Weather, Climate, and the Atmosphere
Weather, Climate, and the Atmosphere
This domain tests atmospheric structure, humidity, winds, air masses and fronts, severe weather, and the factors that control climate.
Core rules and concepts
- Dry air is about 78% nitrogen and 21% oxygen. Layers: troposphere (weather), stratosphere (ozone), mesosphere, thermosphere.
- In the troposphere, temperature generally decreases with altitude, and pressure decreases with altitude.
- Winds blow from high to low pressure; the pressure-gradient force starts motion, the Coriolis effect deflects it, and friction slows surface winds. Winds are named for the direction they come from.
- Relative humidity = actual water vapor ÷ maximum capacity × 100%. Dew point is the temperature at which air saturates; cloud base forms where rising air cools to the dew point.
- Cold fronts are steep and produce cumulonimbus storms; warm fronts are gentle and produce layered clouds.
- Climate controls include latitude, elevation, proximity to water, ocean currents, prevailing winds, and mountain barriers.
Worked example
Surface air is 20°C with a dew point of 12°C. The dry adiabatic rate is 10°C per 1000 m, and the dew point decreases about 2°C per 1000 m. The 8°C gap closes at 8°C per 1000 m, so the cloud base is at 1000 m.
Traps that cost marks
- Assuming 100% relative humidity always means rain; saturation alone does not guarantee precipitation.
- Forgetting that high pressure generally means sinking air and clear weather.
- Naming wind by where it is going rather than where it came from.
- Mixing up the environmental lapse rate with adiabatic rates.