Weather, Climate, and the Atmosphere
What to know
The atmosphere is layered: troposphere (weather, temperature decreases with altitude), stratosphere (ozone layer, temperature increases with altitude), mesosphere, thermosphere, and exosphere. Air pressure decreases with altitude. The atmosphere is about 78% nitrogen, 21% oxygen, with trace gases including carbon dioxide, water vapor, and argon.
Weather is short-term; climate is long-term average conditions. Uneven solar heating drives winds and currents. Warm air rises and expands, creating low pressure; cool air sinks, creating high pressure. Wind blows from high to low pressure. The Coriolis effect deflects winds and currents (right in the Northern Hemisphere, left in the Southern).
Clouds form when rising moist air cools to the dew point and condenses on particles. Precipitation types include rain, snow, sleet, and hail. Fronts: cold fronts bring rapid storms; warm fronts bring gradual precipitation. The water cycle - evaporation, condensation, precipitation, runoff, infiltration - moves water through the system. The greenhouse effect warms Earth as gases trap outgoing infrared radiation; human activity increases CO₂ and other greenhouse gases, driving climate change. El Niño and La Niña shift ocean and atmospheric patterns.
Traps
Questions confuse weather with climate, misplace the ozone layer (stratosphere, not troposphere), or say greenhouse gases "trap heat" as if they create energy rather than slowing its escape. Watch for winds described as blowing from low to high pressure.
Rule of thumb and worked example
A cold front occurs when cold, dense air pushes under warm, moist air, forcing rapid lifting; expect brief, intense precipitation and cooler temperatures afterward. A warm front brings gradual cloud cover and steady rain as warm air rides over cold air.