ATPL Fronts And Depressions Flashcards
Explain what is meant by air-mass modifications
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)
Explain what’s meant by air-mass modification by regions
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
Describe following factors associated with either ‘cold air advection’ or ‘warm air advection’ (stability)
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
Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ cloud types
- Cold advection = Cumuliform cloud
- Warm advection = Low level Stratiform cloud or fog
Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ likely precipitation
Cold advection = showers
Warm advection = drizzle
Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ - visibility reductions
Cold advection = visibility good except in showers
Warm advection = reduced visibility due to drizzle and fog
Describe the following factors associated with either ‘cold air advection’ or ‘warm air
advection’ - turbulence
Cold advection = moderate to severe turbulence
Warm advection = nil or light turbulence
Describe concepts of convergence and divergence
•(Low) Convergence = air flowing in and ascending at the surface
•(High) Divergence = air descending at the surface and diverging
Explain the vertical motions generated by convergence and divergence near the earth’s
surface and immediately beneath the tropopause
(Lows) Lower level convergence = upper level divergence
(Highs) Lower level divergence = upper level convergence
Explain the concept of vorticity and the different types
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
Explain the two components of relative velocity
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.
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
Greater the amount of moisture the greater the development of cloud/precipitation
Larger amounts of latent heat released increasing instability
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
Unstable = cumulus
Stable = layer type - stratiform
Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation:
Slope of frontal surface
Steep sloping = cumulus
Shallow sloping = stratiform
Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation
Speed of front
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
Describe the effect of the following on the intensity of fronts, and on the extent of cloud and precipitation
Temperature contrast across the front
Greater the contrast, the greater the intensity as more air will be able to rise on warm side.
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
Cold front Pressure:
Before - decrease
At - arrest or fall
After - increase
Warm front pressure
Before - decrease
At - arrest or fall
After - increase
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
Cold front -
Before - steady warm
At - abrupt decrease
After - steady cold
Warm front -
Before - steady/slight decrease
At - increase
After - little change
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
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
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
Cold front:
Before - none
At - heavy showers/hail
After - isolated showers
Warm front:
Before - Light to persistently heavy
At - drizzle
After - occasional rain/drizzle
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
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
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
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
Explain concept of occluded front
Cold front overtaking warm front
Depends on how cold air is Infront of warm front
Coldest air will be undercut everything else
Explain how convergence drives an increase in vorticity through conservation of angular momentum
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)
Outline the effect of vorticity advection on the development of mid-latitude
pressure systems
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
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
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
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
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
