The Santa Ana winds are strong, extremely dry down-slope winds that originate inland and .... 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 ...
Santa Ana winds
From Wikipedia, the free encyclopedia
The Santa Ana winds sweep down from the deserts and across coastal
southern California, pushing dust and smoke from wildfires far out over
the Pacific Ocean. Los Angeles is in the upper left of this image, and
San Diego is near the center.
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. The winds originate from cool, dry
high-pressure air masses in the
Great Basin.
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.
[1][2]
Description
Meteorology
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."
[3]
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.
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.
[4] Santa Ana winds originate from
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 and into the Southern California region.
[5]
Cool, dry air flows outward in a clockwise spiral from the high
pressure center. This cool, 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. 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.
These passes include the
Soledad Pass, the
Cajon Pass, and the
San Gorgonio Pass, each of which is well known for its connection to the Santa Ana winds.
[6] As the air is funneled into the mountain passes, its velocity increases dramatically, often to near-
gale force or above. At the same time, as the air descends from higher elevation to lower, it is heated
adiabatically, warming about 5 °F for each 1,000 feet it descends (10 °C for each 1,000 m).
[6] As it warms, its capacity to hold moisture increases, so its relative humidity decreases. 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.
[7]
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. 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.
[8]
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") is cool or even cold.
QuikSCAT image showing the speed of the Santa Ana winds (m/s).
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 cool, dry, and stable high-pressure airmasses in the
high deserts.
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
land breeze 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.
[7][9]
Regional Impacts
Santa Ana winds often bring the lowest
relative humidities
of the year to coastal Southern California. These low humidities,
combined with the warm, compressionally-heated airmass, 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
wildfires for which the region is known. Wildfires fanned by Santa Ana winds burned 721,791 acres (2,920.98 km
2) in two weeks during October 2003.
[10] These same winds have contributed to the
October 2007 California wildfires that burned over 500,000 acres (2,000 km
2).
[11]
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.
Related phenomena
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.
[12][13]
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.
Sundowner winds
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.
[14]
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.
Historical impact
![[icon]](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png) |
This section needs expansion. You can help by adding to it. (December 2011) |
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.
[15]
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-nineteenth century.
[1]
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.
[1]
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 early December 2011, the Santa Ana winds were the strongest yet
recorded. At atmospheric set-up occurred that allowed the towns of
Pasadena and Altadena in the San Gabriel Valley to get whipped by 110
MPH sustained winds and 170 MPH gusts (unconfirmed).
[16]
The winds toppled thousands of trees, knocking out power for over a
week. Schools were closed, and a "state of emergency" was declared. The
winds grounded planes at LAX, destroyed homes and were even strong
enough to snap a concrete stop light from its foundation.
[17]
The winds also ripped through Mammoth Mountain and parts of Utah.
Mammoth Mountain hold California highest wind gust of 175 MPH from that
night.
In May 2014, the Santa Ana winds initiated the
May 2014 San Diego County wildfires, approximately four months after the
Colby Fire in northern
Los Angeles County.
Health effects
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.
[18] Even without ironclad scientific proof, it is a well-accepted part of local lore.
[2]
The winds carry
Coccidioides immitis and
Coccidioides posadasii spores into nonendemic areas,
[19][20] 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).
[21]
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.
[22]
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.
[2][23][24][25][26][27]
Etymology
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.
[1][4] 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".
[citation needed]
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.
[4]
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."
[28]
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.
[1][2]
| “ |
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.
|
” |
| — Joan Didion, Slouching Towards Bethlehem. |
See also
References
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. The winds originate from cool, dry high-pressure air masses in the Great Basin. 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.[1][2]The Santa Ana winds sweep down from the deserts and across coastal southern California, pushing dust and smoke from wildfires far out over the Pacific Ocean. Los Angeles is in the upper left of this image, and San Diego is near the center.
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.[4] Santa Ana winds originate from 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 and into the Southern California region.[5] Cool, dry air flows outward in a clockwise spiral from the high pressure center. This cool, 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. 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.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.
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 cool, dry, and stable high-pressure airmasses in the high deserts.QuikSCAT image showing the speed of the Santa Ana winds (m/s).
![[icon]](https://en.wikipedia.org/wiki/File:Wiki_letter_w_cropped.svg){kind=small}
No comments:
Post a Comment