Air Masses Affecting LA

Los Angeles is affected by the cooler air masses that come inland off the Pacific Ocean and the warmer air masses coming from the desert.  This often leads to an inversion layer.  The marine atmospheric boundary layer forms with the inversion in place.  The marine layer is a layer of cool, moist maritime air with the thickness of a few thousand feet immediately below a temperature inversion.  The inversion layer traps the carbon emissions from the city and this causes the smog that is often associated with Los Angeles.

(Source: http://www.theweatherprediction.com/weatherpapers/109/index.html)

Source: http://rst.gsfc.nasa.gov/Sect14

 Marine Layer at LAX

My personal photo taken October 23, 2011

In addition, Los Angels is affected by the seasonal Santa Ana winds that blow in the fall, winter, and spring, peaking in December.  The wind usually has its origin when cold air spills southward into the Great Basin, trapped between the Rockies to the east and the Sierras and Southern California coastal range to the west. This cold air mass is characterized by unusually high pressure near the land surface. Winds are driven into Southern California when the pressure of this interior air mass exceeds the pressure along the California coast.

(Source: http://meteora.ucsd.edu/cap/santa_ana.html)

Source: http://meteora.ucsd.edu/cap/santa_ana.html