ATPL Fronts And Depressions

Question 1

Explain what is meant by air-mass modifications

Answer 1

Continental = land air mass
Maritime = ocean air mass
Cold air moving to warm area = cold advection (unstable)
Warm air moving to cold area = warm advection (stable)

Question 2

Explain what’s meant by air-mass modification by regions

Answer 2

Continental arctic - land air mass from arctic
Maritime polar - ocean air mass from arctic
Maritime tropical - ocean air mass from tropics
Maritime equatorial - ocean air mass from equator
Continental Antarctic - land air mass from Antarctic

Question 3

Describe following factors associated with either ‘cold air advection’ or ‘warm air advection’ (stability)

Answer 3

K = Cold e.g PmK = Polar maritime cold
•W = Warm e.g TmW = Tropical maritime warm

•Cold air advection = cold air moving into warmer areas
•Warm air advection = warm air moving into cold areas

• Cold air warms up as it moves to warmer areas increasing instability
• warm air colds down as it moves to colder areas, increasing stability

Question 4

Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ cloud types

Answer 4

• Cold advection = Cumuliform cloud
• Warm advection = Low level Stratiform cloud or fog

Question 5

Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ likely precipitation

Answer 5

Cold advection = showers

Warm advection = drizzle

Question 6

Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ - visibility reductions

Answer 6

Cold advection = visibility good except in showers

Warm advection = reduced visibility due to drizzle and fog

Question 7

Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ - turbulence

Answer 7

Cold advection = moderate to severe turbulence

Warm advection = nil or light turbulence

Question 8

Describe concepts of convergence and divergence

Answer 8

•(Low) Convergence = air flowing in and ascending at the surface

•(High) Divergence = air descending at the surface and diverging

Question 9

Explain the vertical motions generated by convergence and divergence near the earth’s
surface and immediately beneath the tropopause

Answer 9

(Lows) Lower level convergence = upper level divergence

(Highs) Lower level divergence = upper level convergence

Question 10

Explain the concept of vorticity and the different types

Answer 10

Means rotation/spin of airmass like a river with rotating eddies.

Relative vorticity = wind velocity pattern aloft. Caused by shear (horizontal difference in speeds) or curvature (forced changed in direction which imparts a spin). Can be anti/cyclonic

Earths velocity = generated by earths spin which is always cyclonic. Stronger than relative velocity.’

Absolute velocity = earths vorticity + relative, absolute is always cyclonic

Question 11

Explain the two components of relative velocity

Answer 11

Curvature velocity - when a fluid(the air) is forced to change direction, a spin is imparted onto that fluid.

Shear velocity - vorticity generated in a straight-line flow if theres a wind speed differential in the horizontal plane. Generated most readily when a jet stream exists within the linear section of the flow between ridges and troughs.

Question 12

Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation: amount of moisture in the warm rising air

Answer 12

Greater the amount of moisture the greater the development of cloud/precipitation

Larger amounts of latent heat released increasing instability

Question 13

Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation:

Stability or instability of rising air

Answer 13

Unstable = cumulus

Stable = layer type - stratiform

Question 14

Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation:

Slope of frontal surface

Answer 14

Steep sloping = cumulus

Shallow sloping = stratiform

Question 15

Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation

Speed of front

Answer 15

Faster the front the narrower it’ll be but greater its intensity and activity

Cold fronts tract at 0.8x speed of wind 0.6 for warm

Slow front = stable stratiform
Fast = unstable cumulus

Question 16

Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation

Temperature contrast across the front

Answer 16

Greater the contrast, the greater the intensity as more air will be able to rise on warm side.

Question 17

escribe the sequence of events during the passage of an idealised cold front and
warm front (or warm sector) in both hemispheres, in terms of pressure changes

Answer 17

Cold front Pressure:
Before - decrease
At - arrest or fall
After - increase

Warm front pressure
Before - decrease
At - arrest or fall
After - increase

Question 18

escribe the sequence of events during the passage of an idealised cold front and
warm front (or warm sector) in both hemispheres, in terms of

Temperature changes

Answer 18

Cold front -
Before - steady warm
At - abrupt decrease
After - steady cold

Warm front -
Before - steady/slight decrease
At - increase
After - little change

Question 19

escribe the sequence of events during the passage of an idealised cold front and
warm front (or warm sector) in both hemispheres, in terms of

Cloud

Answer 19

Cold front:
Before - Cs or As
At - Cu,Cb, No
After - clear, isolated Cu, Cb

Warm front:
Before - Ci, Cs, As, St, Ns, Sc, Cu, Cb
At - St, Ns, Cu,Cb
After - low-level cloud may persist

Question 20

escribe the sequence of events during the passage of an idealised cold front and
warm front (or warm sector) in both hemispheres, in terms of

Precipitation

Answer 20

Cold front:
Before - none
At - heavy showers/hail
After - isolated showers

Warm front:
Before - Light to persistently heavy
At - drizzle
After - occasional rain/drizzle

Question 21

escribe the sequence of events during the passage of an idealised cold front and
warm front (or warm sector) in both hemispheres, in terms of

Visibility

Answer 21

Cold front:
Before - fair
At - very poor
After - very good, reduced in showers

Warm front:
Before - good but becoming poor in rain
At - very poor
After - fair but poor in drizzle/rain

Question 22

escribe the sequence of events during the passage of an idealised cold front and
warm front (or warm sector) in both hemispheres, in terms of

Dew point changes

Answer 22

Cold front:
Before - no change
At - increase
After - lower then in advance of front

Warm front:
Before - slight increase
At - steady
After - higher than in advance of front

Question 23

Explain concept of occluded front

Answer 23

Cold front overtaking warm front
Depends on how cold air is Infront of warm front
Coldest air will be undercut everything else

Question 24

Explain how convergence drives an increase in vorticity through conservation of angular momentum

Answer 24

Angular momentum = airmass x RPM x Radius^2

where k is constant and air mass can’t change its size so RPM and radius can change due to absolute velocity.

RPM increase = radius reduce (convergence)
RPM decrease = radius increase (divergence)

Question 25

Outline the effect of vorticity advection on the development of mid-latitude
pressure systems

Answer 25

Vorticity advection = horizontal movement of spinning air aloft

•If spinning air aloft links up with spinning air at surface it will create either a high or a low depending on if its convergence or divergence

•Most highs and lows in mid latitudes created this way

Question 26

With respect to depressions of the Southern Hemisphere outside the tropics, describe the development and associated cloud

of the high mid - high latitude depression, where upper level divergence dominates the formation process

Answer 26

If upper-level divergence dominates the lows will have very strong upward vertical motion
•Extensive cloud band will form creating cold fronts and warm fronts with mostly unstable clouds

Question 27

With respect to depressions of the Southern Hemisphere outside the tropics, describe the development and associated cloud of the

sub-tropical depression, where advection of warm moist air and latent heat release dominate the formation process

Answer 27

Warm moist air moving towards the poles from tropics/subtropics
•Radius on which it rotates reduces towards the poles
•Creates low level convergence
•Will be enhanced further by release of latent heat
•Unstable cloud