SoCal Santa Ana winds may be diminished by climate change

Articles — By forcechange on October 30, 2008 2:06 pm

Global weirding may be affecting a well known weather phenomenon experienced in Southern California.  Santa Anas, the hot easterly winds that whip down from the high desert areas into the coastal basins every Fall may actually be getting weaker as a result of climate change.

Researchers from UCLA believe that climate change may be diminishing a secondary force that is responsible for intensifying these winds.  Basically, Santa Anas are caused when a high pressure system sets up over the Great Basin (the high desert and mountain areas east of California).  This creates a pressure gradient between the two regions.  Since air naturally travels from high to low pressure area, this causes the traditionally west to east blowing winds to shift directions.  These easterly winds bring hot and dry air from the high deserts down into the coastal cities of SoCal, and are the primary cause of the catastrophic fires seen in the region each Fall.

However, there is also a magnifying effect on the Santa Anas that is called “temperature forcing,” which is being diminished as a result of overall temperature increases being seen in California’s climate resulting from global warming.  This magnifying effect is called “temperature forcing.” 

‘Temperature forcing’ plays a crucial role, and as the land warms more quickly than in the past, in the fall and early winter, this forcing loses some of its power. With a physics calculation, [UCLA researcher Alex] Hall’s team finds that this factor has fallen by about one-third, resulting in a slow but steady downtrend in the most dangerous winds.

According to Hall,

This is not a small effect.  It’s a well-known fact that the cool air that forms over the desert at night is part of the Santa Ana condition, and so, as the interior of California warms, the difference between the desert and the ocean air pressures is reduced. That’s why we’re seeing fewer Santa Ana conditions over Southern California, and why we should continue to see fewer until the warming of the ocean catches up to the warming of the land, which won’t be until sometime in the 22nd century.

This theory has not yet been published in a peer-reviewed journal, although Hall expects that to happen next year.