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
South Atlantic anticyclone
Indian Ocean anticyclone
Kalahari 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.