What are El Nino and La Nina?

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Warmer or colder than average ocean temperatures in one part of the world can influence
weather around the globe. Watch this Ocean Today video to
see how this works.

During normal conditions in the Pacific ocean, trade winds blow west along
the equator, taking warm water from South America towards Asia. To replace that warm water, cold
water rises from the depths — a process called upwelling.
El Niño and La Niña are two opposing climate patterns that break these normal conditions.
Scientists call these phenomena the El Niño-Southern Oscillation (ENSO) cycle. El Niño and La
Niña can both have global
impacts on weather, wildfires,
ecosystems,
and economies.
Episodes of El Niño and La Niña typically last nine to 12 months, but can sometimes last for
years. El Niño and La Niña events occur every two to seven years, on average, but they don’t
occur on a regular schedule. Generally, El Niño occurs more frequently than La Niña.

El Niño

During El Niño, trade winds weaken. Warm water is pushed back east, toward the west coast of the
Americas.

El Niño means Little Boy, or Christ Child in Spanish. South American fishermen first noticed
periods of unusually warm water in the Pacific Ocean in the 1600s. The full name they used was
El Niño de Navidad, because El Niño typically peaks around December.

El Niño can affect
our weather significantly. The warmer waters cause the Pacific jet stream to move south
of its neutral position. With this shift, areas in the northern U.S. and Canada are dryer and
warmer than usual. But in the U.S. Gulf Coast and Southeast, these periods are wetter than usual
and have increased flooding.

a graphic showing el nino weather pattern over nation

El Niño causes the Pacific jet stream to move south and spread further east. During winter, this leads to wetter conditions than usual in the Southern U.S. and warmer and drier conditions in the North.

El Niño also has a strong effect on marine life off the Pacific coast. During normal
conditions, upwelling brings water from the depths to the surface; this water is cold and nutrient
rich. During El Niño, upwelling weakens or stops altogether. Without the nutrients from the deep,
there are fewer
phytoplankton off the coast. This affects fish that eat phytoplankton and, in turn, affects
everything that eats fish. The warmer waters can also bring tropical species, like yellowtail and
albacore tuna, into areas that are normally too cold.

La Niña

La Niña means Little Girl in Spanish. La Niña is also sometimes called El Viejo, anti-El Niño, or
simply “a cold event.” La Niña has the opposite effect of El Niño. During La Niña
events, trade winds are even stronger than usual, pushing more warm water toward Asia. Off the
west coast of the Americas, upwelling increases, bringing cold, nutrient-rich water to the
surface.

These cold waters in the Pacific push the jet stream northward. This tends to lead to drought in
the southern U.S. and heavy rains and flooding in the Pacific Northwest and Canada. During a La
Niña year, winter temperatures are warmer than normal in the South and cooler than normal in the
North. La Niña can also lead to a more
severe hurricane season.

a graphic showing la Nina weather pattern over nation

La Niña causes the jet stream to move northward and to weaken over the eastern Pacific. During La Niña winters, the South sees warmer and drier conditions than usual. The North and Canada tend to be wetter and colder.

During La Niña, waters off the Pacific coast are colder and contain more nutrients than usual.
This environment supports more marine life and attracts more cold-water species, like squid and
salmon, to places like the California coast.

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