Earth #4: Hadley Circulation, Coriolis Effect, Rain Shadow Effect

Toward Poles: Sun’s rays spread over larger area; take longer path through atmosphere Near Equator: Sun’s rays strike Earth perpendicularly; more energy per square meter (heats Earth’s surface most intensely) Note: If earth flat, no latitudinal temperature gradient b/c sun would hit all surfaces equally

Hadley Circulation: Pattern of warm air rising in tropics (equator) and descending as dry air near 30 N and S latitude • Sun’s heating causes uplift of hot, expanded air • This creates large band of low atmospheric pressure • Hot air cools as lifting and holds less moisture • Cool air condenses into cloud • Cloud rains at equator (tropical rain forest) • Subsidence of air (sinking/downward movement of air over wide area within high pressure area) creates large band of high atmospheric pressure • Clouds start moving outwards • Clouds lose moisture while raining • Clouds fall as cool, dry air Thus, precipitation high at equator and low at 30 N and 30 S

Coriolis Effect: Northern Hemisphere: Wind bends clockwise right Southern Hemisphere: Wind bends counter clockwise left

Rain Shadow Effect: Area downwind of mountain/mountain range where little/no rain falls (rain travels w/ wind direction) Tropical Zones (closer to equator): West of mountains Temperate Zones (farther from equator): East of mountains