Topic 2 Flashcards
Pressure belts
bands of high pressure or low pressure that surround the earth at certain latitudes, for example Equatorial low pressure belt
Where do mid-latitude cyclones form
35-70 N+S known as the polar front. Always west to east
Mid latitudes in south africa
Clod fronts only reach south africa in winter
results in winter rainfall in the western cape
Air mass
a huge mass of air, extending for hundreds of kilometres with simular humidity and temperature
Polar front
A zone where the cold polar air mass and warm tropical air mass meet. 50* S
Jet stream
a band of very strong westerly winds in the atmosphere, above 9000m which partially controls the development of midlatitude cyclones
Cold front
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
The border zone between a warm air mass and a clod air mass. Winds in the cold sector blow against the warm front.
Warm sector
The area on the ground affected by warm air in a mid-latitude cyclone
Cold sector
The area on the ground affected by cold air in a mid-latitude cyclone
The development of a mid-latitude cyclone
Initial stage: Bend forms in the polar front, low-pressure cell begins to form and winds start to deflect and blow into the low-pressure cell. Wind + strengthening + Clouds
Mature stage: The bend in the polar front deepens and the pressure gradient increases, clockwise, fronts are now formed, and sectors are formed
Partially occluded stage and occluded stage: Warm air is lighter and warmer than cold making it rise and the cold sector wedges beneath it, the cold sector taking over - partially. Occluded = Almost all warm air above
Degeneration stage: Little gust of cold air on the surface, all warm air has risen, low pressure disappears and isobars even out, weather starts clearing
Anticyclones around south africa
South Atlantic, south Indian, Kalahari. Affect climate all year, descending warm air and dry conditions most of the year
Anticyclones around south Africa in winter
Have moved northwards, both anticyclone and the mid-latitude cyclones. South Indian + South Atlantic has moved closer to the coasts. Less distance the wind needs to travel to make contact with the coast = less water vapour being picked up and less rainfall. On the interior it is clear skies, sunny weather and no rain, freezing early mornings but can be in the high 20s during midday, several months of drought, interior caused by the kalahari anticyclone. The very cold air just above the plateau, Kalahari hp warms as it subsides. Above the plateau is an inversion layer. Warm air from the Indian ocean cannot blow onto the plateau due to the inversion layer.
Inversion layer
A layer of air where temperature increases with altitude.
Anticyclones around south Africa in summer
Kalahari anticyclone has risen 500m so surface conditions don’t reflect it. The inversion layer rises above the plateau allowing the moist Indian ocean air to penetrate inland. Anticyclones have moved southwards. South Indian anticyclone blows from further away from the coast picking up lots of moist air and bringing rain to the eastern part of SA. South Atlantic blows over cold ocean currents so it doesn’t pick up a lot of moisture resulting is Western side being dry. Anticyclones elongate to form a ridge south of the country resulting in strong southeasterly winds that are funneled between mountain ranges, down valleys and down streets sometimes causing gale-force winds.
