Fronts And Depressions

Question 1

Describe a cold front

Answer 1

•Polar front theory = Warm air-mass meets cold air-mass and rotates around low

When cold air undercuts slower moving warm air
•Cold air lifts the less dense warm air in front
•Frontal lifting creates cloud
•Formation of cloud releases latent heat increasing instability therefore cumuliform cloud
•20 – 30kts and slope 1:80

Question 2

Describe a warm front (warm sector)

Answer 2

Warm moist airmass is forced to rise over slower moving cold air
•Rises slower than in cold front as slower moving and more widespread
•Therefore more stable and often stratiform type cloud
•10 – 15kts and slope 1:150

Question 3

Describe occluded fronts

Answer 3

Cold occlusion - colder air catching cold air

Warm occlusion - cold air catching colder air

Question 4

Describe stationary fronts

Answer 4

Cold air opposed by warm air
Weak
Remains of decaying frontal system
Less than 5kts

Question 5

Outline characteristics of mid-high latitude depressions (‘lows’)

Answer 5

Move west to east
Moist sub-tropical air masses meet cold polar air masses creating what’s known as polar front depressions

Question 6

Outline characteristics of sub-tropical depressions

Answer 6

More common than tropical cyclones, Occur when system moves over warm water. Not counted as mid latitude or equatorial depressions and they tend to form warm fronts

Question 7

Outline characteristics of tropical cyclones

Answer 7

Move at 10-15kts
64+ kt winds
Life cycle of up to 2 weeks

Question 8

Describe development and aspects of importance to aviation of lee depressions.

Answer 8

Lee of mountain sheltered from the wind
Creates low pressure in the lee
Bad wx on the lee side of mountain
Severe turbulence like the wake of an aircraft

Question 9

Describe development of thermal lows

Answer 9

Usually develop over land in summer
Conduction causes convection which increases instability
Creates turbulence due to thermals
Possible thunderstorms and hail if Cbs develop
Reduces density of air

Question 10

Describe development and aspects of importance to aviation of depressions crossing a mountain barrier

Answer 10

•Surface level depression stops as it runs up against mountain but above mountain the depression continues to move around and then it creates a new low level depression on leeward side
•

Poor IMC weather conditions on both sides of mountain, fohn like conditions form