Summary travelling disturbances

Travelling disturbances
X4 = Moisture front & line thunderstorm, coastal lows, South African
winds (Berg winds) and cut-off low
 Only occur at certain times of the year
 Arise from anticyclones
 Travel from one are to another ‘traveling’
1. Moisture front (= a zone extending northwest to southeast through the
interior of South Africa) and line thunderstorm
 Coincides with trough of LOW PRESSURE
 Warm, moist north-easterly winds from Indian Ocean (South
Indian anticyclone) converge with cooler winds from Southwest
(South Atlantic anticyclone)
 In summer the interior of South Africa is very hot which causes a
TROUGH of LOW PRESSURE over it
 Winds are drawn into this from the anticyclones (air moves from
HP to LP)
 Warm, moist north-easterly winds (SIA) blow into interior of South
Africa from north east while the cooler air from the SAA blows
from the South East; these two air masses meet along zone =
moisture front
 Warmer air rises while the colder air wedges in underneath it.
warm air rises and cools and condenses to form cumulonimbus
clouds (thunderstorms, hail and heavy rain)
 LINE THUNDERSTORM occurs along the moisture front
 Can only occur if KA had lifted to allow moist air to penetrate the
interior (summer)