Physical Geography 101


Wind is air motion with respect to Earth's surface.
Wind typically refers to horizontal air movement.
Updrafts and downdrafts: vertical air movement.
Wind is created by differences in pressure in different location: pressure gradient
Air moves from high pressure to low pressure.
It will continue to move until the pressures are equal.
The greater the pressure gradient: the greater the force of wind.

Causes of Unequal Pressure on the Earth's Surface

Pressures differences by uneven solar heating of surface.
Coastal areas: development of sea-breezes.

Daytime Onshore Breezes

Land is heated by sun, which heats air above surface.
Air becomes less dense and rises. Low pressure area is created.
Air over water stays cooler due to 4 thermal properties of water
Forms a high pressure area.
Air moves from high to low pressure, creating a cool onshore breeze.

Nighttime Offshore Breezes

At night, land cools more rapidly than ocean, thus creating high pressure over land.
Water retains its heat longer than land, keeps air above water warm, creating a low pressure.
Breeze moves offshore.

Wind Measurement

Two measurements are needed to characterize air movement.
1) Wind Direction
2) Wind Speed

Coriolis Effect

Apparent force which causes free moving objects to appear to be deflected from its path of motion.
Cause by Earth’s rotation
Northern Hemisphere - deflection to right
Southern Hemisphere - deflection to left

Low Pressure Centers

High Pressure Centers