AP Environmental Science 4.5: Global Circulation

Maximum 2 points: 1 point for correctly describing what the Coriolis effect is and 1 point for correctly

describing how it affects global atmospheric circulation patterns.

Radiation from the sun that reaches Earth is the primary factor that determines Earth's climate patterns,

which in turn is the primary factor that determines the location and types of biomes found on Earth. These

biomes range from extremely cold and dry polar regions to hot and humid tropical regions.

Due to more sunlight (measured in both duration and intensity) reaching the tropical areas (between

30°N and 30°S latitudes), in those regions air is able to hold more water vapor. As this moist air warms, it

becomes less dense and rises until it reaches the upper levels of the atmosphere, where it begins to cool.

This rising warm air also pushes the air mass away from the equatorial regions toward the polar regions. As

the air cools, the water vapor condenses, forming clouds that eventually will produce rain. These events

occur in atmospheric areas of Earth known as Hadley cells.

Starting at around 30°N and 30°S latitudes, this air begins to descend. As it descends, the air expands,

gets farther from the dew point (becomes drier), and draws moisture out of the soil, resulting in arid deserts.

If the Earth did not spin on its axis, this cycle of evaporation, condensation, and precipitation would

move air and its water vapor along a north-south axis from the equator to the poles, but this does not happen

due to the Coriolis effect. Due to the Earth's rotation, air returning to Earth's surface is deflected by the

Coriolis force, which shifts the flow of air to the right in the Northern Hemisphere and to the left in the

Southern Hemisphere. Winds blowing toward the equator are deflected to the west, creating the easterly

trade winds (easterly winds blow from east to west). In the temperate zones, where the winds blow toward

the poles, the Coriolis force deflects them toward the east, with prevailing westerlies (blowing from west to

east).

Maximum 4 points: 1 point for each arrow that is correctly placed into the diagram showing how the

Coriolis effect affects global wind patterns.

Maximum 1 point for correctly describing how global ocean surface current circulation patterns are

affected by global atmospheric patterns and the Coriolis effect.

Earth's rotation affects ocean currents in a manner similar to the way it affects atmospheric air currents.

Ocean currents are driven by surface winds, Earth's rotation, and differences in salinity.

Ocean surface waters near the equator flow from east to west, due in part to trade winds. And, as in the

atmosphere, the Coriolis force causes ocean currents to be deflected away from the equator (or northward

and clockwise in the Northern Hemisphere and southward and counterclockwise in the Southern

Hemisphere). As these waters approach their respective poles, the surface waters become colder and colder,

with some of the water freezing; however, during the freezing process, salt does not remain in the ice, but

rather remains in the ocean water, which ultimately results in a higher seawater salt content in the colder

water. With this higher ocean salinity and colder water temperature occurring near the poles, the surface

waters sink and set up a large "conveyor belt" of seawater that travels along the ocean floors, eventually

reaching the Atlantic Ocean.