Subtropical Anticyclones Grade 12 Climatology Subtropical Anticyclones

Subtropical Anticyclones Cells of high pressure Subtropical areas are found between Tropic of Capricorn/Cancer and 40°N/S. They tend to bring clear, calm weather. In an anticyclone air descends and pressure increases. This brings very light winds which blow out from the centre in an anti-clockwise direction in the S.H. H

Planetary wind blow out of and around high pressure cells towards low pressure cells along the pressure gradient. Coriolis force deflects these winds to the left in the SH.

Pressure Cells Around SA Kalahari anticyclone Indian Ocean anticyclone South Atlantic anticyclone

Anticyclonic influence on climate in winter S.A.A, S.I.A and Mid-latitude cyclones all move further northwards. In the northern hemisphere summer the sun is directly overhead causing the heat distribution and pressure belts to move northwards. S.A.A & S.I.A move closer to the coasts. Winds travelling out of these cells have a shorter distance to travel, therefore they pick up less moisture and bring less rain at this time of year.

Weather in the Interior (Winter) We see clear skies, sunny weather and no rain. Temperatures range from freezing to mid twenties. We often see very little rain or drought for a few months. These conditions are caused by the Kalahari anticyclone. Inversion Layer: a layer of air where temperature increases with altitude.

Weather in summer Kalahari .A. has risen verticaly by about 500m Hot conditions in summer cause a low pressure at the surface – this is why we see a low pressure. The inversion layer rises with the K.A.A. this allows moist air from the Indian Ocean to penetrate inland = summer rain. Pressure belts and S.A.A & S.I.A have shifted further southwards. S.A.A & S.I.A have shifted further from the coast. Winds travel further and pick up moisture. Warm current = more moisture = more rain

Position of the Kalahari High in Winter

Position of the Kalahari High in Summer

The Southeaster S.A.A moves south and often elongates to form a ridge south of the country. This produces south easterly winds over the cape. The wind can be funnelled through valleys, streets and can be very strong. Wind is known as the Cape Doctor as it blows in and can cool off the cape and blow pollution away.