Editing Santa Ana winds (section)

== Description ==

=== Meteorology ===
The Santa Anas are [[katabatic wind]]s (Greek for "flowing downhill") arising in higher altitudes and blowing down towards sea level.<ref name="UCLA explains"/> The [[National Weather Service]] defines Santa Ana winds as "a weather condition [in southern California] in which strong, hot, dust-bearing winds descend to the Pacific Coast around Los Angeles from inland desert regions".<ref>{{cite web|title=Santa Ana Wind|url=https://w1.weather.gov/glossary/index.php?word=Santa+Ana+Wind|work=NOAA's National Weather Service Glossary|publisher=NOAA National Weather Service|access-date=25 January 2023}}</ref>

[[File:Santa ana winds.jpg|thumb|This map illustration shows a characteristic [[high-pressure area]] centered over the [[Great Basin]], with the clockwise [[anticyclone]] wind flow out of the high-pressure center giving rise to a Santa Ana wind event as the airmass flows through the passes and canyons of Southern California, manifesting as a dry northeasterly wind.]]

Santa Ana winds originate from [[high-pressure area|high-pressure]] airmasses over the [[Great Basin]] and upper [[Mojave Desert]]. Any [[low-pressure area]] over the Pacific Ocean, off the coast of California, can change the stability of the Great Basin High, causing a [[pressure gradient]] that turns the [[synoptic scale]] winds southward down the eastern side of the [[Sierra Nevada (U.S.)|Sierra Nevada]] and into the Southern California region.<ref name="UCSD CNAP">{{cite web|url=http://cnap.ucsd.edu/santa_ana.html|title=Santa Ana|date=October 3, 2015|website=cnap.ucsd.edu|publisher=California Nevada Applications Program / California Climate Change Center|access-date=October 30, 2015|url-status=dead|archive-url=https://web.archive.org/web/20151025155209/http://cnap.ucsd.edu/santa_ana.html|archive-date=October 25, 2015}}</ref> According to one meteorology journal, "a popular rule of thumb used by forecasters is to measure the difference in pressure between the [[Los Angeles International Airport]] and [[Las Vegas]]; a difference of 9 [[millibars]] (0.27 [[inches of mercury]]) is enough to support a Santa Ana event."<ref name="Vasquez2008" /> Dry air flows outward in a clockwise spiral from the high pressure center. This dry airmass sweeps across the deserts of eastern California toward the coast, and encounters the towering [[Transverse Ranges]], which separate coastal Southern California from the deserts.<ref>{{Cite news |last=Duginski |first=Paul |date=2022-03-12 |title=Why it's been so warm and windy in Southern California this winter |url=https://www.latimes.com/california/story/2022-03-12/why-its-been-so-warm-and-windy-in-southern-california-this-winter |access-date=2022-05-10 |newspaper=Los Angeles Times |language=en-US}}</ref> The airmass, flowing from high pressure in the Great Basin to a low pressure center off the coast, takes the path of least resistance by channeling through the mountain passes to the lower coastal elevations, as the low pressure area off the coast pulls the airmass offshore.<ref>{{Cite news|url=https://www.latimes.com/california/story/2019-10-25/two-destructive-fires-hundreds-of-miles-apart-one-culprit-winds|title=Two destructive fires. Hundreds of miles apart. One culprit: Winds|last1=Lin II|first1=Rong-Gong|last2=Duginski|first2=Paul|date=2019-10-25|newspaper=[[Los Angeles Times]]|language=en-US|access-date=2019-10-25}}</ref> 

Mountain passes which channel these winds include the [[Soledad Pass]], the [[Cajon Pass]], and the [[San Gorgonio Pass]], all well known for increasing Santa Anas as they are funneled through.<ref name="Vasquez2008" />  This increase in speed, often to near-[[gale force]] or above is due to the [[Venturi effect]] of the passes. At the same time, as the air descends from higher elevation to lower, the temperature and barometric pressure increase [[Lapse rate#Dry adiabatic lapse rate|adiabatically]], warming about 5&nbsp;°F for each 1,000&nbsp;feet it descends (1&nbsp;°C for each 100&nbsp;m).<ref name="LA Almanac">{{cite web |title=What are the Santana or Santa Ana Winds? |url=http://www.laalmanac.com/weather/we23.htm |url-status=live |archive-url=https://web.archive.org/web/20151102021007/http://www.laalmanac.com/weather/we23.htm |archive-date=November 2, 2015 |access-date=October 30, 2015 |work=Los Angeles Almanac}}</ref> Relative humidity decreases with the increasing temperature. The air has already been dried by [[orographic lift]] before reaching the Great Basin, as well as by subsidence from the upper atmosphere, so this additional warming often causes relative humidity to fall below 10 percent.<ref name="UCLA 2014">{{cite web|title=The Santa Ana Winds|url=http://www.atmos.ucla.edu/~fovell/ASother/mm5/SantaAna/winds.html|author=Fovell|publisher=[[UCLA]]|access-date=22 November 2015|url-status=live|archive-url=https://web.archive.org/web/20140201065518/http://www.atmos.ucla.edu/~fovell/ASother/mm5/SantaAna/winds.html|archive-date=1 February 2014}}</ref> 

The end result is a strong, warm, and very dry wind blowing out of the bottom of mountain passes into the valleys and coastal plain. These warm, dry winds, which can easily exceed {{convert|40|mph|km/h}}, can severely exacerbate brush or forest fires, especially under drought conditions.

During Santa Ana conditions it is typically hotter along the coast than in the deserts,<ref>{{cite web|title=Santa Ana Winds - Wildfires|url=http://www.noaawatch.gov/2008/santa_ana.php|work=NOAA Watch All Hazards Monitor|publisher=NOAA National Weather Service|access-date=10 February 2011|url-status=dead|archive-url=https://web.archive.org/web/20110310054135/http://www.noaawatch.gov/2008/santa_ana.php|archive-date=10 March 2011}}</ref> with the Southern California coastal region reaching some of its highest annual temperatures in autumn rather than summer. Frigid, dry arctic air from Canada tends to create the most intense Santa Ana winds.<ref>{{Cite news|url=https://www.latimes.com/california/story/2019-10-28/why-winds-this-week-may-be-the-strongest-of-the-season-thus-far|title=Why Santa Ana winds later this week may be the strongest of the season thus far|last=Duginski|first=Paul|date=2019-10-29|newspaper=[[Los Angeles Times]]|language=en-US|access-date=2019-10-29}}</ref>

[[File:SantaAnaWinds QuikSCAT 2002feb.jpg|thumb|left|[[QuikSCAT]] image showing the speed of the Santa Ana winds (m/s)]]
While the Santa Anas are katabatic, they are not [[Foehn wind|Föhn winds]]. These result 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 wind|Chinook]] or the original Föhn).

If the Santa Anas are strong, the usual day-time [[sea breeze]] may not arise, or develop weak later in the day because the strong offshore desert winds oppose the on-shore sea breeze. At night, the Santa Ana Winds merge with the [[Sea breeze#Land breezes|land breeze]] blowing from land to sea and strengthen because the inland desert cools more than the ocean due to differences in the [[heat capacity]] and because there is no competing sea breeze.{{r|UCLA 2014}}<ref>{{cite journal |last=Leneman |first=Mike |date=2015 |title=Devil winds: Santa Ana Winds explained by one of us |url=https://www.scribd.com/doc/288647313/The-Mariner-153 |journal=The Mariner |publisher=Pat Reynolds |volume=Nov 2015 |issue=153 |pages=8–9 |access-date=22 November 2015 |url-status=live |archive-url=https://web.archive.org/web/20151125072254/https://www.scribd.com/doc/288647313/The-Mariner-153 |archive-date=25 November 2015 }}</ref>

Santa Ana winds are associated in the public mind with dry hot weather, but cold Santa Anas not only exist but have a strong correlation with the highest "regionally averaged" wind speeds.<ref>{{Cite journal |last1=Gershunov |first1=Alexander |last2=Guzman Morales |first2=Janin |last3=Hatchett |first3=Benjamin |last4=Guirguis |first4=Kristen |last5=Aguilera |first5=Rosana |last6=Shulgina |first6=Tamara |last7=Abatzoglou |first7=John T. |last8=Cayan |first8=Daniel |last9=Pierce |first9=David |last10=Williams |first10=Park |last11=Small |first11=Ivory |last12=Clemesha |first12=Rachel |last13=Schwarz |first13=Lara |last14=Benmarhnia |first14=Tarik |last15=Tardy |first15=Alex |date=October 2021 |title=Hot and cold flavors of southern California's Santa Ana winds: their causes, trends, and links with wildfire |journal=Climate Dynamics |language=en |volume=57 |issue=7–8 |pages=2233–2248 |doi=10.1007/s00382-021-05802-z |issn=0930-7575 |pmc=8165508 |pmid=34092924|bibcode=2021ClDy...57.2233G }}</ref>

===Regional impacts===
[[File:Satellite image of Thomas Fire.jpg|thumb|The [[Thomas Fire]] and two other fires burn out of control near [[Ventura, California|Ventura]] in December 2017, with a strong Santa Ana wind driving the flames toward the coast and blowing the smoke offshore.]]
Santa Ana winds often bring the lowest [[relative humidity|relative humidities]] of the year to coastal Southern California. These low humidities, combined with the warm, compressionally-heated [[air mass]], plus the high wind speeds, create critical fire weather conditions. The combination of wind, heat, and dryness accompanying the Santa Ana winds turns the [[chaparral]] into explosive fuel feeding the infamous [[wildfire]]s for which the region is known. 

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 temperature]]s 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.<ref name="Vasquez2008" />

====Local maritime impacts====
During the Santa Ana winds, large ocean waves can develop. These waves come from a northeasterly direction toward the normally sheltered sides of the [[Channel Islands, California|Channel Islands]], including commonly visited [[Santa Catalina Island, California|Catalina]] and [[Santa Cruz Island|Santa Cruz]] islands. Normally well-sheltered harbors and anchorages such as [[Avalon, California|Avalon]] and [[Two Harbors, California|Two Harbors]] can develop high surf and strong winds that can tear boats from their moorings. During Santa Ana conditions, it is advised that boaters moor on the Southern side of affected islands or return to the mainland.<ref>Fagan, 2002, The Cruising Guide to Central and Southern California (International Marine)</ref>