1. Two colums of air that weigh the same, one at the pole, one at the equator.
2. The tropopause is higher at the equator, at any given altitude the air is warmer and has a higher pressure.
3. This causes a flow from the equator to the pole, which is bent by corriolous to make a westerly wind.
4. As the greatest pressure gradiant is found at the tropopause, this is where the strongest wind will be.
The Subtropical Jet is found on the poleward side of the Hadely cell
The Polar jet is found on the polar side of the ferrel cell
Both Jets move poleward in summer, the polar jet is more mobile then the subtropical.
Which Jetstream is nearest to HK?
The Sub Tropical Jet
-Environmental Lapse Rate
-quantified as the change in temperature per thousand feet of altitude.
-ISA ELR is 1.98°C per 1000'.
-measured by ascending a thermometer through "still" air
Dry Adiabatic Lapse Rate
The rate at which a rising non-saturated parcel of air cools due to expansion as it rises
Normally about 3°C per 1000'
Saturated Adiabatic Lapse Rate
The rate at which a rising saturated parcel of air (cloud) cools due to expansion as it rises
Normally about 1.5°C per 1000'
Stability is when air is forced to rise it will return to its original altitude. Big consequence is lee waves or mountain waves downwind of large obstacles to the flow.
-When the ELR is less than the SALR the air is stable. ie ELR<1.5c/1000ft
-When the ELR is greater the DALR air is unstable ie ELR>3c/1000ft
-When the ELR is between the SALR and the DALR the air is conditionally stable. ie ELR - 1.5c-3c/1000ft.
When DALR is greater than the ELR, and the SALR is less that the ELR.
ELR = 2°/1000'
DALR = 3°/1000'
SALR = 1.5°/1000'
In this scenario, dry air is stable, but once saturated, becomes unstable
Unstable air encourages vertical movement of air. Any parcel of air that is lifted, will continue to rise until it reaches an altitude at which it's temperature equals the temperature around it.
When the temperature in the atmosphere decreases faster than 3 degrees Celsius per thousand feet, the atmosphere's absolutely unstable.
When the ELR is greater then the DALR
-56.5c @ 36,000ft
Temp = -56 @ FL310 what is ISA deviation?
ISA Temp = 15-(31x2) = -47°
-56 is 9 deg cooler than -47
Deviation is -9°
Identify Jetstream, speed of jetstream, CB's, tropopause. define XXXX and triangles
Identify Isobars, gradient meaning, low pressure system, wind direction.
Elevation 600ft and QFE is 998, what is QNH?
Cold Front passes, will Altimeter over read or under read?
Cold Front passes, will wind back or veer?
Southern Hemisphere- Back
Northern Hemisphere - Veer
Warm front, will wind back or veer?
Southern Hemisphere- Veer
Northern Hemisphere - Back
Changes are far less drastic than passage of cold front
Weather in a warm front? Icing? Rain? Snow?
Snow & freezing rain.
Freezing rain can cause heavy icing as supercooled water forms ice upon contact with aircraft
Ceiling and Visibility OK. Used in a METAR
1. No cloud below 5000' or MSA whichever is Higher
2. Vis greater then 10Km
3. No precipetation, thunderstorms, sandstorm, duststorm, shallow fog or low drifting dust, sand or snow occurring.
Define Fohn wind
Warm, dry airmass moving down the lee side of a mountain as a result of humid air rising and condensing on the front side of the mountain.
Cooled at a low rate by rising at SALR, then heated at a high rate by descending at DALR.
Define Katabatic wind
A katabatic wind is a down-slope wind that develops as air cools in contact with cold ground and slips down the side of the hill
Define Anabatic wind
Anabatic wind moves up a slope as a result of conductive heating of a higher airmass.
An example is upper cliff faces in a valley heating up with morning sun. As the local air rises, the valley air will flow upwards to replace that air.
Windsheer recovery technique
1. Full power
2. Best rate of climb Attitude.
3. Don't change configuration until clear.
Partial Fog(covering part of the Aerodrome)
Name the three Cells
1. Warm water above 26.5c to depth of 50m
2. More then 500Km from the equator
3. Unstable atmosphere
4. A low level disturbance(eg ITCZ, front)
5. Less then 20Knts of windshear between ground and tropopause.
Hong kong typhoon season