurs when moist air passes over cool ground by advection [wind] and is cooled. This form is most common at sea when tropical air encounters cooler higher-latitude waters. It is also extremely common as a warm front passes over an area with significant snow pack.

Micro burst alerts and severe turbulence alerts

The definitions of the alerts and the order in which they are prioritised is as follows:

TDWR Microburst Alert (MBA*) [Loss of 30 knots or greater]
Terrain-Induced (TIWT*) [Windshear-loss of 30 knots or greater]
Terrain-Induced (TIWT) [Windshear-gain of 30 knots or greater]
Terrain-Induced (TIWT) [Severe Turbulence]
TDWR Windshear Alert (WSA*) [loss or gain of 15 to 30 kts]
Terrain-Induced (TIWT) [Windshear-loss or gain of 15 to 30kts]
Terrain-Induced (TIWT)

Moderate Turbulence:
No Alert

* MBA [Microburst Alert]
* TIWT [Terrain induced Windshear and turbulence]
* WSA [Windshear Alert]

Windshear and Turbulence Warning System [WTWS]

Hong Kong’s Chek Lap Kok Airport [VHHH] is located on partly reclaimed land adjacent to Lantau Island, whose rugged terrain has a maximum elevation of nearly 3,280’. Consequently, aircraft operating at the new airport may be affected by significant terrain-induced windshear and turbulence under certain meteorological conditions.

In order to enhance safety and operational efficiency at the airport, an operational Windshear and Turbulence Warning System [WTWS] developed by a company called Weather Information Technologies Inc. [WITI] was introduced. This system provides alerts for terrain- and convective-induced windshear and turbulence and has been utilized by air traffic controllers and pilots since the airport’s opening day, 6 July 1998.

In addition to providing real-time windshear and turbulence alerts to controllers and pilots, the system provides up to 12-hour forecasts of terminal area turbulence to aviation meteorologists. The WTWS was previously known as the OWWS – the Operational Windshear Warning System. To utilize this system efficiently, it is important that pilots understand how this system was developed, what it can do and what its limitations are.

Prior to the development of the windshear warning system, several studies were conducted in Hong Kong to gain an insight into the meteorological conditions near the location of the new airport. These studies included analysis of routine weather observations, special observing programs and meteorological modelling of the differences between the old Kai Tak Airport and at Chek Lap Kok. Variables analysed included wind direction and speed, temperature, clouds, visibility, rainfall, thunderstorms and fog. Methods used to conduct these studies included investigative flights by light aircraft and water tank and wind tunnel experiments. The 44-month project was under the sponsorship of the Hong Kong Observatory. The WTWS development team included WITI, the National Centre for Atmospheric Research (NCAR), Hong Kong University of Science and Technology [HKUST], and the University of Wyoming.

Components include basic and applied research on wind flow over Hong Kong’s terrain; a scientific field study, warning system concept and feasibility studies, system design, development, testing, implementation and training. The WTWS provides real-time hazardous weather information to air traffic controllers and pilots to enhance safety in the terminal area and improve predictions of hazardous weather to support strategic decision making by air traffic managers. The WTWS is the first system worldwide to provide real-time alerts of terrain-induced turbulence and alerts for both convective and terrain-induced windshear, The WTWS also provides predictions of turbulence caused by terrain and airport surface wind as well as numerical weather prediction guidance. For detection of convective windshear, the WTWS relies partly on the output from a Raytheon developed Terminal Doppler Weather Radar [TDWR] at Tai Lam Chung, about 12 kilometres from Chek Lap Kok. The windshear warning system analyses TDWR signatures including gust front, precipitation intensity, and storm motion, providing an integrated alert system. It generates graphics and text designed for easy interpretation by pilots, controllers, traffic managers and aviation forecasters.

Terminal Doppler Weather Radar [TDWR]
The Terminal Doppler Weather Radar [TDWR] is proven technology and uses Doppler shift to detect convective windshear. It is already in operational use at Denver, USA, and other airports, but this will be the first time it is being used in a coastal environment with busy marine traffic.

The design criterion is for a probability of detection [POD] of 90% and a false alarm rate [FAR] of 10%. [In the USA, PODs of 95% and FARs of 3% have been achieved]. The output products are shown on a geographical situation display [GSD] and on the alphanumeric alert displays [AAD] at the air traffic controllers’ stations.

The primary WTWS product suite includes detection of terrain-induced turbulence, terrain-induced windshear, convective microburst and windshear, gust fronts, precipitation intensity and storm motion. It also predicts terrain-induced turbulence and airport surface wind and numerical weather prediction guidance. Pilots, controllers, air traffic managers and aviation forecasters easily interpret the graphical and text formats. The alerts use commonly accepted aeronautical navigation terminology. The WTWS graphic display delivers hazardous weather warning information and other meteorological products. It shows the horizontal profile of various hazardous weather areas, vertical wind profiles near the approach and departure corridors, and textual warning messages. Video replay of the recent product history is possible. The meteorological situation is displayed in several user-selectable ranges and levels of detail. Critical products and important situation changes are highlighted visually on the display and/or announced by audible signals.

User needs were established over a two-year period culminating in a prototype demonstration in October 1995. As a result of comments by users, the system was designed to provide high performance, distinguish between the phenomena of windshear and turbulence, use existing aeronautical terminology and provide spatial extent of the phenomena as well as up to 12-hour forecasts of surface wind and turbulence at a 30-minute resolution.

Alerts had to be reserved for significant events and assigned a priority. They also had to be concise but informative and provided within three nautical miles of runways. Products had to support both tactical and strategic decision-making and be updated fast enough to cover operations that occur every two minutes. The alphanumeric alarm display is designed to alert controllers to time-critical weather hazards and to provide textual warnings for communication to pilots. Alerts are given as microburst, windshear or turbulence, with associated intensity and location. For windshear and microburst alerts, intensity is given as headwind “loss” or “gain” in knots; for turbulence, intensity is specified as “moderate” or “severe”. The intensity is the maximum expected along the alert corridor and the alert location is where the event is first expected to be encountered.

Event locations for windshear alerts are given as one, two or three nautical miles on approach or departure – or on the runway. Event locations for turbulence alerts are identified as departure or approach. It was originally planned that the easterly runways [07R/L] would be the preferred runways, but it has now been suggested that it may be better to use the westerly runways whenever possible. The main reason for this change is to minimise traffic confliction with the Macau and Shenzhen airports and to overcome the problems of vectoring aircraft within Hong Kong airspace. It is too early to assess whether this may also alleviate the effects of the terrain-induced turbulence, but this is being studied at this time. It should be noted that the prevailing wind in Hong Kong is easterly.

In the summer, strong southerly winds, sometimes associated with typhoons, are present on occasions, but otherwise light winds flow from that direction. In autumn and winter, the north-easterly monsoon affects the area. It follows that during normal conditions, when operating from runways 25L/R, there will be a slight tailwind and a crosswind. The runways are approximately 3800m long and there are lesser obstacle problems to the west, so the tailwind should not be a critical factor. [The rapid exits have also been located to cater for the various different landing weights, including those specifically for fully laden cargo aircraft.]

Aircraft are positioned at approximately 15nm for 25R, which is the preferential landing runway. Pilots are able to listen to alerts being given to proceeding aircraft, which help to build up a picture of the conditions on short finals. The situation on 07R/L is not so straightforward because of the proximity of Macau and the airspace boundary. This means that aircraft are not transferred to tower control until about 7nm and so pilots will only normally hear their own specific warning.

If encountering windshear, what is the recovery technique?

  • Disconnect the autopilot
  • Aggressively apply max power/thrust Roll wings level, unless terrain is a factor, to maximize aircraft performance
  • Pitch up, rotating at a normal takeoff rotation rate [2-3°/sec] to max body angle [15-17º] or until stick-shaker
  • Verify speed brakes are retracted
  • Do not alter gear/flap configuration until terrain clearance is assured [adverse effects to stall] Issue Pilot report [PIREP]
Explain windshear in a microburst.

↑ Airspeed
↓ Airspeed [rapid]
↑ Rate of descent

What do you know about windshear?

Windshear may be caused by a number of meteorological phenomenon including temperature inversions, sea breezes, frontal systems, strong surface winds and thunderstorms. Windshear is any rapid change in wind direction or velocity. Severe windshear is a rapid change in wind direction or velocity causing airspeed changes greater than 15 knots or vertical speed changes greater than 500 feet per minute.

Light: Minor excursions from flight path or speed
Moderate: Significant effect on control of the aircraft
Strong: Difficulty in keeping aircraft on desired flight path and or speed
Severe: Hazardous effects to aircraft controllability

What causes a microburst?

A microburst will usually be associated with strong updrafts. If there is virga associated with a CB, it occurs due to the preceding convective action raising the air to the saturation level, that is, the parcel of air cooled as it ascended, could no longer hold the moisture in it, it then condensed to form cloud, then coalesced to form precipitation, and started to descend in the from of rain. If there is a wind aloft, the descending air will be adjacent to the rising air. When the air below the rain is dry, the water evaporates, and forms virga. When evaporation takes place, cooling takes place through the release of latent heat. Resulting in a parcel of cool air, which already descending, begins to descend even faster.

A microburst may be dry – or wet. Those below virga are considered dry, and those in a rain shaft are considered wet microbursts. Depending on the winds aloft, a dry microburst could be in the clouds just above you and to the side of your flight path, especially if you are flying adjacent to a thunderstorm, and you will never even see it develop.

Observations suggest that approximately five percent of all thunderstorms produce a microburst.

What do you know about Microbursts?

A microburst is a strong downdraft of air, up to 6,000 ft/min [60kts], which seldom lasts more than 15-20 minutes and is typically less than one mile wide. To put it into perspective, lift at 1,000 FPM is actually 10 kts of wind in the vertical axis. As the parcel nears the ground at around 1,000 to 3,000 ft, it begins to change to a horizontal flow, creating a wind near the surface as high as 45 kts.

Microbursts occur near developing thunderstorms, or CB clouds. Some visual cues to watch for include – abnormally strong lift, unusual rain patterns, virga, blowing dust on the surface, a localized heavy rain shaft, with light winds reported on the surface, high temperature and low dew point.

What action would you take if you encountered CAT?

Adjust speed to turbulence penetration speed encountering the first moderate bumps or before if CAT has been forecast or known to exist on track. Doing so will avoid structural damage to the airplane through overstressing the airframe.

Where are you most likely to encounter Clear Air Turbulence [CAT]?

The most likely place to expect Clear Air Turbulence [CAT] is just above the central core of the jet stream near the polar tropopause and just below the core. Clear air turbulence does not occur in the core. CAT is encountered more frequently in winter when the jet stream winds are strongest. Nevertheless, CAT is not always present in the jet stream and, because it is random and transient in nature, it is almost impossible to forecast.

Clear air turbulence may be associated with other weather patterns, especially in wind shear associated with the sharply curved contours of strong lows, troughs and ridges aloft, at or below the tropopause, and in areas of strong cold or warm air advection. Mountain waves create severe CAT that may extend from the mountain crests to as high as 5000 feet above the tropopause. Curving jet streams are likely to have turbulent edges, especially those that curve around a deep pressure trough.

What is Clear Air Turbulence [CAT]?

Turbulence not associated with visible moisture. It is most commonly associated with jet streams [tropopause] or with mountain wave activity. It is more often encountered over land than over water.

What do you know about Jet streams?

Jet streams are narrow bands of exceedingly high-speed winds are known to exist in the higher levels of the atmosphere at altitudes ranging from 20,000 to 40,000 feet or more. The jet stream appears to be closely associated with the tropopause and with the polar front. It typically forms in the break between the polar and the tropical tropopause where the temperature gradients are intensified. The mean position of the jet stream, shears south in winter and north in summer, with the seasonal migration of the polar front. Because the troposphere is deeper in summer than in winter, the tropopause and the jets will nominally be at higher altitudes in the summer. Long, strong jet streams are usually also associated with well-developed surface lows beneath deep upper troughs and lows. A low developing in the wave along the frontal surface lies south of the jet. As it deepens, the low moves near the jet. As it occludes, the low moves north of the jet, which crosses the frontal system, near the point of occlusion. The jet flows roughly parallel to the front. The subtropical jet stream is not associated with fronts but forms because of strong solar heating in the equatorial regions. The ascending air turns pole ward at very high levels but is deflected by the Coriolis force into a strong westerly jet. The subtropical jet predominates in winter.

The jet streams flow from west to east and may encircle the entire hemisphere. More often, because they are stronger in some places than in others, they break up into segments some 1000 to 3000 nautical miles long. They are usually about 300 nautical miles wide and may be 3000 to 7000 feet thick. These jet stream segments move in an easterly direction following the movement of pressure ridges and troughs in the upper atmosphere.

Winds in the central core of the jet stream are the strongest and may reach speeds as great as 250 knots, although they are generally between 100 and 150 knots. Wind speeds decrease toward the outer edges of the jet stream and may be blowing at only 25 knots there. The rate of decrease of wind speed is considerably greater on the northern edge than on the southern edge. Wind speeds in the jet stream are, on average, considerably stronger in winter than in summer.

Which way does the earth turn about its axis? [Draw on whiteboard]

Draw a picture of the earth on a white board.

What does windshear do, what is your procedure if you

….Hmmm….

There is a thunderstorm on final, what do you think about?

Possible windshear and turbulence
Possible reduction in visibility
Possibility of lightning strike
Consider holding until the storm passes

What are the standard, the dry and the saturated adiabatic lapse rates?

Environmental Lapse Rate [ELR]: 1.98º C / 1000’
Dry Adiabatic Lapse Rate [DALR]: 3.0º C / 1000’
Saturated Adiabatic Lapse Rate [SALR]: 1.7º C / 1000’

SALR varies depending on the original temperature of the rising air, and averages about 1.7º C / 1000’.

Unstable air occurs when the actual lapse rate is greater than the DALR, conditionally unstable air, when the actual lapse rate is between the DALR and the SALR, and stable air, when the actual lapse rate is less than the SALR.

Saturation: The state where the air reaches 100% humidity.

What is the Inter-Tropical Convergence Zone?

On or near the equator, where average solar radiation is greatest, air is warmed at the surface and rises. This creates a band of low air pressure, centred on the equator. This rising air comprises one segment of a circulation pattern called the Hadley Cell. The rising air is replaced by the Trade winds approaching the equator from north and south. As the trade winds meet near the equator, surface convergence and uplift take place. For this reason the equatorial band of low pressure is called the Equatorial Trough, Intertropical Convergence Zone, or the ITCZ. The ITCZ is a region of light winds, which lends it the name the doldrums. The convergence of the Southeast and Northeast Trade Winds, within the doldrums, creates a zone of Cumulus clouds and attendant shower activity. Cumulus clouds often build up to great heights. Aircraft reports have estimated tops of Cumulonimbus to be as high as 12,000m. The ITCZ varies from 20 miles to as much as 300 miles in width, and typically has an undulating conformation.

We are interested in the ITCZ because, under certain circumstances, tropical depressions on the ITCZ intensify to hurricanes. It may seem puzzling that the ITCZ can produce cyclones, when the Coriolis force is at its weakest near the equator. The answer to this puzzle lies in the fact that the ITCZ is not stationary on the equator, but migrates north and south with the seasons. The ITCZ moves north during the high-sun season of the Northern Hemisphere, and south during the high-sun season in the Southern Hemisphere. These movements are not perfectly symmetrical above and below the equator, because of the influence of landmasses, among other factors. When the ITCZ is near the equator, the convergence of surface winds along the ITCZ is likely to take the form of parallel flow, with easterly wind approaching the doldrums from both north and south. When the Trade Winds converging at the ITCZ are weak and nearly parallel to it, the ITCZ tends to narrow in width, and show little shower activity. When the ITCZ lies south of the Geographic Equator, as it does in the Western Pacific and Indian Oceans, the Northeast Trade Winds acquire a northwesterly direction after crossing the equator (because the Coriolis force changes direction below the equator!) In this situation the convergence is strong and favours the formation of a Tropical Depression When the ITCZ lies north of the Geographic Equator, the Southeast Trade Winds acquire a southwesterly direction after crossing the equator and again the convergence pattern favours the formation of a Tropical Depression. Tropical depressions tend to move from east to west at a rate of about 10 to12 knots. In most cases these disturbances are short-lived. Surface winds attending a tropical depression usually do not exceed 25 knots. The enclosing isobar has an elongated oval shape, the width of the ITCZ is greater in the region enclosed by the isobar[s], and the ITCZ exhibits a deflection away from the Geographic Equator.

There is a definite connection between the seasonal position of the Equatorial Trough and zones of hurricane formation, which is borne out by the fact that no hurricanes occur in the South Atlantic [where the trough never lies south of 5 deg S [or in the southeast Pacific [where the trough remains north of the equator]. On the other hand, satellite photographs over the northeast Pacific show an unexpected number of cyclonic vortices in summer, many of which move westwards near the trough line about 10 deg -1 deg N.

Tell me about the Monsoon.

Monsoons are cyclical wave-like air masses that occur in the sub-tropics, moving onto land from the sea during the summer and returning over water in winter. The word monsoon comes from the Arabic mausim, meaning, ‘season,’ because these storms return year after year. The term monsoon refers to large-scale seasonal reversals of the wind regime. Such seasonal wind shifts at the surface are quite widespread and occur in many regions. The Asiatic seasonal wind reversal is notable for it’s immense extent and the penetration of its influence beyond tropical latitudes. Monsoons develop as a result of changing patterns of atmospheric pressure caused by the varied heating and cooling rates of continental landmasses and oceans. The strongest and most well known monsoons are those, which affect India and Southeast Asia. The summer monsoon, which blows south-westerly across the Indian Ocean, is extremely wet. The winter monsoon, in contrast, blows northeasterly and is generally dry.

India and Southeast Asia lie in between the centres of the tropical and subtropical climate zones. For much of the year, and particularly during winter, northeast trade winds blow across the region, from subtropical high pressure to equatorial low pressure. These winds originate from the continental interiors and are generally dry. During the summer months however, the large landmasses of Asia and the Indian subcontinent heat up, generating a seasonal continental region of low pressure. Airflow reverses and wind blows southwesterly across the Indian Ocean, accumulating considerable moisture, which is deposited as heavy rainfall during the wet season from May to September. Scientists have linked the development of the monsoonal wind phenomenon over India during Earth History to the uplift of the Himalayas and the Tibetan Plateau, which occurred about 20 million years ago, when India collided into the Asian continent. The cycle continues as the cooling air creates precipitation and releases more energy. This energy then heats the air, which rises and flows back to the sea, cools, descends, and rushes back to land to replace more warm, rising air. This monsoon is centred over continental Asia.

Tell me about a cold front.

The cold front represents the leading edge of a cold air mass. The frontal zone has a steeper slope [2Ëš] and means the poor weather associated with a cold front is of shorter duration than a warm front. There may be frontal thunderstorm activity and associated precipitation. At the passage of a cold front the wind veers sharply, pressure begins to rise and temperature falls.

Tell me about a warm front.

The warm front represents the leading edge of a warm air mass. The frontal zone has a very gentle slope [0.5-1˚], so cloud systems associated with a warm front [cirrus, cirrostratus and altostratus] indicate its approach 12 hours or more before it’s arrival. At the passage of a warm front, the wind veers, temperature rises and the fall of pressure is checked. The rain then becomes intermittent or ceases in the warm air and the thin stratocumulus cloud sheet may break up.

Can a typhoon/cyclone cross the equator?

Yes. Once established, it can cross about 5Ëš latitude into the opposite hemisphere. In so doing it will encounter opposing Coriolis force and rapidly decrease in strength.

Which direction do they travel?

Northern hemisphere: North/northwest
Southern hemisphere: South/southwest

Which way do they turn?

Depends on the hemisphere

Where do Typhoons form?

Formation usually occurs between 5Ëš and 15Ëš north/south latitude, over a warm ocean.

What do you know about tropical cyclones/hurricanes (typhoons)?

Most typhoon activity occurs during late summer and autumn [both hemispheres], during times of maximum northward and southward displacement of the equatorial trough. Begins life as a tropical depression and develops with favourable conditions into a tropical storm. Main energy source is latent heat from condensed water vapour. A cold-cored tropical storm is transformed into a warm-cored hurricane in association with the release of latent heat in CB towers [approximately 100-200 CB towers]. The warm core is vital to hurricane growth as it intensifies the upper anticyclone, leading to a feedback effect by stimulating the low level influx of heat and moisture, which further intensifies convective activity, latent heat release and therefore upper level high pressure. Formation of an eye is an essential part of the life cycle of a hurricane. The diameter of the eye is around 30-50km and within it, the wind is virtually calm and the cloud cover may be broken. Once developed a hurricane will usually move at 16-24km/hr in a north to north-westerly direction and a cyclone will move in a south to south-westerly direction.

Conditions for formation:

  • Ocean surface temperature of 26.5Ëšc or greater (enhances evaporation)
  • Ocean depth of 50m or more [unknown why]
  • A Low-pressure system [initial disturbance]
  • Sufficient Coriolis force [between 5Ëš and 15Ëš n/s]
  • Low values [less than about 20 kts] of vertical wind shear, between the surface and the upper troposphere.

A supply of heat and moisture combined with low frictional drag at the sea surface, the release of latent heat through condensation and removal of air aloft are essential conditions for the maintenance of a typhoon.

Tropical Classification
Tropical Disturbance: [weak area of low pressure]
Tropical Depression: [20-34 kts and a “closed” Circulation] [Storm number]
Tropical Storm [35-64 kts] [storm name]
Hurricane [65+ kts or 74+ mph]

Saffir-Simpson Scale

Maximum Winds and Central Pressure

Category 1 65- 82 kts; > 979 Hpa
Category 2 83- 95 kts; 965-979 Hpa
Category 3 96-113 kts; 945-964 Hpa
Category 4 114-135 kts; 920-944 Hpa
Category 5 > 135 kts; < 920 Hpa

Tropical Disturbance
A discrete tropical weather system of apparently organized convection – generally 200 to 600 km [100 to 300 nm] in diameter – originating in the tropics or subtropics, having a no-frontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field. Disturbances associated with perturbations in the wind field and progressing through the tropics from east to west are also known as easterly waves.

Tropical Depression
A tropical cyclone in which the maximum sustained wind speed [using the U.S. 1 minute average standard] is 33 kts or less. Depressions have a closed circulation.

Tropical Storm
A tropical cyclone in which the maximum sustained surface wind speed [using the U.S. 1 minute average standard] ranges from 34 kts to 63 kts. The convection in tropical storms is usually more concentrated near the centre with outer rainfall organizing into distinct bands.

Typhoon
When winds in a tropical storm, equal or exceed 64 kts it is called a Typhoon. Typhoons designated categories 3, 4 or 5 on the Saffir-Simpson scale are known as major or intense.

What is the value of the Coriolis parameter, at the equator?

Zero

What is Coriolis parameter?

The Coriolis force is a deflecting force, which is maximum at the poles and reduces to zero at the equator. The Coriolis force always acts at right angles to the direction of the air motion to the right in the northern hemisphere and to the left in the southern hemisphere. The formula for Æ’ [Coriolis parameter] is

-2ωV sin Φ

ω = angular velocity [earths rotational velocity 15º/hr]

V = velocity of the mass

Φ = latitude [sin 0º = 0,sin 90º = 1]

What is the ICAO standard atmosphere?

+15ºc
1013.2 Hpa
2ºc /1000’ lapse rate until 36 000’ [tropopause] Isothermic at -57ºc
1 Hpa = 30’

Volcanic ash encounters. What do you know about it?

Volcanic ash encounters
Despite ongoing avoidance efforts, operators can still experience volcanic ash encounters. Guidance on the operational issues surrounding volcanic ash is divided into three aspects: avoidance, recognition, and procedures. The following information is general; flight crews should refer to their respective company’s operating manuals for details.

Avoidance
Preventing flight into potential ash environments requires planning in these areas: Dispatch needs to provide flight crews with information about volcanic events, such as potentially eruptive volcanoes and known ash sightings, that could affect a particular route.
Dispatch also needs to identify alternate routes to help flight crews avoid airspace containing volcanic ash. Flight crews should stay upwind of volcanic ash and dust. Flight crews should note that airborne weather radar is ineffective for distinguishing ash and small dust particles.

Recognition
Indicators that an airplane is penetrating volcanic ash are related to odour, haze, changing engine conditions, airspeed, pressurization, and static discharges.

Odour
When encountering a volcanic ash cloud, flight crews usually notice a smoky or acrid odour that can smell like electrical smoke, burned dust, or sulphur.

Haze
Most flight crews, as well as cabin crew or passengers, see a haze develop within the airplane. Dust can settle on surfaces.

Changing engine conditions
Surging, torching from the tailpipe, and flameouts can occur. Engine temperatures can change unexpectedly, and a white glow can appear at the engine inlet.

Airspeed
If volcanic ash fouls the Pitot tube, the indicated airspeed can decrease or fluctuate erratically.

Pressurization
Cabin pressure can change, including possible loss of cabin pressurization.

Static discharges
A phenomenon similar to St. Elmo’s fire or glow can occur. In these instances, blue-coloured sparks can appear to flow up the outside of the windshield or a white glow can appear at the leading edges of the wings or at the front of the engine inlets.

Procedures 
The following nine procedures are general recommendations. Each operator’s flight operations manuals will include more specific directions.

Reduce thrust to idle immediately
By reducing thrust, engines may suffer less build-up of molten debris on turbine blades and hot-section components. Idle thrust allows engines to continue producing electrical power, bleed air for pressurization, and hydraulic power for airplane control.

Turn the auto throttles off
This prevents the engines from increasing thrust above idle. Ash debris in the engine can result in reduced surge margins, and limiting the number of thrust adjustments improves the chances of engine recovery.

Exit the ash cloud as quickly as possible
A 180-deg turn out of the ash cloud using a descending turn is the quickest exit strategy. Many ash clouds extend for hundreds of miles, so assuming that the encounter will end shortly can be false. Climbing out of the ash could result in increased engine debris build-up as the result of increased temperatures. The increased engine build-up can cause total thrust loss.

Turn on engine and wing anti-ice devices and all air-conditioning packs
These actions improve the engine stall margins by increasing the flow of bleed air.

If possible, start the auxiliary power unit [APU]
The APU can power systems in the event of a multiple-engine power loss. It can also be used to restart engines through the use of APU bleed air.

If volcanic dust fills the flight deck, the crew may need to use oxygen Use flight deck oxygen at the 100 percent setting.
Manual deployment of the passenger oxygen system is not required because it will deploy automatically if the cabin altitude exceeds 14,000 ft.

Turn on the continuous ignition
Confirm that auto start is on, if available. In the event that the engines flame out or stall, use appropriate procedures to restart the engines. During restart, the engines may take longer than normal to reach idle thrust due to the combined effects of high altitude and volcanic ash ingestion. If an engine fails to start, try restarting it again immediately. Flight crews should remember that the airplane may be out of the air start envelope if the encounter occurs during cruise.

Monitor engine exhaust gas temperature (EGT)
Because of potential engine debris build-up, the EGT can climb excessively. The flight crew should prevent EGT accedences. Shut down the engine and restart it if the EGT is approaching limits similar to a hung start.

Fly the airplane by monitoring airspeed and pitch attitude
If necessary, follow the procedure for flight with unreliable airspeed.

What is the biggest hazard in heavy rain on final approach?

  • Reduced visibility
  • Possible windshear
What causes saturation?

Cooling temp to dew point
Evaporations brings dew point to temp [adds moisture to air]

Here are some visibility definitions…

Visibility: the ability to see prominent unlighted objects by day and prominent lighted objects by night, expressed in nm.

Flight visibility: average forward horizontal distance measured in nm from the cockpit in flight

Prevailing visibility: greatest forward horizontal visibility, SM, equal or exceeded throughout at least half of the horizon circle, which need not be continuous

Runway Visual Range: horizontal distance a pilot will see by looking down the runway from the approach end

Slant Range visibility: distance on final approach when you can see the runway

Obscuring Phenomena: any collection of particles, which will reduce horizontal visibility

Ceiling: height AGL to the lowest broken or overcast layer, or the vertical visibility into obscuring phenomena

Vertical visibility: distance seen directly upward from the ground level into obscuring phenomena

What causes greatest change in Altimeter, Air Speed, and Rate of Climb?

Icing is greater than pressure.
Affects are due to Pitot-Static clogs.

What kind of ice does freezing rain cause?

Clear ice.

At what temp does structural icing occur?

Below 0ºC.

What weather conditions form frost?

Little or no wind
Lack of clouds
OAT below freezing
Dew point within 5ºC of air temp

Define wind shear…

Sudden change in wind direction and or speed over a short distance.

What is mechanical turbulence?

Any irregular terrain. Mountains, buildings, trees…

What is convective instability?

Dry air over moist air
Moist air over dry air

What weather conditions form tornadoes?

Marked convective instability
Pronounced horizontal wind shear
Rapid moving cold fronts or squall lines
Strong convergence

What is the order of precedence when flying around thunderstorm

Go around
Fly over the top
Fly below
Fly through the lower 1/3

What does it require for a thunderstorm to develop?

Lifting [most likely convergence]
Unstable air
Moisture content in the air
Building clouds through the freezing level

What are the worst hazards of squall lines or thunderstorms?

Primary: turbulence
Secondary: hail

What are the general conditions of occlusions?

A combination of warm and cold fronts.

Describe the two types of occlusions…

Occlusions have three air masses and two fronts.
Left side is behind, right side is ahead.

Describe the three parts of air mass classification…

First is source region. [Arctic, Polar, Tropical, Equatorial]
Second is surface of their source region. [Maritime or Continental]
Third is temp [cold or warm]

What is the temp. relationship between air and land?

Air temp is relative to surface below it.
Summer time, air masses are cold,
Winter air masses are warm.

Define air mass…

A large body of air that has essentially uniform temperature and moisture conditions, in a horizontal plan.

What are the three types of stability?

Stable: Air is pushed up until lifting action is removed, air is colder than the surrounding air, so it falls to its original position

Unstable: Air is pushed up until lifting action is removed, air is warmer than the surrounding air, so it is pushed up and continues to rise

Neutral: Air is pushed up until lifting action is removed, air is the same temp as the surrounding air and therefore it remains in place

Flight Conditions                Stable Atmosphere                     Unstable Atmosphere
Cloud type                          Stratus                                          Cumulus
Turbulence                          Smooth                                         Rough
Visibility                               Poor                                             Good (outside cloud)
Winds                                  Steady                                         Gusty
Precipitation                        Steady                                          Showery
Icing                                    Rime                                             Clear
Air Mass                              Warm                                            Cold
Front                                   Warm                                            Cold

What are the 4 lifting actions and their differences?

  • Convergence: winds meet, cause air to move vertically
  • Orographic: wind runs into terrain, so it is lifted
  • Frontal: front moves in, air is pushed up
  • Thermal: sun heats land, land gives off heat, warm air rises
The two types of weather conditions that cause icing are…

  • Supercooled water [freezing rain]
  • Wet snow
What is the difference between relative humidity and specific humidity?

Relative Humidity measures the percent of saturated air or what percentage of the bucket is filled with water.

Specific humidity measures how much water vapour is contained per unit mass of air or how much water is in the bucket.

Humidity definitions…

Relative Humidity: percentage of saturated air

Specific Humidity: Ratio of water vapour per unit mass of air. The higher the dew point the higher the specific humidity.

What two forces cause winds to travel parallel to isobars?

Coriolis Force: bends gradient winds to the right, do not affect surface wind because of friction.

Pressure Gradient Force: initiating force for all winds.

What kinds of drifts are associated with a high-pressure area?

High-pressure area, winds flow clockwise.
Fly into a high, you get right cross wind and left drift

What 3 elements are associated with moisture?

Clouds
Humidity
Precipitation

Define the tropopause…

Transition zone between the troposphere and the stratosphere Temperature is isothermal with altitude An abrupt change in rate of temperature decrease with increasing altitude marks this boundary It’s a region not a layer

Where can Rime Ice occur?

Rime ice can be expected in stratiform clouds since vertical currents are not strong enough to support large droplets.

What is Rime Ice?

Rime ice is a milky white, opaque, and granular deposit of ice formed through the rapid freezing of small super-cooled water droplets. Rime ice is most likely to occur at temperatures of –10 to –20.

Where does clear ice occur?

Clear ice occurs in cumuliform clouds with appropriate temperatures where vertical currents can support large drops.

When will clear ice normally occur at?

Clear ice normally occurs at temperatures between 0C and –10C in, but may occur with temperatures as cold as –25. Clear icing is the most severe form of icing.

What happens to ice formation with an increase in airspeed?

As airspeed is increased more water is encountered over a given period of time and therefore the rate of deposit is increased.

What factors affect the rate of ice accumulation on an aircraft?

The following items affect the rate of ice accumulation on an aircraft:

The size and number of water drops in a given volume of air, airfoil thickness, and airspeed.

Since thick airfoils have a larger deflective force they collect ice more slowly than thin airfoils, which have a smaller deflective force. Droplet size also is a factor. Smaller drops have a greater tendency to follow the air stream and larger droplets resist this deflecting force.

When may freezing rain be encountered?

Freezing rain or drizzle may be encountered in the clear air below a cloud layer.

When may structural ice form?

Structural Ice may form when the free-air temperature is 0C or colder.

What are the three requirements for the formation of icing?

There three requirements for the formation of structural icing are as follows: Outside air temperature below freezing, aircraft skin temperature below freezing, and visible moisture.

How does Wet Snow Form?

Wet Snow occurs at temperatures just below freezing and can come about as the result of turbulence in the air and the resulting mixture of super cooled moisture.

What is super cooled water?

Super Cooled water is liquid water found at air temperatures below freezing. Super cooled water droplets are numerous in clouds at temperatures between 0C and –15C with decreasing amounts at colder temperatures.

What are the cumulative effects of icing?

Lift decreases, weight increases, Drag increases, Thrust Decreases, Fuel consumption increases, and stall speed increases.

How do you fly the aircraft in turbulent weather?

One rule for Turbulent Flight: Trim the aircraft for level flight at the recommended turbulent air penetration airspeed. Severe turbulence may cause large and rapid variations in indicated airspeed. Don’t chase airspeed.

Discuss Wind Shear Turbulence.

Wind Shear Turbulence is defined as a sudden change in wind direction and or speed over a short distance. The greater the change in wind speed and/or direction in a given direction, the more severe the turbulence. These turbulent wind shear flight conditions are frequently encountered in the vicinity of the jet stream where large shears in both the horizontal and vertical planes are found as well as I association with land and sea breezes, fronts, inversions, and thunderstorms.

What are the rules that should be applied when mountain wave turbulence has been forecasted?

Avoid the turbulence if possible by flying around the areas where wave conditions exist. If this is not feasible, fly at a level that is at least 50% higher than the height of the highest mountain range along your flight path. This procedure will now keep the aircraft out of turbulence, but provides a margin of safety if a strong downdraft is encountered.

Avoid the rotor, lenticular, and cap clouds since they contain intense turbulence and strong updrafts and down drafts.

Approach the mountain range at a 45-degree angle, so that a quick turn can be made away from the ridge if a severe downdraft is encountered.

Do not place too much confidence in your pressure altimeter reading near mountain peaks. They may indicate altitudes, which are more than 2500 feet higher than your true altitude.

Penetrate turbulent areas at air speeds recommended for your aircraft.

Where is the extreme turbulence found when near mountains?

Severe turbulence can be frequently found from the surface to the tropopause and 150 miles downwind when the winds are greater than 50 knots at the mountaintop. Extreme turbulence is usually found at low levels on the leeward side of the mountain in or near the rotor and cap clouds when the winds are 50 knots or greater at the mountaintop. Moderate turbulence often can be experienced out to 300 miles under the previously stated conditions.

What are rotor clouds, cap clods, and Lenticular Clouds?

The rotor clouds forms at a lower level and is generally found at about the same height as the mountain ridge. The cap cloud usually obscures both sides of the mountain peak. The lenticular clouds like the rotor and cap clouds are stationary in position.

What does the strength and magnitude of Mechanical Turbulence Depend on?

The strength and magnitude of mechanical turbulence depends on the speed of the wind, the roughness of the terrain, and the stability of the air.

How does Mechanical turbulence Work?

When the air near the surface of the earth flows over obstructions, such as irregular terrain, or buildings, the normal horizontal wind flow is disturbed and transformed into a complicated pattern of eddies and other irregular air movements.

What is the worst thermal?

A ploughed field.

How does Thermal Turbulence Work?

Vertical air movements resulting from convective currents develop in air, which is heated by contact with a warm surface. This heating from below occurs when either cold air is moved over a warmer surface, or the ground is strongly heated by solar radiation.

How can Turbulence be divided up?

Types of Turbulence can be divided according to causative factors: Thermal, mechanical, frontal, large-scale wind shear.

What are the reporting term definitions?

Occasional: Less then 1/3 of the time. I
ntermittent: 1/3 to 2/3rds of the time.
Continuous: More than 2/3rds of the time.

What are the four intensities of turbulence?

Light, Moderate, Severe, Extreme

Discuss actions within a storm.

Once inside the storm, the pilot should let the plane ride out the updrafts and downdrafts and concentrate on maintaining a level attitude. With power set to maintain the proper airspeed, maintaining the same attitude will result in only minor airspeed variations. However, the aircraft’s altitude may vary by thousands of feet. The rapidly changing pressure conditions within the storm will result in unreliable indications and erratic variations in altitude, airspeed, and rate of climb instruments. Since the attitude gyro is independent of the Pitot-static system, its indications should be considered reliable.

How should Thunderstorms be avoided?

Fly around them
Fly over the top of the storm
Fly below the storm
If not possible to avoid the storm, fly through the lower 1/3 of the storm

What are some good cues about microbursts coming from departure and arrival reports?

Departure or arrival weather reports calling for gusty winds, heavy rain, or thunderstorms should be a clue that a high potential for microburst activity exists.

What are the best sources of information?

PIREPS [Pilot Reports] and Weather Alerts are one of the best sources of information.

How does a LLWAS work?

For example, the Low Level Winds Shear Alert System [LLWAS] Measures the winds speed and direction at several points on the ground and compares them with a reference sensor located near the centre of the airfield.

What are the four methods of detection, and the three wind shear alert systems used?

4 methods of detection:
Visual
PIREPS, and weather reports
Wind shear alert systems
Doppler radar, and LLWAS

What are the visual cues for a microburst?

Visual clues include virga, localized blowing dust, rain shafts with rain diverging away from the core of the cell, roll clouds, and of course and indication of vivid lightning or tornado-like activity.

How long does a microburst last?

A microburst normally lasts from five to ten minutes after its diverging wind flow first hits the earth’s surface.

What are the hazards associated with Thunderstorms?

Thunderstorms are accompanies by some or all of the following hazards: extreme turbulence, hail, microburst, icing, lighting, and tornadoes. Turbulence and hail are the greatest hazards and are found in the upper 2/3rds of a mature stage cell.

What happens to pressure when a storm approaches?

Large pressure changes can accompany thunderstorm formation.

What are the basic requirements for a formation of a thunderstorm?

The basic requirements for the formation of a thunderstorm [Cumulonimbus cloud] are as follows: lifting action, unstable air, high moisture content, and a cloud building through the freezing level.

What sort of weather is associated with occluded fronts?

Since the occluded front is the result of meeting of a cold front and a warm front, the weather associated with the occlusion will be a combination of both types of frontal weather. If an occlusion is approaching from the east, you would first encounter warm front type weather which may extend for several hundred miles to the east of the surface front. On the other hand, if it were approached from the wet you would first encounter cold front type weather.

What does the widespread precipitation area ahead of a warm front often result in?

The widespread precipitation area ahead of a typical warm front often results in low stratus and the formation of fog. The widespread precipitation area ahead of a typical warm front often results in low stratus and the formation of fog.

What is some extreme weather conditions associated with squall lines?

Squall lines contain severe weather conditions including the following: extreme turbulence, heavy rain, lightning, icing, and frequently hail, and/or tornadoes.

What does the extent of cloudiness in cold air depend on?

The extent of the cloudiness in the cold air depends on the degree of stability and moisture content of the cold air mass.

Discuss pressures with relation to fronts.

All fronts are located in troughs of low pressure and the lowest pressure will extend from the low centre along this trough. Therefore, when a front approaches a station, or a pilot flies toward a front, the pressure decreases. Pressure normally rises immediately following frontal passage. Because of this pressure change, it is extremely important to obtain a new altimeter setting the vicinity of a front.

How do you locate and classify fronts?

Differences in the various properties of adjacent air masses, such as temperature, moisture, wind, and pressure are used to locate and classify fronts.

Describe Maritime Tropical Cold Air as they move over the ground.

By the afternoon, these often build into towering cumulus and cumulonimbus clouds resulting in scattered rain showers and thunderstorms.

What happens with air with high moisture content?

Due to the high moisture content of the air (Tropical Warm), condensation may result in fog, low stratus, steady precipitation, or any combination of these.

Describe air masses flowing over ground, with heating and cooling.

If the air mass is warmer than the surface, it is cooled by contact with the cold ground, becomes more stable, and is called a warm air mass. If the air mass is colder than the surface over which it is moving, it is heated from below, resulting in convective currents and instability, and is called a cold air mass.

Describe Maritime and Continental fronts.

Maritime has high moisture content, Continental has Low.

What is an adiabatic process?

An adiabatic process occurs when the temperature of a body of air changes without heat being added or taken away. When a parcel of air is lifted in the atmosphere, it expands due to decreasing pressure.

Describe Lifted Air….

Lifted air that is colder than the surrounding air settles when the lifting action is removed since it is denser. This indicates a stable condition. Lifted air that is warmer than the surround air continues to rise when the lifting action is removed because it is less dense indicates an unstable condition.

What is a nimbostratus cloud?

Dark massive cloud layers having a wet appearance and accompanied by heavy steady precipitation such as rain or snow. This cloud is classified as a middle cloud.

What can you tell us about stratus clouds

Form in layers with smooth bases and tops. They are grey in appearance when viewed from the surface, and often cover the entire sky. The stable air that gives stratus clouds their layered characteristics also inhibits the vertical spread of smoke, dust and haze particles and thus tends to lower visibility. Precipitation, when occurring, is generally light steady rain or drizzle. Stratus clouds are generally associated with smooth flight conditions.

What can you tell us about CB’s?

Large, dense towering clouds with cauliflower-like tops. The top portion of the cloud is often flattened into an anvil shape or consists of cirrus formation resulting from ice crystals. Water droplets form the major portion of the cloud, but ice crystals appear in the upper portions. Cumulonimbus and thunderstorm are synonymous terms; they result in strong winds, lightning, and intermittent heavy showery precipitation. The well-developed cumulonimbus may be the parent of the hailstorm.

What are the types of precipitation?

Drizzle, freezing drizzle, rain, freezing rain, hail, ice pellets, snow grains, snow.

What is Dew Point Depression?

Dew Point depression is the difference, in degrees, between the air temperature and the dew point temperature. [When air temp equals dew point temp, saturation occurs].

What is Dew Point Temperature?

The temperature at which saturation occurs. It is also the temperature where moisture first starts to condense on exposed surfaces forming dew. Dew point is an indication of, and is directly related to, specific humidity.

What is Specific Humidity?

Specific humidity is the ratio of water vapour per unit mass of air, and is expressed as grams of water per kilogram of air. For a particular temperature, there is a maximum specific humidity, or maximum amount of water vapour that the air can hold. The higher the temperature, the more water vapour the air can hold.

Explain Land Breeze.

At night, the circulation is reversed so that the air movement is from land to sea, producing an offshore wind called the land breeze.

Explain Sea Breeze.

During the day, the pressure over the warm land becomes lower than that over the colder water. The cool air over the water moves toward the lower pressure, forcing the warm air over land upward. The resulting onshore wind is called a sea breeze. Sea breezes of 15 to 20 knots are not uncommon.

How does something get classified as a Jet Stream?

To be classified as a jet, it is generally accepted that the winds must be 50 knots or greater and the core, area of maximum wind, must possess considerable length.

What is Buys Ballot’s Law?

This law states that if the wind is at your back, the area of lower pressure will be to your left.

Given a gradient wind, calculate a surface wind.

Subtract 45 degrees.

What does surface friction do to the wind speed?

How does this affect the Coriolis force? Surface friction reduces the speed of the wind. Since magnitude of Coriolis force varies with the speed of wind, a reduction in the wind speed by friction causes a reduction in the Coriolis force.

What direction and altitude do gradient winds flow?

Gradient winds flow parallel to the isobars and above 2000 AGL. Note: PGF and Coriolis force cause gradient winds to travel parallel to the isobars.

Define Pressure Gradient

e rate of change in pressure with horizontal distance between a high and low-pressure area is called pressure gradient. Large differences in pressure between horizontal points result in stronger pressure gradient forces. This Pressure gradient force is the initiating force for all winds. Close spacing of isobars indicates greater pressure gradients and higher wind speeds.

What are the factors that influence actual circulation?

This circulation is modified considerably by:
The irregular distribution of oceans and continents
The relative effectiveness of differing surfaces in transferring heat to the atmosphere Irregular terrain
Daily variations in temperature
The changes of seasons
And many other factors

What is circulation, and how is it created?

Circulation is the recurring movement of air relative to the earth’s surface. It is created primarily by the large temperature difference between the tropics and the Polar Regions, and complicated by uneven heating of the land and water areas by the sun.

How does air temperature relate to indicated altimeter reading?

If the air is colder than the standard atmosphere, the aircraft will be lower than the altimeter indicates. If the air is warmer than standard, the aircraft will be higher than the altimeter indicates.

What are the pressure rules?

High to low, look out below Low to high, plenty of sky

What is Density Altitude, and how is it found?

Density altitude is the altitude in the standard atmosphere what has the same density as the local air. It is found by correcting the pressure altitude for non-standard temperature deviations.

What is pressure altitude?

Pressure altitude is the height above the standard datum plane of 1013Hpa when above 10,000 ft in Australia

What happens when in between isobars, especially when they are close together?

The rate of pressure change in a direction perpendicular to the isobars (horizontal distance) is called the pressure gradient. The gradient is steep, or strong, when the isobars are close together, and is shallow, or weak, when the isobars are far apart. Pressure gradient is the initiating force for all winds.

What is Sea Level Pressure?

Sea Level Pressure (SLP) is the pressure at mean sea level (MSL), measured directly at sea level or calculated if the station is not at sea level. Station pressure is the atmospheric pressure at an airfield or station.

What does pressure do with an increase in altitude?

Pressure, unlike temperature, always decreases with altitude.

Define an inversion.

An Inversion [inverted lapse rate] occurs when the temperature increases with an increase in altitude.

Define Lapse Rate. What is a steep, shallow, and isothermal lapse rate?

The change in atmospheric temperature with increasing altitude is called a lapse rate. The average or standard lapse rate is 2ºC per 1000′. If the temperature decreases very rapidly with altitude [greater than 3 Celsius], it is called a steep lapse rate. When the temperature decreases very gradually [Between 1.5 and 3] it is called a shallow lapse rate, while no change with altitude is called an isothermal lapse rate.

What is the horizontal transfer of heat? How is this normally accomplished?

Advection is the horizontal transfer of heat, normally by wind.

What is Convection?

Convection is the vertical transfer of heat.

What is Conduction?

Conduction is the transfer of heat from molecule to molecule by contact and it accounts for the transfer of heat between the earth’s surface and the adjacent air.

What is the process by which energy is transferred through space in the form of electromagnetic waves?

Radiation is the process by which energy is transferred through space in the form of electromagnetic waves.

Define insolation.

Insolation is the total radiation reaching the earth’s surface and it is the primary source for all weather phenomena on the earth.

What are the six primary flight hazards?

The six primary flight hazards are turbulence, thunderstorms, wind shear, icing, low ceilings, and low visibility.

What are the six weather elements?

Weather, as a broad subject, is often classified as being composed of six weather elements: Temperature, atmospheric pressure, wind, humidity, clouds, and precipitation. The last three are all associated with moisture.

What is the percentage by volume of water vapour in the atmosphere?

The atmosphere also contains water vapour amounting to 0% to 5% by volume.

What Is the Stratosphere?

The stratosphere is characterized by increasing temperature with increasing altitude.

What is the tropopause? Why is this “boundary” significant?

An abrupt change in the rate of temperature decrease with increasing altitude marks the boundary, called the tropopause.

What happens to the atmosphere with altitude? Where does most of the weight of the atmosphere reside?

The atmosphere becomes less dense with altitude, and roughly 50% of it, by weight, lies below 18,000 ft, and 90 % within 53,000 feet. Within the troposphere, the temperature normally decreases with increasing altitude.

What causes fog?

Fog forms when the relative humidity reaches 100%, and the air temperature tries to drop below the dewpoint, causing the water vapour to condense. Fog is cloud in contact with the ground. It can form in a number of ways, depending on how the cooling that caused the condensation occurred:

Radiation fog is formed by the cooling of land after sunset by thermal [infrared] radiation in calm conditions with clear sky. The cool ground then produces condensation in the nearby air by conduction. In perfect calm the fog layer can be less than a metre deep but turbulence can promote a thicker layer [wind of 2-8kts will deepen the fog]. Radiation fog is generally associated with a high-pressure system and will usually not persist long past sunrise.
Advection fog occurs when moist air passes over cool ground by advection [wind] and is cooled. This form is most common at sea when tropical air encounters cooler higher-latitude waters. It is also extremely common as a warm front passes over an area with significant snow pack.

Micro burst alerts and severe turbulence alerts. What do you know about it?

The definitions of the alerts and the order in which they are prioritised is as follows:

TDWR Microburst Alert (MBA*) [Loss of 30 knots or greater]

Terrain-Induced (TIWT*) [Windshear-loss of 30 knots or greater]

Terrain-Induced (TIWT) [Windshear-gain of 30 knots or greater]

Terrain-Induced (TIWT) [Severe Turbulence] TDWR Windshear Alert (WSA*) [loss or gain of 15 to 30 kts]

Terrain-Induced (TIWT) [Windshear-loss or gain of 15 to 30kts]

Terrain-Induced (TIWT)

Moderate Turbulence

No Alert

* MBA [Microburst Alert]
* TIWT [Terrain induced Windshear and turbulence]
* WSA [Windshear Alert]

Ever heard about a Windshear and Turbulence Warning System [WTWS]

Hong Kong’s Chek Lap Kok Airport [VHHH] is located on partly reclaimed land adjacent to Lantau Island, whose rugged terrain has a maximum elevation of nearly 3,280’. Consequently, aircraft operating at the new airport may be affected by significant terrain-induced windshear and turbulence under certain meteorological conditions.

In order to enhance safety and operational efficiency at the airport, an operational Windshear and Turbulence Warning System [WTWS] developed by a company called Weather Information Technologies Inc. [WITI] was introduced. This system provides alerts for terrain- and convective-induced windshear and turbulence and has been utilized by air traffic controllers and pilots since the airport’s opening day, 6 July 1998.

In addition to providing real-time windshear and turbulence alerts to controllers and pilots, the system provides up to 12-hour forecasts of terminal area turbulence to aviation meteorologists. The WTWS was previously known as the OWWS – the Operational Windshear Warning System. To utilize this system efficiently, it is important that pilots understand how this system was developed, what it can do and what its limitations are.

Prior to the development of the windshear warning system, several studies were conducted in Hong Kong to gain an insight into the meteorological conditions near the location of the new airport. These studies included analysis of routine weather observations, special observing programs and meteorological modelling of the differences between the old Kai Tak Airport and at Chek Lap Kok. Variables analysed included wind direction and speed, temperature, clouds, visibility, rainfall, thunderstorms and fog. Methods used to conduct these studies included investigative flights by light aircraft and water tank and wind tunnel experiments. The 44-month project was under the sponsorship of the Hong Kong Observatory. The WTWS development team included WITI, the National Centre for Atmospheric Research (NCAR), Hong Kong University of Science and Technology [HKUST], and the University of Wyoming.

Components include basic and applied research on wind flow over Hong Kong’s terrain; a scientific field study, warning system concept and feasibility studies, system design, development, testing, implementation and training. The WTWS provides real-time hazardous weather information to air traffic controllers and pilots to enhance safety in the terminal area and improve predictions of hazardous weather to support strategic decision making by air traffic managers. The WTWS is the first system worldwide to provide real-time alerts of terrain-induced turbulence and alerts for both convective and terrain-induced windshear, The WTWS also provides predictions of turbulence caused by terrain and airport surface wind as well as numerical weather prediction guidance. For detection of convective windshear, the WTWS relies partly on the output from a Raytheon developed Terminal Doppler Weather Radar [TDWR] at Tai Lam Chung, about 12 kilometres from Chek Lap Kok. The windshear warning system analyses TDWR signatures including gust front, precipitation intensity, and storm motion, providing an integrated alert system. It generates graphics and text designed for easy interpretation by pilots, controllers, traffic managers and aviation forecasters.

Terminal Doppler Weather Radar [TDWR]

The Terminal Doppler Weather Radar [TDWR] is proven technology and uses Doppler shift to detect convective windshear. It is already in operational use at Denver, USA, and other airports, but this will be the first time it is being used in a coastal environment with busy marine traffic.

The design criterion is for a probability of detection [POD] of 90% and a false alarm rate [FAR] of 10%. [In the USA, PODs of 95% and FARs of 3% have been achieved]. The output products are shown on a geographical situation display [GSD] and on the alphanumeric alert displays [AAD] at the air traffic controllers’ stations.

The primary WTWS product suite includes detection of terrain-induced turbulence, terrain-induced windshear, convective microburst and windshear, gust fronts, precipitation intensity and storm motion. It also predicts terrain-induced turbulence and airport surface wind and numerical weather prediction guidance. Pilots, controllers, air traffic managers and aviation forecasters easily interpret the graphical and text formats. The alerts use commonly accepted aeronautical navigation terminology. The WTWS graphic display delivers hazardous weather warning information and other meteorological products. It shows the horizontal profile of various hazardous weather areas, vertical wind profiles near the approach and departure corridors, and textual warning messages. Video replay of the recent product history is possible. The meteorological situation is displayed in several user-selectable ranges and levels of detail. Critical products and important situation changes are highlighted visually on the display and/or announced by audible signals.

User needs were established over a two-year period culminating in a prototype demonstration in October 1995. As a result of comments by users, the system was designed to provide high performance, distinguish between the phenomena of windshear and turbulence, use existing aeronautical terminology and provide spatial extent of the phenomena as well as up to 12-hour forecasts of surface wind and turbulence at a 30-minute resolution.

Alerts had to be reserved for significant events and assigned a priority. They also had to be concise but informative and provided within three nautical miles of runways. Products had to support both tactical and strategic decision-making and be updated fast enough to cover operations that occur every two minutes. The alphanumeric alarm display is designed to alert controllers to time-critical weather hazards and to provide textual warnings for communication to pilots. Alerts are given as microburst, windshear or turbulence, with associated intensity and location. For windshear and microburst alerts, intensity is given as headwind “loss” or “gain” in knots; for turbulence, intensity is specified as “moderate” or “severe”. The intensity is the maximum expected along the alert corridor and the alert location is where the event is first expected to be encountered.

Event locations for windshear alerts are given as one, two or three nautical miles on approach or departure – or on the runway. Event locations for turbulence alerts are identified as departure or approach. It was originally planned that the easterly runways [07R/L] would be the preferred runways, but it has now been suggested that it may be better to use the westerly runways whenever possible. The main reason for this change is to minimise traffic confliction with the Macau and Shenzhen airports and to overcome the problems of vectoring aircraft within Hong Kong airspace. It is too early to assess whether this may also alleviate the effects of the terrain-induced turbulence, but this is being studied at this time. It should be noted that the prevailing wind in Hong Kong is easterly.

In the summer, strong southerly winds, sometimes associated with typhoons, are present on occasions, but otherwise light winds flow from that direction. In autumn and winter, the north-easterly monsoon affects the area. It follows that during normal conditions, when operating from runways 25L/R, there will be a slight tailwind and a crosswind. The runways are approximately 3800m long and there are lesser obstacle problems to the west, so the tailwind should not be a critical factor. [The rapid exits have also been located to cater for the various different landing weights, including those specifically for fully laden cargo aircraft.]

Aircraft are positioned at approximately 15nm for 25R, which is the preferential landing runway. Pilots are able to listen to alerts being given to proceeding aircraft, which help to build up a picture of the conditions on short finals. The situation on 07R/L is not so straightforward because of the proximity of Macau and the airspace boundary. This means that aircraft are not transferred to tower control until about 7nm and so pilots will only normally hear their own specific warning.

If encountering windshear, what is the recovery technique?

Disconnect the autopilot
Aggressively apply max power/thrust
Roll wings level, unless terrain is a factor, to maximize aircraft performance
Pitch up, rotating at a normal takeoff rotation rate [2-3°/sec] to max body angle [15-17º] or until stick-shaker
Verify speed brakes are retracted
Do not alter gear/flap configuration until terrain clearance is assured [adverse effects to stall] Issue Pilot report [PIREP]

Explain windshear in a microburst.

↑ Airspeed
↓ Airspeed [rapid]
↑ Rate of descent

What do you know about windshear?

Windshear may be caused by a number of meteorological phenomenon including temperature inversions, sea breezes, frontal systems, strong surface winds and thunderstorms. Windshear is any rapid change in wind direction or velocity. Severe windshear is a rapid change in wind direction or velocity causing airspeed changes greater than 15 knots or vertical speed changes greater than 500 feet per minute.

Light: Minor excursions from flight path or speed
Moderate: Significant effect on control of the aircraft
Strong: Difficulty in keeping aircraft on desired flight path and or speed
Severe: Hazardous effects to aircraft controllability

What causes a microburst?

A microburst will usually be associated with strong updrafts. If there is virga associated with a CB, it occurs due to the preceding convective action raising the air to the saturation level, that is, the parcel of air cooled as it ascended, could no longer hold the moisture in it, it then condensed to form cloud, then coalesced to form precipitation, and started to descend in the from of rain. If there is a wind aloft, the descending air will be adjacent to the rising air. When the air below the rain is dry, the water evaporates, and forms virga. When evaporation takes place, cooling takes place through the release of latent heat. Resulting in a parcel of cool air, which already descending, begins to descend even faster.

A microburst may be dry – or wet. Those below virga are considered dry, and those in a rain shaft are considered wet microbursts. Depending on the winds aloft, a dry microburst could be in the clouds just above you and to the side of your flight path, especially if you are flying adjacent to a thunderstorm, and you will never even see it develop.

Observations suggest that approximately five percent of all thunderstorms produce a microburst.

What do you know about Microbursts?

A microburst is a strong downdraft of air, up to 6,000 ft/min [60kts], which seldom lasts more than 15-20 minutes and is typically less than one mile wide. To put it into perspective, lift at 1,000 FPM is actually 10 kts of wind in the vertical axis. As the parcel nears the ground at around 1,000 to 3,000 ft, it begins to change to a horizontal flow, creating a wind near the surface as high as 45 kts.

Microbursts occur near developing thunderstorms, or CB clouds. Some visual cues to watch for include – abnormally strong lift, unusual rain patterns, virga, blowing dust on the surface, a localized heavy rain shaft, with light winds reported on the surface, high temperature and low dew point.

What action would you take if you encountered CAT?

Adjust speed to turbulence penetration speed encountering the first moderate bumps or before if CAT has been forecast or known to exist on track. Doing so will avoid structural damage to the airplane through overstressing the airframe.

Where are you most likely to encounter Clear Air Turbulence [CAT]?

The most likely place to expect Clear Air Turbulence [CAT] is just above the central core of the jet stream near the polar tropopause and just below the core. Clear air turbulence does not occur in the core. CAT is encountered more frequently in winter when the jet stream winds are strongest. Nevertheless, CAT is not always present in the jet stream and, because it is random and transient in nature, it is almost impossible to forecast.

Clear air turbulence may be associated with other weather patterns, especially in wind shear associated with the sharply curved contours of strong lows, troughs and ridges aloft, at or below the tropopause, and in areas of strong cold or warm air advection. Mountain waves create severe CAT that may extend from the mountain crests to as high as 5000 feet above the tropopause. Curving jet streams are likely to have turbulent edges, especially those that curve around a deep pressure trough.

What is Clear Air Turbulence [CAT]?

Turbulence not associated with visible moisture. It is most commonly associated with jet streams [tropopause] or with mountain wave activity. It is more often encountered over land than over water.

What do you know about Jet streams?

Jet streams are narrow bands of exceedingly high-speed winds are known to exist in the higher levels of the atmosphere at altitudes ranging from 20,000 to 40,000 feet or more. The jet stream appears to be closely associated with the tropopause and with the polar front. It typically forms in the break between the polar and the tropical tropopause where the temperature gradients are intensified. The mean position of the jet stream, shears south in winter and north in summer, with the seasonal migration of the polar front. Because the troposphere is deeper in summer than in winter, the tropopause and the jets will nominally be at higher altitudes in the summer. Long, strong jet streams are usually also associated with well-developed surface lows beneath deep upper troughs and lows. A low developing in the wave along the frontal surface lies south of the jet. As it deepens, the low moves near the jet. As it occludes, the low moves north of the jet, which crosses the frontal system, near the point of occlusion. The jet flows roughly parallel to the front. The subtropical jet stream is not associated with fronts but forms because of strong solar heating in the equatorial regions. The ascending air turns pole ward at very high levels but is deflected by the Coriolis force into a strong westerly jet. The subtropical jet predominates in winter.

The jet streams flow from west to east and may encircle the entire hemisphere. More often, because they are stronger in some places than in others, they break up into segments some 1000 to 3000 nautical miles long. They are usually about 300 nautical miles wide and may be 3000 to 7000 feet thick. These jet stream segments move in an easterly direction following the movement of pressure ridges and troughs in the upper atmosphere.

Winds in the central core of the jet stream are the strongest and may reach speeds as great as 250 knots, although they are generally between 100 and 150 knots. Wind speeds decrease toward the outer edges of the jet stream and may be blowing at only 25 knots there. The rate of decrease of wind speed is considerably greater on the northern edge than on the southern edge. Wind speeds in the jet stream are, on average, considerably stronger in winter than in summer.

Which way does the earth turn about its axis?

[Draw on whiteboard]

What does windshear do, what is your procedure if you encounter one?

….hmmm

There is a thunderstorm on final, what do you think about?

Possible windshear and turbulence
Possible reduction in visibility
Possibility of lightning strike
Consider holding until the storm passes

What are the standard, the dry and the saturated adiabatic lapse rates?

Environmental Lapse Rate [ELR]: 1.98º C / 1000’
Dry Adiabatic Lapse Rate [DALR]: 3.0º C / 1000’ Saturated
Adiabatic Lapse Rate [SALR]: 1.7º C / 1000’

SALR varies depending on the original temperature of the rising air, and averages about 1.7º C / 1000’.

Unstable air occurs when the actual lapse rate is greater than the DALR, conditionally unstable air, when the actual lapse rate is between the DALR and the SALR, and stable air, when the actual lapse rate is less than the SALR.

Saturation: The state where the air reaches 100% humidity.

What is the Inter-Tropical Convergence Zone?

On or near the equator, where average solar radiation is greatest, air is warmed at the surface and rises. This creates a band of low air pressure, centred on the equator. This rising air comprises one segment of a circulation pattern called the Hadley Cell. The rising air is replaced by the Trade winds approaching the equator from north and south. As the trade winds meet near the equator, surface convergence and uplift take place. For this reason the equatorial band of low pressure is called the Equatorial Trough, Intertropical Convergence Zone, or the ITCZ. The ITCZ is a region of light winds, which lends it the name the doldrums. The convergence of the Southeast and Northeast Trade Winds, within the doldrums, creates a zone of Cumulus clouds and attendant shower activity. Cumulus clouds often build up to great heights. Aircraft reports have estimated tops of Cumulonimbus to be as high as 12,000m. The ITCZ varies from 20 miles to as much as 300 miles in width, and typically has an undulating conformation.

We are interested in the ITCZ because, under certain circumstances, tropical depressions on the ITCZ intensify to hurricanes. It may seem puzzling that the ITCZ can produce cyclones, when the Coriolis force is at its weakest near the equator. The answer to this puzzle lies in the fact that the ITCZ is not stationary on the equator, but migrates north and south with the seasons. The ITCZ moves north during the high-sun season of the Northern Hemisphere, and south during the high-sun season in the Southern Hemisphere. These movements are not perfectly symmetrical above and below the equator, because of the influence of landmasses, among other factors. When the ITCZ is near the equator, the convergence of surface winds along the ITCZ is likely to take the form of parallel flow, with easterly wind approaching the doldrums from both north and south. When the Trade Winds converging at the ITCZ are weak and nearly parallel to it, the ITCZ tends to narrow in width, and show little shower activity. When the ITCZ lies south of the Geographic Equator, as it does in the Western Pacific and Indian Oceans, the Northeast Trade Winds acquire a northwesterly direction after crossing the equator (because the Coriolis force changes direction below the equator!) In this situation the convergence is strong and favours the formation of a Tropical Depression When the ITCZ lies north of the Geographic Equator, the Southeast Trade Winds acquire a southwesterly direction after crossing the equator and again the convergence pattern favours the formation of a Tropical Depression. Tropical depressions tend to move from east to west at a rate of about 10 to12 knots. In most cases these disturbances are short-lived. Surface winds attending a tropical depression usually do not exceed 25 knots. The enclosing isobar has an elongated oval shape, the width of the ITCZ is greater in the region enclosed by the isobar[s], and the ITCZ exhibits a deflection away from the Geographic Equator.

There is a definite connection between the seasonal position of the Equatorial Trough and zones of hurricane formation, which is borne out by the fact that no hurricanes occur in the South Atlantic [where the trough never lies south of 5 deg S [or in the southeast Pacific [where the trough remains north of the equator]. On the other hand, satellite photographs over the northeast Pacific show an unexpected number of cyclonic vortices in summer, many of which move westwards near the trough line about 10 deg -1 deg N.

Tell me about the Monsoon.

Monsoons are cyclical wave-like air masses that occur in the sub-tropics, moving onto land from the sea during the summer and returning over water in winter. The word monsoon comes from the Arabic mausim, meaning, ‘season,’ because these storms return year after year. The term monsoon refers to large-scale seasonal reversals of the wind regime. Such seasonal wind shifts at the surface are quite widespread and occur in many regions. The Asiatic seasonal wind reversal is notable for it’s immense extent and the penetration of its influence beyond tropical latitudes. Monsoons develop as a result of changing patterns of atmospheric pressure caused by the varied heating and cooling rates of continental landmasses and oceans. The strongest and most well known monsoons are those, which affect India and Southeast Asia. The summer monsoon, which blows south-westerly across the Indian Ocean, is extremely wet. The winter monsoon, in contrast, blows northeasterly and is generally dry.

India and Southeast Asia lie in between the centres of the tropical and subtropical climate zones. For much of the year, and particularly during winter, northeast trade winds blow across the region, from subtropical high pressure to equatorial low pressure. These winds originate from the continental interiors and are generally dry. During the summer months however, the large landmasses of Asia and the Indian subcontinent heat up, generating a seasonal continental region of low pressure. Airflow reverses and wind blows southwesterly across the Indian Ocean, accumulating considerable moisture, which is deposited as heavy rainfall during the wet season from May to September. Scientists have linked the development of the monsoonal wind phenomenon over India during Earth History to the uplift of the Himalayas and the Tibetan Plateau, which occurred about 20 million years ago, when India collided into the Asian continent. The cycle continues as the cooling air creates precipitation and releases more energy. This energy then heats the air, which rises and flows back to the sea, cools, descends, and rushes back to land to replace more warm, rising air. This monsoon is centred over continental Asia.

Tell me about a cold front.

The cold front represents the leading edge of a cold air mass. The frontal zone has a steeper slope [2Ëš] and means the poor weather associated with a cold front is of shorter duration than a warm front. There may be frontal thunderstorm activity and associated precipitation. At the passage of a cold front the wind veers sharply, pressure begins to rise and temperature falls

Tell me about a warm front.

The warm front represents the leading edge of a warm air mass. The frontal zone has a very gentle slope [0.5-1˚], so cloud systems associated with a warm front [cirrus, cirrostratus and altostratus] indicate its approach 12 hours or more before it’s arrival. At the passage of a warm front, the wind veers, temperature rises and the fall of pressure is checked. The rain then becomes intermittent or ceases in the warm air and the thin stratocumulus cloud sheet may break up

Can a typhoon/cyclone cross the equator?

Yes. Once established, it can cross about 5Ëš latitude into the opposite hemisphere. In so doing it will encounter opposing Coriolis force and rapidly decrease in strength.

Which direction do they travel?

Northern hemisphere: North/northwest
Southern hemisphere: South/southwest

Which way do they turn?

That depends on the hemisphere…

Where do Typhoons form?

Formation usually occurs between 5Ëš and 15Ëš north/south latitude, over a warm ocean.

What do you know about tropical cyclones/hurricanes (typhoons)?

Most typhoon activity occurs during late summer and autumn [both hemispheres], during times of maximum northward and southward displacement of the equatorial trough. Begins life as a tropical depression and develops with favourable conditions into a tropical storm. Main energy source is latent heat from condensed water vapour. A cold-cored tropical storm is transformed into a warm-cored hurricane in association with the release of latent heat in CB towers [approximately 100-200 CB towers]. The warm core is vital to hurricane growth as it intensifies the upper anticyclone, leading to a feedback effect by stimulating the low level influx of heat and moisture, which further intensifies convective activity, latent heat release and therefore upper level high pressure. Formation of an eye is an essential part of the life cycle of a hurricane. The diameter of the eye is around 30-50km and within it, the wind is virtually calm and the cloud cover may be broken. Once developed a hurricane will usually move at 16-24km/hr in a north to north-westerly direction and a cyclone will move in a south to south-westerly direction.

Conditions for formation:

  • Ocean surface temperature of 26.5Ëšc or greater (enhances evaporation)
  • Ocean depth of 50m or more [unknown why]
  • A Low-pressure system [initial disturbance]
  • Sufficient Coriolis force [between 5Ëš and 15Ëš n/s]
  • Low values [less than about 20 kts] of vertical wind shear, between the surface and the upper troposphere.

A supply of heat and moisture combined with low frictional drag at the sea surface, the release of latent heat through condensation and removal of air aloft are essential conditions for the maintenance of a typhoon.

Tropical Classification
Tropical Disturbance: [weak area of low pressure]
Tropical Depression: [20-34 kts and a “closed” Circulation] [Storm number]
Tropical Storm [35-64 kts] [storm name]
Hurricane [65+ kts or 74+ mph]

Saffir-Simpson Scale

Maximum Winds                         Central Pressure

Category 1 65- 82 kts;               > 979 Hpa
Category 2 83- 95 kts;               965-979 Hpa
Category 3 96-113 kts;              945-964 Hpa
Category 4 114-135 kts;            920-944 Hpa
Category 5 > 135 kts;                < 920 Hpa

Tropical Disturbance 

A discrete tropical weather system of apparently organized convection – generally 200 to 600 km [100 to 300 nm] in diameter – originating in the tropics or subtropics, having a no-frontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field. Disturbances associated with perturbations in the wind field and progressing through the tropics from east to west are also known as easterly waves.

Tropical Depression A tropical cyclone in which the maximum sustained wind speed [using the U.S. 1 minute average standard] is 33 kts or less. Depressions have a closed circulation.

Tropical Storm
A tropical cyclone in which the maximum sustained surface wind speed [using the U.S. 1 minute average standard] ranges from 34 kts to 63 kts. The convection in tropical storms is usually more concentrated near the centre with outer rainfall organizing into distinct bands.

Typhoon
When winds in a tropical storm, equal or exceed 64 kts it is called a Typhoon. Typhoons designated categories 3, 4 or 5 on the Saffir-Simpson scale are known as major or intense.

What is the value of the Coriolis parameter, at the equator?

Zero

What is Coriolis parameter?

The Coriolis force is a deflecting force, which is maximum at the poles and reduces to zero at the equator. The Coriolis force always acts at right angles to the direction of the air motion to the right in the northern hemisphere and to the left in the southern hemisphere. The formula for Æ’ [Coriolis parameter] is

-2ωV sin Φ

ω = angular velocity [earths rotational velocity 15º/hr]

V = velocity of the mass

Φ = latitude [sin 0º = 0,sin 90º = 1]

What is the ICAO standard atmosphere?

+15ºc
1013.2 Hpa
2ºc /1000’ lapse rate until 36 000’ [tropopause] Isothermic at -57ºc
1 Hpa = 30’