ZIMSEC A Level · Geography · Form 5
The energy budget
Incoming solar radiation (insolation) is absorbed, reflected (albedo) or scattered; the Earth radiates long-wave energy. The greenhouse effect traps outgoing radiation. There is an energy surplus in the tropics and a deficit at the poles, transferred by winds and ocean currents.
Atmospheric circulation
The tricellular model: Hadley, Ferrel and polar cells. Rising air at the Inter-Tropical Convergence Zone (ITCZ) brings heavy rain; sinking air near 30° creates high pressure and deserts (Kalahari, Namib).
Zimbabwe's climate
- Summer rainfall from the southward movement of the ITCZ (November–March) and moist easterly flows from the Indian Ocean.
- Relief rainfall in the Eastern Highlands; rain-shadow effect in the lowveld.
- Variability: droughts associated with El Niño, wetter years with La Niña.
Atmospheric stability
Stable air (environmental lapse rate less than the saturated adiabatic lapse rate) resists uplift; unstable air rises and forms cumulonimbus clouds and thunderstorms.
Tropical cyclones
Form over warm oceans (above about 26–27 °C) away from the equator (Coriolis effect needed). Strong winds, storm surges and torrential rain – Cyclone Idai (2019) caused floods and landslides in Chimanimani and Chipinge.
Climate change
Enhanced greenhouse effect from fossil fuels and deforestation; impacts include rising temperatures, more erratic rainfall and more frequent extreme events. Responses: mitigation and adaptation.
Check yourself
- What is albedo?
- Why do deserts form near 30° N and S?
- State two conditions needed for a tropical cyclone to form.
Show answers
- The proportion of incoming radiation reflected by a surface.
- Air sinks in the descending limb of the Hadley cell, creating high pressure and dry conditions.
- Any two: sea temperature above about 26–27 °C, distance from the equator (Coriolis), low wind shear, moist unstable air.
Questions about this topic (0)
No questions about this topic yet.
Sign in or create a free account to join in.