Wind and the Ocean

Wind Currents of air Develop when two adjacent bodies of air have different densities. Denser air sinks, pushing less dense air upward. Convection current is produced. Density of air is affected by temperature and water vapor. Water vapor in an air mass decreases its density because water vapor is about half as dense as air.

Air Pressure Force of the air mass on earth High pressure: dry, dense air Low pressure: moist, less dense air.

Ocean Wind Sea breeze: cooler, denser air above the ocean or lake sweeps over the shore as air warmed by the land rises. -beach areas are usually cooler in the summer than inland Land breeze: at night, breezes blow off land as the warmer air over the ocean rises. Ocean winds tend to keep nearby coastal lands relatively warm in the winter and cool in the summer.

Global Winds Heat is not distributed evenly on the earth. The equator receives about 60 times more sunlight than the poles. Hot (and usually humid) equatorial air masses are less dense Cold (and usually dry) polar air is more dense.

Global Winds cont. At the poles cold, dense air sinks then flows toward the equator. Polar air warms as it moves toward the equator, At the equator, hot, moist and less dense air rises and moves toward the poles. Equatorial air cools as it moves toward the poles. Convection cells are formed.

Earth’s Rotation and the Effect on Wind Rotates from west to east Spherical so therefore the equator rotates faster than the poles Cold air from the north pole can’t keep up with the land beneath it Polar easterlies: blowing from the northeast from poles to 60° N. Trade winds: blowing from the northeast from 30°N to equator. Prevailing westerlies: blowing from the southwest from 30°N to 60°N (dominant winds in US)

Global Wind Patterns

Winds cont. Doldrums: light shifty winds at the equator (named for lack of wind) Horse latitudes: light variable winds at 30°N

Winds and Surface Currents Winds can produce currents if they blow from the same direction for long periods. When wind pushes constantly on the ocean surface, water particles at the surface begin to move but not in the direction of the wind. The rotation of the earth causes water to form a current at a 90° angle to the wind (Ekman spiral). Currents will move right in the northern hemisphere and left in the southern hemisphere.

Gyres Circular current Formed by a combination of prevailing winds, the rotation of the Earth, and land masses that interfere with the movements of water currents. Due to the Coriolis Effect they rotate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. Important because they move the drifting plankton thousands of km across the ocean.

Main Ocean Gyres