The Santa Ana winds are strong, extremely dry offshore winds that characteristically sweep through Southern California and northern Baja California in late fall and early winter. They can range from hot to cold, depending on the prevailing temperatures in the source regions, the Great Basin and upper Mojave Desert. The winds are known for the hot dry weather (often the hottest of the year) that they bring in the fall, and are infamous for fanning regional wildfires.
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The National Weather Service defines Santa Ana winds as
"Strong down slope winds that blow through the mountain passes in southern California. These winds, which can easily exceed 40 mph, are warm and dry and can severely exacerbate brush or forest fires, especially under drought conditions."[1]
It is often said that the air is heated and dried as it passes through the Mojave and Sonoran deserts, but according to meteorologists this is a popular misconception. The Santa Ana winds usually form during autumn and early spring when the surface air in the elevated regions of the Great Basin and Mojave Desert (the "high desert") becomes cool or even cold, although they may form at virtually any time of year. The air heats up due to adiabatic heating during its descent. While the air has already been dried by orographic lift before reaching the Great Basin as well as by subsidence from the upper atmosphere, the relative humidity of the air is further decreased as it descends from the high desert toward the coast, often falling below 10 percent.
The air from the high desert is initially relatively dense owing to its coolness and aridity, and thus tends to channel down the valleys and canyons in gusts which can attain hurricane force at times. As it descends, the air not only becomes drier, but also warms adiabatically by compression. The southern California coastal region gets some of its hottest weather of the year during autumn while Santa Ana winds are blowing. During Santa Ana conditions it is typically hotter along the coast than in the deserts.[2]
Note that while the Santa Ana Winds are an adiabatic wind, they are not a Föhn wind. A Föhn wind results from precipitation on the windward side of a mountain range which releases latent heat into the atmosphere which is then warmer on the leeward side (e.g. the Chinook or the original Föhn). The Santa Ana winds do not originate in precipitation, but in the bone-dry high deserts.
The combination of wind, heat, and dryness accompanying the Santa Ana winds turns the chaparral into explosive fuel feeding the infamous wildfires for which the region is known. Wildfires fanned by Santa Ana winds burned 721,791 acres (2,920.98 km2) in two weeks during October 2003.[3] These same winds have contributed to the fires that have burned some 426,000 acres (1,720 km2) as of late October 2007.[4]
Although the winds often have a destructive nature, they have some positive benefits as well. They cause cold water to rise from below the surface layer of the ocean, bringing with it many nutrients that ultimately benefit local fisheries. As the winds blow over the ocean, sea surface temperatures drop about 4°C (7°F), indicating the upwelling. Chlorophyll concentrations in the surface water go from negligible, in the absence of winds, to very active at more than 1.5 milligrams per cubic meter in the presence of the winds.
During the Santa Ana winds, large ocean waves can develop. These waves come from a northeasterly direction; toward the normally sheltered side of Catalina Island. Protected harbors such as Avalon and Two Harbors are normally protected and the waters within the harbors are very calm. In strong Santa Ana conditions, these harbors develop high surf and strong winds that can tear boats from their moorings and crash them onto the shore. During a Santa Ana, it is advised that boaters moor on the back side of the island to avoid the dangerous conditions of the front side.
A Santa Ana fog is a derivative phenomenon in which a ground fog settles in Southern California during the end of a Santa Ana wind episode. When Santa Ana conditions prevail, with winds in the lower two to three kilometers (1.25-1.8 miles) of the atmosphere from the north through east, the lower atmosphere continues to be dry. When the Santa Ana winds cease, the cool and moist marine layer forms rapidly. The air in the marine layer becomes very moist and fog occurs.[5][6]
A related phenomenon occurs when the Santa Ana condition is present but weak, allowing hot dry air to accumulate in the inland valleys that may not push all the way to sea level. Under these conditions auto commuters can drive from the San Fernando Valley where conditions are sunny and warm, over the low Santa Monica Mountains, to plunge into the cool cloudy air, low clouds, and fog characteristic of the marine air mass. This and the "Santa Ana fog" above constitute examples of an air inversion.
The similar winds in the Santa Barbara area occur most frequently in the late spring to early summer, and are strongest at sunset, or "sundown," hence their name, sundowner. Since high pressure areas usually migrate east, changing the pressure gradient in southern California to the northeast, it is common for "sundowner" wind events to precede Santa Ana events by a day or two.[7]
Winds blowing off the elevated glaciated plateaus of Greenland and Antarctica experience the most extreme form of katabatic wind, of which the Santa Ana is a type, for the most part. The winds start at a high elevation and flow outward and downslope, attaining hurricane gusts in valleys, along the shore, and even out to sea. Like the Santa Ana, these winds also heat up by compression and lose humidity, but since they start out so extraordinarily cold and dry and blow over snow and ice all the way to the sea, the perceived difference is negligible.
The winds are also associated with some of the area's largest and deadliest wildfires, including the state's largest fire on record, the Cedar Fire, as well as the Laguna Fire, Old Fire, Esperanza Fire, Santiago Canyon Fire of 1889 and the Witch Fire.
In October 2007 the winds fueled major wild fires and house burnings in Escondido, Malibu, Rainbow, San Marcos, Carlsbad, Rancho Bernardo, Poway, Ramona, and in the major cities of San Bernardino, San Diego and Los Angeles. The Santa Ana winds were also a factor in the November 2008 California wildfires.
In December 2011 the winds led to "state of emergency" declarations in several municipalities after 80+ mph gusts toppled hundreds of trees, power lines, and traffic signals throughout the San Gabriel Valley. Approximately 230,000 people were left without power for an extended period after the incident. [8]
The winds carry Coccidioides immitis and Coccidioides posadasii spores into nonendemic areas,[9][10] a pathogenic fungus that causes Coccidioidomycosis ("Valley Fever"). Symptomatic infection (40% of cases) usually presents as an influenza-like illness with fever, cough, headaches, rash, and myalgia (muscle pain).[10] Serious complications include severe pneumonia, lung nodules, and disseminated disease, where the fungus spreads throughout the body. The disseminated form of Coccidioidomycosis can devastate the body, causing skin ulcers, abscesses, bone lesions, severe joint pain, heart inflammation, urinary tract problems, meningitis, and often death.[11]
The United States government worked on a vaccine for Coccidioidomycosis during the mid-1960s, in the hopes of weaponizing C. immitis for use as an incapacitant. But the work was abandoned when medical epidemiology uncovered lethal effects on several segments of the population, and C. immitis was reclassified as a lethal agent.[12]
There is some belief the winds also create positive ions, which are believed to affect mood negatively. Many believe this to be the cause for the statistical increase in the number of suicides and homicides during these times. [13][14] [15] [16] [17]
According to the Los Angeles Almanac: "The original spelling of the name of the winds is unclear, not to mention the origin." The name "Santa Ana Winds" is said to be traced to Spanish California, when the winds were called devil winds due to their heat. Santa Ana winds may get their name from the Santa Ana Mountains in Orange County, the Santa Ana River or Santa Ana Canyon, along which the winds are particularly strong. The original form may have been an Anglicized version of the Spanish, Satana's winds, from the Spanish vientos de Satán ("winds of Satan"). Sanatanas is a rarer form of Satanas and is a translation of a native name in an unspecified language.
Dr. George Fischbeck was a widely viewed newscaster in Southern California in the 1970s and 1980s who helped to familiarize Californians with the winds, which he referred to by their other common name, the "Santana winds" (Santana is a Spanish contraction for Santa Ana), noting that they were not confined to Orange County (where Santa Ana is located), but occurred throughout Southern California. He delighted in the symbolism of the devil's breath playing havoc with Southern California.
A recent popular guide book Los Angeles A to Z (by Leonard & Dale Pitt), credits the Santa Ana Canyon in Orange County as the origin of the name Santa Ana winds.
One account places the origin of the term Santa Ana winds with an Associated Press correspondent stationed in Santa Ana who mistakenly began using Santa Ana winds instead of Santana winds in a 1901 dispatch.
| “ | There was a desert wind blowing that night. It was one of those hot dry Santa Anas that come down through the mountain passes and curl your hair and make your nerves jump and your skin itch. On nights like that every booze party ends in a fight. Meek little wives feel the edge of the carving knife and study their husbands' necks. Anything can happen. You can even get a full glass of beer at a cocktail lounge. | ” |
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—Raymond Chandler, "Red Wind" |
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