Atmosphere, Weather and Climate
This domain tests how atmospheric processes create weather and climate: energy budgets, pressure and winds, moisture, air masses, and the controls that make climates differ. Expect questions that ask you to explain a process and apply it to a place or a numerical case.
Core rules and concepts
- The troposphere holds most weather; temperature generally falls with height there, but rises in the stratosphere because ozone absorbs ultraviolet radiation.
- Insolation varies with latitude, season and albedo. Surplus tropical energy is redistributed by winds and ocean currents.
- Wind blows along a pressure gradient, then is deflected by the Coriolis force; friction slows surface winds and turns them across isobars.
- Condensation needs cooling to dew point and condensation nuclei. Cooling by rising air gives convectional, orographic and frontal rainfall.
- Air masses take temperature and humidity from source regions. Frontal systems form where they meet. Tropical cyclones need sea-surface temperatures above about 26.5°C, low wind shear and enough Coriolis effect.
- Climate controls include latitude, altitude, continentality, ocean currents and relief.
Worked example
A sea-level parcel is 20°C with dew point 12°C. It rises. The dry adiabatic lapse rate is 10°C per 1000 m, so it reaches dew point after (20−12)/10 × 1000 = 800 m. Above that, use the saturated adiabatic lapse rate, about 6°C per 1000 m. At 2000 m, temperature is 20 − (10 × 0.8) − (6 × 1.2) = 20 − 8 − 7.2 = 4.8°C. Reasoning: condensation begins at 800 m; the remaining 1200 m uses the saturated rate.
Traps
Do not use the environmental lapse rate (about 6.5°C per 1000 m) for a rising parcel. Do not say Coriolis is strongest at the equator; it is zero there. Do not treat every cloud as rain-producing. Keep weather (short-term) separate from climate (long-term).