Santa Ana winds
The Santa Ana winds are strong, extremely dry down-slope winds that originate inland and affect coastal Southern California and northern Baja California. Santa Ana winds blow mostly in autumn and winter, but can arise at other times of the year also. 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 especially for the hot dry weather (often the hottest of the year) that they bring in the fall, and are infamous for fanning regional wildfires. For these reasons, they are sometimes known as the "devil winds" across Southern California.
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 miles per hour (18 m/s), are warm and dry and can severely exacerbate brush or forest fires, especially under drought conditions."
Santa Ana airmasses originate from high-pressure systems over the Great Basin and upper Mojave Desert. The Santa Anas are a katabatic wind—katabatic meaning "to flow downhill" in Greek, which is an accurate description of the action of these winds. The air heats up from 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. 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).
As the cool, dense air from the desert blows out toward the coast, it tends to channel down the valleys and canyons and through the major mountain passes. Gusts can attain hurricane force at times. As it descends, the air not only becomes drier, but warms adiabatically from compression. The warm Santa Ana winds cause the Southern California coastal region to reach some of its annual high temperatures in autumn rather than summer. During Santa Ana conditions it is typically hotter along the coast than in the deserts.
Note that while the Santa Ana Winds are a katabatic 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. These same winds have contributed to the October 2007 California wildfires that burned over 500,000 acres (2,000 km2).
Although the winds often have a destructive nature, they have some 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.
Local maritime impacts
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 sheltered 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.
Santa Ana fog
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.
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. Because 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.
Arctic and Antarctic katabatic winds
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 because they start out so extraordinarily cold and dry and blow over snow and ice all the way to the sea, the perceived similarity is negligible.
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The Santa Ana winds and the accompanying raging wildfires have been a part of the ecosystem of the Los Angeles Basin for over 5,000 years, dating back to the earliest habitation of the region by the Tongva and Tataviam peoples.
The Santa Ana winds have been recognized and reported in English-language records as a weather phenomenon in Southern California since at least the mid-1800s. Various episodes of hot, dry winds have been described over this history as dust storms, hurricane-force winds, and violent north-easters, damaging houses and destroying fruit orchards. Newspaper archives have many photographs of regional damage dating back to the beginnings of news reporting in Los Angeles. When the Los Angeles Basin was primarily an agricultural region, the winds were feared particularly by farmers for their potential to destroy crops.
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 Creek 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.
Especially hot, dry, and dusty Santa Ana winds are widely believed (in Southern California, at least) to affect people's moods and behavior negatively. This has not been definitively proven in studies, although limited evidence may point to this conclusion. Even without ironclad scientific proof, it is a well-accepted part of local lore.
The winds carry Coccidioides immitis and Coccidioides posadasii spores into nonendemic areas, a pathogenic fungus that causes Coccidioidomycosis ("Valley Fever"). Symptomatic infection (40 percent of cases) usually presents as an influenza-like illness with fever, cough, headaches, rash, and myalgia (muscle pain). 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.
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.
The most well-accepted explanation for the name Santa Ana winds is that it is derived from the Santa Ana Canyon in Orange County, one of the many locations the winds blow intensely. Newspaper references to the name Santa Ana winds date as far back as 1886. By 1893, controversy had broken out over whether this name was a corruption of the Spanish term Santana (a running together of the words Santa Ana), or the different term Satanás, meaning satan. However, newspaper mention of the term "Satanás" in reference to the winds did not begin appearing until more than 60 years later. A possible explanation is that the Spanish language merges two identical vowels in elision. Thus the Spanish pronunciation of the phrase "Santa Ana" sounds like "Santana".
Another attempt at explanation of the name claims that it derives from a Native American term for "devil wind" that was altered by the Spanish into the form "Satanás" (meaning Satan), and then later corrupted into "Santa Ana." However, an authority on Native American language claims this term "Santana" never existed in that tongue.
A third explanation places the origin of the term Santa Ana winds with an Associated Press correspondent stationed in Santa Ana in 1902, who documented the name "Santa Ana winds," or possibly, mistook the term "Satana" for "Santa Ana." 
Santa Ana winds in popular culture
The Santa Ana winds are commonly portrayed in fiction as being responsible for a tense, uneasy, wrathful mood among Angelenos. Some of the more well-known literary references include the Philip Marlowe story "Red Wind" by Raymond Chandler, and Joan Didion's Slouching Towards Bethlehem.
|“||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.||”|
— Raymond Chandler, "Red Wind"
|“||The baby frets. The maid sulks. I rekindle a waning argument with the telephone company, then cut my losses and lie down, given over to whatever is in the air. To live with the Santa Ana is to accept, consciously or unconsciously, a deeply mechanistic view of human behavior.
...[T]he violence and the unpredictability of the Santa Ana affect the entire quality of life in Los Angeles, accentuate its impermanence, its unreliability. The wind shows us how close to the edge we are.
- Bora (wind)
- Chinook wind
- Climate of the Los Angeles Basin
- Diablo wind
- Norte (wind)
- Foehn wind
- Berg wind
- Katabatic wind
- Sundowner (wind)
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- Studying the Dust Kicked up by the Santa Anas
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- Lawrence L. Schmelzer, M.P.H.; Irving R. Tabershaw, M.D., F.A.P.H.A. (1968). Exposure Factors In Occupational Coccidioidomycosis. McGraw Hill. p. 110.
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- Los Angeles Times, Oct 25, 1964, Santa Ana winds that bleach and burn Southern California descend through ... ratio of positive ions to negative ions in the air is greater than normal.
- Los Angeles Times - Mar 12, 1988 "Negative ions make us feel good, positive ions make us feel badly," [Paul Blair ] said. Daily News of Los Angeles : SANTA ANAS: ILL WINDS THAT BLOW...
- The Gazette - Mar 30, 1999 The positive ions created by the winds may make people more irritable, anxious and aggressive. When Southern California's hot, dry Santa Ana winds blow into
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- What are the Santana or Santa Ana Winds?
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- University of California, San Diego, Meteorology Dept. Santa Anas (includes indicator if there are currently Santa Ana conditions)