Learning Objectives   

Global wind patterns are the result of unequal heating of the Earth.  Global wind patterns are often modified by small scale or localized conditions.

Geostrophic winds imply no friction and generally include air movement above 1,000 meters.

The atmospheric boundary layer refers to air movement below 1,000 meters.  This air movement is affected by friction.  Surface features cause erratic movement and turbulence.  Thermal plumes from surface heating can also affect boundary layer winds.

The amount of turbulence encountered in the boundary layer is a function of:

• Surface heating: the greater the heating of the surface air, the greater the vertical movement of that air and the greater the resulting turbulence.
• Strong wind speeds: stronger winds enhance turbulence.
• Terrain: rough or hilly landscapes enhance turbulence.

Wind eddy: as air moves over an obstruction it will be diminished on the other side or move in a downward or opposite direction.  This has implications for airplanes.

Prevailing Wind: predominant direction from which the wind blows.

Sea Breezes: caused by differential heating between land and water on either a daily or seasonal basis.

Onshore Wind: wind blows from water to land.  Caused by air rising over warm land (daily heating) setting up circulation cell.

Offshore wind: wind blows from land to water.  Caused by air rising over warm ocean (land cools at night) setting up circulation cell.

Monsoon: Large scale sea breeze that occurs seasonally in areas where a large land mass is surrounded by water.
India is the classic example.

Mountain and Valley Breezes: movement of air around mountains and valleys caused by unequal heating between the night and the day.  Most pronounced in areas with exposed rock surfaces.

Upslope wind: wind moving upslope as it is warmed daily by heating.

Downslope wind: wind moves downslope due to cooling at night.

Katabatic Wind: very cold air flows down from an area of higher altitude.  Compressional heating occurs but the air is so cold it remains colder than the area into which it is blowing.

Chinook Wind:  wind at altitude encounters the Rocky Mountains (occurs with other mountains but called by other names).
As the wind moves over the mountains it is squeezed between the land surface and the bottom of the stratosphere.  As the air reaches the other side of the mountain it rushes downslope, is heated by compression, bringing warm temperatures.  Most pronounced when associated with a cyclone or anticyclone .

Santa Ana: a chinook wind that occurs when an anticyclone sits over the Basin and Range Province funneling air through the canyons and mountains of Southern California.  Often associated with wild fires.

Haboob: Strong up and down drafts associated with thunderstorm development in the desert.  No precipitation ever reaches the surface because it is too arid but dust and sand storms result from the up/down drafts.

Urban Heat Island Circulation: urban areas are warmer than the surrounding countryside.  Air rises over urban centers setting up a localized circulation cell.