Download 1. Ocean Currents 2. Altitude of the Plateau 3

SUBTROPICAL
ANTICYCLONES AND
RESULTANT WEATHER OVER
SOUTH AFRICA
Major Factors Influencing
South Africa’s Climate
1.
2.
3.
-
Ocean currents
Altitude of the plateau
High pressure systems
SAA
SIA
KHP
1. Ocean Currents
2. Altitude of the Plateau
3. High Pressure Systems
THE IMPACT OF THE
ANTICYCLONES
Kalahari HP
SAA
SIA
• Semi- permanent and semi-stationary feature
• Changes are seasonal – linked to the seasonal shift of the ITCZ and
changes in surface temperatures
• Clear, stable weather
• Air moves anticlockwise around the system
• Cool, dry air moves onto the western and southern coasts of SA
• May deflect mid-latitude cyclones away or towards the coast.
• When ridges behind a cold front, weather along that front will
intensify
SOUTH INDIAN
ANTICYCLONE
• Semi-permanent and semi-stationary
• Air moves anticlockwise around the system and
feeds warm, moist air into SA from the northeast
• When the system is located close to SA, there is
a greater chance of moist winds reaching the
western part of the country
• Over the interior, especially during the winter
months (in reality it is part of the SAA and SIA)
• More intense during winter and weakens in summer
In WINTER MONTHS
• Temperatures are lower, cool, dense air sinks onto the interior
• As the air sinks it is compressed and heated adiabatically
• It causes the lower layers to be warmer than those above them and
an inversion is formed
• As a result of the air sinking, the pressure system ’rests’ on the
escarpment. It acts as a lid and prevents warm, moist air moving
from the Indian Ocean into the interior
• It causes the interior to experience dry winters
In SUMMER
• Air is warmer and the system is less intense
• Inversion occurs above the level of the escarpment
• Thermal lows that develop in the interior also causes
the inversion to occur at a higher altitude
• Moist air from the Indian Ocean can flow into the interior .
• This results in summer rainfall
Line Thunderstorms
LINE THUNDERSTORMS - SUMMER
WARM
MOIST
AIR
COLD
DRY
AIR
H
H
Berg Winds
SOUTH AFRICAN BERGWIND
Anti clockwise
circulation
H
High pressure
in interior
Descending
air heated
Danger:
Veldfires
Warm dry wind at coast
Low pressure
L over sea
Synoptic Chart Revision
It is a Winter chart if…
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Date (April – August)
Low temperatures over interior (use examples)
Low dew point temperatures in interior – dry air
Little or no cloud cover over interior (PTA)
Cloud cover and rain over Cape Town –
Mediterranean Climate
Berg wind conditions – Pre frontal/coastal LP
Cold front over interior
No Tropical Cyclones
High Pressure over interior
Winter
WINTER WEATHER MAP
It is a Summer chart if…
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Date (October – February)
High temperatures over interior
Dew point and maximum temperatures in
interior within 5 degrees of each other – moist
air
Cloud cover over interior
Little or no cloud cover and rain over Cape
Town – Mediterranean Climate
No cold front over interior
Presence of a tropical cyclone
Low Pressure over interior
Summer
SUMMER WEATHER MAP
THUNDER STORM
HIGH PRESSURES
FURTHER SOUTH