The Circulation of Air

in the Troposphere

Wind• Wind is the horizontal movement of air parallel to

Earth’s surface.• Caused by differences in AIR PRESSURE

Wind Speed• Air pressure gradient: the difference in air pressure

for a certain distance.

Wind Speed• Measured with an anemometer.• Measured in:– Miles per hour– Knots (nautical mph)

Wind Direction• Air moves from HIGH pressure to LOW pressure.

• Coriolis Effect can modify the pattern of movement.

• Wind direction is named for the direction that it is coming FROM.

Convection Cells• Cooler, denser air, SINKS towards Earth, causing

warmer, less dense air to RISE.

Convection Cells• Jet Streams: bands of easterly moving air at the

top of the troposphere.– Winds blow 200 mph or more– Help steer air masses

Even though the wind "tries" to flow from high pressure to low pressure, the turning of the Earth causes the air flow to turn to the right (in the Northern Hemisphere), so the jet stream flows around the air masses, rather than directly from one to the other.

Seasonal Shifting of Wind & Pressure Belts

• Vertical rays of the Sun shift north and south with the seasons.

• Can cause quite different weather conditions

Seasonal Shifting of Wind & Pressure Belts

• Monsoons: extreme weather changes caused by the shifting wind and pressure belts.

Summer: wet, low P belt that is normally over the equator moves north and brings large amounts of rain to much of SE Asia and India

Winter: dry, high P belt is over the land, bringing dry air central Asia to SE Asia.

Weather Movement in the Unites States

• Prevailing SOUTHWESTERLY winds

Formation of Surface Ocean Currents

• Surface ocean currents are caused by wind blowing over the oceans and transferring energy to the water.– Direction is affected by blocking by landmasses and

Coriolis Effect.– Can seasonally shift position with the seasons.