Module 4: Introduction to South Africa's Weather and Climate

Equatorial Regions in Africa

• Located near the equator, primarily in central Africa and the southern coast of West Africa
• Temperature characteristics:
• Hot temperatures prevail throughout the year
• Average temperatures range between 25°C and 27°C
• Limited temperature variation, with only a 3°C annual range
• Humidity and rainfall:
• Equatorial areas are highly humid
• Experience over 1,500 millimeters of rainfall annually
• Afternoon convection storms are the most common form of precipitation

Tropical Regions Around the Equator

• Encircle the equator, with major locations in East Africa, the Congo, and parts of the Sub-Saharan belt
• Adiabatic cooling:
• Rising air becomes cool
• Heat energy is used as the air expands, and pressure decreases
• Adiabatic cooling: process where rising air cools at 1°C for every 100 meters of ascent
• Dry Adiabatic Lapse Rate: the term for the rate at which rising air cools
• Effect on water vapor:
• Cooling air can hold less water vapor
• Condensation may occur as a result
• Cloud formation and rainfall may follow the condensation process

Effects of Subsidence and Convergence on African Rainfall

• Convection currents at the ITCZ:
• Strong convection currents near the equator create areas of low pressure
• Tropical Easterlies and convergence:
  • Strong winds from the north and south converge on the equatorial low-pressure belt
  • These converging winds are known as tropical easterlies
• Intertropical Convergence Zone (ITCZ):
  • The convergence zone formed by tropical easterlies is called the Intertropical Convergence Zone or ITCZ
• Effect on air and rainfall:
  • Hot air from the equator rises due to temperature
  • Convergence of tropical easterlies at the ITCZ causes air to rise, cool, and condensate
  • This process in equatorial regions leads to rainfall

High-Pressure Belts Between 15° and 30° Latitude

• Subsiding Air and High-Pressure Belts:
• Subsiding air creates high-pressure areas between 15° and 30° latitude
• These high-pressure areas are known as subtropical high-pressure belts
• Condensation and dry conditions:
• Condensation does not occur in the descending, warming air
• This lack of condensation results in dry conditions between the latitude points
• Impact on Sahara Desert:
• The subsiding air in this region contributes to the creation and persistence of the Sahara Desert in North Africa

Convergence at the Polar Front

• Air Mass Convergence and Polar Front:
• Air masses converging at the polar front lead to the rising of air
• Mid-Latitude Cyclones and Westerly Winds:
• Mid-latitude cyclones form due to the rising air and are carried by the westerly winds
• Formation of Cold Fronts:
• Cold fronts are caused by these mid-latitude cyclones
• Cyclonic Rain in Western Cape and North Africa:
• The Western Cape in South Africa experiences cyclonic (or frontal) rain during winter
• Similar conditions occur between 30° and 40° N in North Africa

Ocean's Impact on African Temperature

• Wind-Driven Ocean Currents:
• Winds continually blowing over the ocean surface create a dragging action, leading to the formation of ocean currents
• Warm and Cold Air Above Ocean Currents:
• Air above a warm ocean current is warm, while air above a cold ocean current is cold
• Influence on Coastlines:
• Prevailing winds carry warm and cold air from their respective ocean currents toward the land
• Ocean currents influence the coastlines they flow past
• Example in South Africa:
• In South Africa, the warm Agulhas Current flows down past the east coast, while the cold Benguela Current flows up the west coast

Ocean's Impact on African Rainfall

• Evaporation from Ocean as Main Precipitation Source:
• The primary source of precipitation over Earth's landmasses is the evaporation of water from the ocean
• Onshore Winds and Moisture Transport:
• Onshore winds from the sea to the land carry moisture to coastal areas, making inland places generally drier
• Effect of Warm Ocean Currents:
• Warm ocean currents lead to warmer air above them, capable of holding more water vapor, resulting in more rain in warm ocean maritime climates
• Effect of Cold Ocean Currents:
• Cold ocean currents, with colder air above them, hold less water vapor, causing less rain in colder maritime climates
• Examples from South Africa:
• The Kalahari Desert is influenced by the cold Benguela climate, leading to limited moisture and the formation of mist or fog
• The Namib Desert's existence is attributed to the cold Benguela Current
• The east coast of South Africa and Mozambique receives more rain due to the warm Agulhas Current