*G12- Subtropical Anticyclones Flashcards
SA lies between
22 and 35*S
SA’s climate dominated by
Belt of subtropical highs that circle earth at 30*S
3 cells of high pressure in Southern Africa
South Atlantic
South Indian
Kalahari
Caused by
Air subsiding from tropical and mid latitude cells
Bring (a and thus (b
(a descending, dry warming air
(b clear skies and sunshine
Winds blow around the high
Anti-clockwise
Anti cyclone positions change all the time, resulting in
Changing seasonal climate and changing weekly/daily weather
Influence on climate in winter *2
*SIA and SAA move north (sun overhead, weather systems north, blah blah blah)
*closer to coasts so less WV is picked up thus less rain, clear skies and sunny weather
Temperature range in winter
Freezing in morning to high 20s during the day
Why does the KAC bring that temp range *4
*cold air immediately above plateau
*dry air from KAC warms up as it subsides
*above plateau there’s and inversion layer, rising air cannot penetrate it
*warm moist air from IO cannot blow onto plateau therefore drought in the interior
Inversion layer
Layer where temp increases with altitude
Influence on climate during summer *5
*interior is hot so low pressure
*KAC rise 500m
*inversion layer rises with KAC allowing warm moist air from IO to penetrate inland
*SAA and SIA move south
*SAA and SIA move further from coasts so winds blowing out have greater distance to land
SAA and SIA move further from coasts so winds blowing out have greater distance to land *2
*winds from SIA are warmed by Mozambique current > pick up moisture > rain to east side
*winds from SAA cooled by Benguela current > don’t pick up moisture > no rain
Southeaster *4
*in summer SAA moves south and elongates to form a ridge south of SA
*strong south easterlies over cape peninsula and southern cape
*winds reach land and are funnelled between mountain ranges, down valleys and down streets
*gale force winds
Travelling disturbances associated *4
*moisture front and line thunderstorms
*coastal low
*berg winds
*cut off low
Moisture front and line thunderstorms *2
*Warm moist north easterly winds meet cool winds from south east at moisture front which coincides with trough of low pressure
*warm air is unstable, rises and condenses into cumulonimbus clouds and bring hail amd heavy rain
Why are they called line thunderstorms
They occur on the line of a moisture front
Line thunderstorms not the same as conventional rain
only occurs if KA rises and allows warm moist air to reach interior
Sometimes delayed rain
Moisture front *2
*zone extending from NW to SE through SAs interior
*warm moist north easterly winds blow with cooler winds from south west
Coastal low *4
*move w to e during autumn and winter
*clockwise air circulation
*onshore flow behind low- clouds and fog
*offshore flow ahead low- clear warm weather
Berg wind (definition)
Local wind that blows down escarpment from plateau to coast, bringing hot dry weather
Ridge
Oblong shaped area of high pressure extending from anticyclone
Winds blow along the pressure gradient (by cold front and KA) from…
High pressure to low pressure
Winds blow down escarpment to coast and
Warm up adiabatically, 30*+ in coastal towns
Berg wind symbols *4
*clear sky
*max temp
*low DP
*low wind speed
CF symbols *3
*overcast
*cold
*wet
Cut off low *3
*SAA forms ridge behind behind CF, cutting it off
*cold moist air flows in from SW
*very cold weather and snow
What causes a steep PG
LP cell and CF ahead of AC
Why the southeaster blows over southern cape in summer only *3
*SAA moves south in summer
*ridges south of country
*winds blowing out are southeasterly
Are winds blowing out AC always southeastly
No, depends on one’s position in relation to high pressure
Weather brought by traveling disturbances *5
*Cut off low- very cold weather with heavy rain and snow
*Berg wind- warm dry wind
*Moisture front- humid rising air and cumulonimbus
*Coastal low- offshore air (clear warm weather)
*Line thunderstorms- clouds and heavy rain
