El Nino
What
Is El Nino?
How
warm Pacific Ocean temps can alter the weather where you live
By Tiffany Means
Often blamed for any and all
out-of-the-ordinary weather, El Niño is a naturally occurring climate event and
the warm phase of the El Niño-Southern Oscillation (ENSO) during which sea
surface temperatures in the eastern and equatorial Pacific Ocean are warmer
than average.
How much warmer? An increase of 0.5 C or
more in average sea surface temperatures lasting 3 months in a row suggests the
onset of an El Niño episode.
Meaning
of the Name
El Niño means "the boy," or
"male child," in Spanish and refers to Jesus, the Christ Child.
It comes from South American sailors, who
in the 1600s, observed the warming conditions off the Peruvian coast at
Christmastime and named them after the Christ Child.
Why
El Niño Happens
El Niño conditions are caused by a weakening
of the trade winds.
Under normal circumstances, the trades
drive surface waters towards the west; but when these die down, they allow the
warmer waters of the western Pacific to seep eastward toward the Americas.
Frequency,
Length, and Strength of Episodes
A major El Niño event generally occurs
every 3 to 7 years, and lasts for up to several months at a time.
If El Niño conditions will appear, these
should begin to form sometime in the late summer, between June and August.
Once they arrive, conditions typically
reach peak strength from December to April then, subside from May to July of
the following year.
Events are categorized as either neutral, weak,
moderate, or strong.
The strongest El Niño episodes occurred in
1997-1998 and 2015-2016. To date, the 1990-1995 episode is the longest-lasting
on record.
What
El Niño Means for Your Weather
We've mentioned that El Niño is an
ocean-atmosphere climate event, but how do warmer-than-average waters in the
far-off tropical Pacific Ocean affect weather?
Well, these warmer waters warm up the
atmosphere above it. This leads to more rising air and convection.
This excess heating intensifies the Hadley
circulation, which in turn, disrupts circulation patterns around the globe,
including things like the position of the jet stream.
In this way, El Niño triggers a departure
from our normal weather and rainfall patterns including:
Wetter-than-normal conditions along coastal
Ecuador, northwestern Peru, southern Brazil, central Argentina, and equatorial
eastern Africa (during the months of December, January, February); and over the
inter-mountainous U.S. and central Chile (June, July, August).
Drier-than-normal conditions over northern
South America, Central America, and southern Africa (December, January,
February); and over eastern Australia, Indonesia, and the Philippines (June,
July, August).
Warmer-than-normal conditions in southeast Asia,
southeast Africa, Japan, southern Alaska, and west/central Canada, SE Brazil,
and SE Australia (December, January, February); and along South America's west
coast, and again SE Brazil (June, July, August).
Cooler-than-normal conditions along the U.S. Gulf coast (December, January, February).
Tiffany
Means
Meteorology
Expert
Education
B.S.,
Atmospheric Sciences and Meteorology, University of North Carolina
Introduction
Studied
atmospheric sciences and meteorology at the University of North Carolina
Former
administrative assistant for the National Oceanic and Atmospheric
Administration
Member
of the American Meteorological Society
Experience
Tiffany
Means is a former writer for ThoughtCo who contributed articles about weather
for five years. She has interned with the domestic and international weather
departments at CNN, written monthly climate reports for NOAA’s National Centers
for Environmental Prediction, and participated in a number of science outreach
events, including the Science Olympiad Competition. Means has personally
experienced such weather greats as the Blizzard of 1993 and the floods of
Hurricane Francis (2004) and Ivan (2004).
Education
Bachelor's
degree in atmospheric sciences and meteorology from the University of North
Carolina at Asheville
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