Atmosphere, Weather, Climate, and Oceans
This domain examines atmospheric structure and composition, the processes that produce weather, the controls on climate, and ocean circulation. Expect questions on fronts, stability, Coriolis effects, climate feedbacks, and interpretation of simple atmospheric calculations.
Atmosphere and Circulation
The troposphere contains most atmospheric mass and weather; temperature decreases with altitude until the tropopause. The stratosphere contains ozone that absorbs ultraviolet radiation. Pressure decreases with altitude. Unequal heating drives convection; the Coriolis effect deflects moving air to the right in the Northern Hemisphere and left in the Southern without changing speed. Global cells produce trade winds, westerlies, and polar easterlies; the ITCZ marks convergence near the equator.
Weather Systems
Air masses take on temperature and moisture from source regions. Cold fronts are steep and produce short, intense precipitation; warm fronts are gentle and broad. Low-pressure cyclones have converging, rising air and clouds; high-pressure anticyclones have sinking, diverging air and clear skies. Hurricanes require warm ocean water, moisture, and Coriolis; they weaken over land.
Climate and Oceans
Climate is long-term statistical weather. Controls include latitude, altitude, continentality, ocean currents, and albedo. The greenhouse effect is natural and essential; enhanced greenhouse warming is a separate issue from ozone depletion. Ocean surface currents are wind-driven; thermohaline circulation is density-driven. Upwelling brings cold, nutrient-rich water.
Worked Example: Lifting Air Parcel
An air parcel at 20°C with dew point 10°C rises. The dry adiabatic lapse rate is 10°C/km; it saturates after 1 km (20 - 10 = 10°C). Then it cools at the wet adiabatic rate, about 6°C/km. At 3 km: 10°C - (2 km × 6°C/km) = -2°C. Reasoning: use the dry rate until the dew point is reached, then the wet rate after condensation begins.
Traps That Cost Marks
- Coriolis changes direction, not wind speed.
- High pressure means sinking air, not stormy weather.
- Greenhouse warming is not the same as ozone depletion.
- Hurricanes do not form at the equator because Coriolis is zero there.
- A cold snap does not disprove a long-term climate trend.