Subtropical
Subtropical anticyclones
anticyclones &
&
associated
associated weather
weather conditions
conditions
Location of the high pressure cells that affect South
Africa
The high pressure cells (aka anticyclones) that affect South Africa occur along the sub-
tropical high pressure belt located at approximately 30°S.
High pressure cells that are present all year round:
The South Atlantic High located off the west coast of South Africa over the Atlantic
Ocean
The South Indian High located off the east coast of South Africa over the Indian Ocean
The high pressure cell which only effects South Africa in winter is the Continental High - also
known as the Kalahari High. This cell is located over the interior of South Africa
These 3 high pressure systems are greatly influenced by the seasonal shift of the pressure
belts and therefore their positioning and intensity will vary from summer to winter. The
pressure belts shift due to the changing of the seasons
General characteristics of these high pressure cells
Winter Summer
Cooler, stable subsiding air causes the Warmer, unstable ascending air causes
pressure cells to strengthen and they the pressure cells to weaken and they
are found closer to the land are found at a higher altitude
The pressure belt shift causes the The pressure belt shift causes the cells
migrate northwards in winter to migrate southwards in summer
, ridge: an extension of a high
A ridge is said to happen when the high pressure cell
pressure cell when the isobars
extends behind a passing cold front in winter or
extend along the east-west axis
around the southern tip of South Africa in summer
South Atlantic High(SAH)- this is a high pressure cell found off the west coast of southern
African over the Atlantic Ocean. It is associated with cooler, denser subsiding air
Winter Summer
The SAH may ridge behind a mid-latitude The SAH moves slightly southwards and
cyclone. Airflow behind the mid-latitude may ridge around the southern tip of South
cyclone is south westerly and the weather Africa. It will bring general rainfall tot eh
will clear from this direction as well south-east coast (George and Knysna)
South Indian High (SIH) - this is a weaker high pressure cell found off the east coast of southern
Africa over the Indian Ocean. It is associated with warm, moist sub-tropical air
Winter Summer
The SIH is weaker and therefore allows warm,
The SIH has a blocking effect as it
moist maritime air to flow into the interior. It
advances towards the coastline. It is
has a blocking effect on the movement of mid-
more intensely developed and therefore
latitude cyclones. It may also prevent tropical
does not allow moist maritime air to be
cyclones from moving southwards and hence,
fed into the interior
tropical cyclones may move westwards over
the land or move out to sea
Subtropical anticyclones
anticyclones &
&
associated
associated weather
weather conditions
conditions
Location of the high pressure cells that affect South
Africa
The high pressure cells (aka anticyclones) that affect South Africa occur along the sub-
tropical high pressure belt located at approximately 30°S.
High pressure cells that are present all year round:
The South Atlantic High located off the west coast of South Africa over the Atlantic
Ocean
The South Indian High located off the east coast of South Africa over the Indian Ocean
The high pressure cell which only effects South Africa in winter is the Continental High - also
known as the Kalahari High. This cell is located over the interior of South Africa
These 3 high pressure systems are greatly influenced by the seasonal shift of the pressure
belts and therefore their positioning and intensity will vary from summer to winter. The
pressure belts shift due to the changing of the seasons
General characteristics of these high pressure cells
Winter Summer
Cooler, stable subsiding air causes the Warmer, unstable ascending air causes
pressure cells to strengthen and they the pressure cells to weaken and they
are found closer to the land are found at a higher altitude
The pressure belt shift causes the The pressure belt shift causes the cells
migrate northwards in winter to migrate southwards in summer
, ridge: an extension of a high
A ridge is said to happen when the high pressure cell
pressure cell when the isobars
extends behind a passing cold front in winter or
extend along the east-west axis
around the southern tip of South Africa in summer
South Atlantic High(SAH)- this is a high pressure cell found off the west coast of southern
African over the Atlantic Ocean. It is associated with cooler, denser subsiding air
Winter Summer
The SAH may ridge behind a mid-latitude The SAH moves slightly southwards and
cyclone. Airflow behind the mid-latitude may ridge around the southern tip of South
cyclone is south westerly and the weather Africa. It will bring general rainfall tot eh
will clear from this direction as well south-east coast (George and Knysna)
South Indian High (SIH) - this is a weaker high pressure cell found off the east coast of southern
Africa over the Indian Ocean. It is associated with warm, moist sub-tropical air
Winter Summer
The SIH is weaker and therefore allows warm,
The SIH has a blocking effect as it
moist maritime air to flow into the interior. It
advances towards the coastline. It is
has a blocking effect on the movement of mid-
more intensely developed and therefore
latitude cyclones. It may also prevent tropical
does not allow moist maritime air to be
cyclones from moving southwards and hence,
fed into the interior
tropical cyclones may move westwards over
the land or move out to sea
