Mid-latitude cyclones
AKA temperate cyclones, extra-tropical
General characteristics cyclones, frontal depressions or wave
travelling low pressure systems cyclones
form when warm, subtropical air masses (subtropical
westerly winds) meet with cold, polar air masses (polar
easterly winds) along the polar front (60 degree line of
latitude)
mostly affect South Africa in winter when the pressure belts
have shifted northwards
the cold front of a mid-latitude cyclone can extend up to
1200km over the interior of the country
form to the south west of South Africa and move in an
easterly direction (from west to east) driven along by the
upper atmospheric jet streams which are located near the
tropopause and the surface westerly winds
may occur in groups or families cold front: the leading edge of
cold air mass
southern hemisphere = clockwise circulation
warm front: the leading edge of
northern hemisphere = anti-clockwise circulation a warm air mass
polar front: the boundary/zone
separating cold polar air and
warm tropical air
jet streams: fast flowing narrow
air currents found near the
tropopause. The major jet
streams are westerly winds
moving from west to east
tropopause: the boundary
between the troposhere and
stratosphere
, Areas where mid-latitude cyclones form
Mid-latitude cyclones form in the mid-latitudes, approximately 30 to
75 degrees north and south of the Equator. They develop at the polar
front, usually over the sea, which is found at 60 degrees North and
South.
Summer Winter
shift of the The polar front boundary shifts The polar front boundary shifts
pressure southwards, in conjunction with northwards in conjunction with
belts the shift of the pressure belts. the shift of the pressure belts.
The cold front is now too far
south to affect the South African
weather
Location of
the sub-
tropical
high
pressure
belt
AKA temperate cyclones, extra-tropical
General characteristics cyclones, frontal depressions or wave
travelling low pressure systems cyclones
form when warm, subtropical air masses (subtropical
westerly winds) meet with cold, polar air masses (polar
easterly winds) along the polar front (60 degree line of
latitude)
mostly affect South Africa in winter when the pressure belts
have shifted northwards
the cold front of a mid-latitude cyclone can extend up to
1200km over the interior of the country
form to the south west of South Africa and move in an
easterly direction (from west to east) driven along by the
upper atmospheric jet streams which are located near the
tropopause and the surface westerly winds
may occur in groups or families cold front: the leading edge of
cold air mass
southern hemisphere = clockwise circulation
warm front: the leading edge of
northern hemisphere = anti-clockwise circulation a warm air mass
polar front: the boundary/zone
separating cold polar air and
warm tropical air
jet streams: fast flowing narrow
air currents found near the
tropopause. The major jet
streams are westerly winds
moving from west to east
tropopause: the boundary
between the troposhere and
stratosphere
, Areas where mid-latitude cyclones form
Mid-latitude cyclones form in the mid-latitudes, approximately 30 to
75 degrees north and south of the Equator. They develop at the polar
front, usually over the sea, which is found at 60 degrees North and
South.
Summer Winter
shift of the The polar front boundary shifts The polar front boundary shifts
pressure southwards, in conjunction with northwards in conjunction with
belts the shift of the pressure belts. the shift of the pressure belts.
The cold front is now too far
south to affect the South African
weather
Location of
the sub-
tropical
high
pressure
belt
