Add to table of contents: Tornado scalePg. 94 Air pressure & windPg. 95

Air Pressure(Atmospheric Pressure) The push of air molecules on a surface or object. Air with a high density has a greater air pressure and air with less density has a lesser air pressure. When air heats up it expands and has less air pressure and density. When air cools down, it contracts and has a greater density and air pressure.

IN GENERAL: Hot Air rises = low air pressure Cold Air sinks = high air pressure

WIND DEFINITION: Movement of air CAUSE: horizontal differences in air pressure. Air flows from areas of higher pressure to areas of lower pressure. The unequal heating of Earth’s surface generates pressure differences. Solar radiation is the ultimate energy source for most wind.

Highs and Lows Cyclones are centers of low pressure. Anticyclones are centers of high pressure.

LOCAL WINDS Land and Sea Breezes – The land surface is heated more intensely during the daylight hours than an adjacent body of water is heated. – As a result, the air above the land surface heats, expands, and rises, creating an area of lower pressure. At night the reverse takes place.

GLOBAL WINDS Air heats up at the equator and rises. It moves towards the poles and cools down and sinks. This creates convection currents that we call global winds.

Coriolis Effect The Coriolis effect describes how Earth’s rotation affects moving objects. In the Northern Hemisphere, all free-moving objects or fluids, including the wind, are deflected to the right of their path of motion. In the Southern Hemisphere, they are deflected to the left.