chapter 1 Flashcards
mid-latitude cyclones
general characteristics of a mid-latitude cyclone
o Forms between 30-60 N/S
o Moves eastward
o Has two fronts (warm and cold)
o Large diameter
o Lasts between 4-14 days
o Steered by westerlies
o Affects SA in winter
Alternate names
o Extra tropical cyclone
o frontal depression
o temperate cyclone
Conditions for formation
Frictional drag is caused by the difference in temperature and speed of the two air masses.
Air masses must move opposite to each other and parallel.
Warm subtropical air must meet cold polar air at the polar front.
Stages in formation
o Initial:
* Cold polar air and warm tropical air move parallel to each other but in opposite directions
at the polar front.
o Wave formation:
* Frictional drag takes place.
* Warm air becomes uplifted.
* Fronts begin to form as air converges to the centre low pressure.
o Mature:
* Wave deepens.
* Cold and warm sectors and fronts fully developed.
* Warm air moves up steep pressure gradient of cold front to form towering cumulonimbus
clouds. (heavy rain over a small area)
* Warm air moves up gentle pressure gradient of warm front to form a broad band of
stratus clouds. (light rain over a large area)
o Occlusion:
* Cold front catches up to the warm front at the apex. (apex is the shortest distance between
the fronts)
* Cold front occlusion: warm air moves up the cold front. (cold front on the ground)
* Warm front occlusion: cold air moves up the warm front. (warm front on the ground)
Weather associated with Mid-latitude cyclones
o Cold front weather:
* Low air temperature
* Thunderstorms and hail
* Rise in air pressure
* Low humidity
o Warm front weather:
* Rising air temperature
* Soft rains
* Drop in air pressure
* High humidity
Cyclone families
o Mid-latitude cyclones form in groups.
o Up to 5 can pass through a certain area in quick succession.
Impact of mid-latitude cyclones
o Rain:
✓ Water for vineyards and deciduous fruits
Flooding
o Snow:
✓ Tourist attraction
Crop damage
o Storms:
A threat to fishermen at sea
Precautionary and management strategies
o Build high
o Efficient drainage systems
o Enclose livestock
o Sufficient grain
o Update weather systems
o Secure boats
What is a warm sector?
The area on the ground affected by warm air in a mid-latitude cyclone.
What is the cold sector?
The area on the ground affected by cold air in a mid-latitude cyclone.
Cold front definition
The border zone between a cold air mass and a warm air mass. Winds in the cold sector blow against the cold front.
Warm front definition
The border zone between a warm air mass and a cold air mass. Winds in the warm sector blow against the warm front.
What is backing?
A change in direction of the winds in an anticlockwise direction, for example from north to northwest.
What is veering?
A change in direction of the winds in a clockwise direction, for example from south to southwest.
Cold front occlusion
An occlusion where the overtaking cold air is colder than the cold air ahead of it.
