La Niña is characterized by unusually cold ocean temperatures in the
Equatorial Pacific, compared to El
Niño, which is characterized by unusually warm ocean temperatures in
the Equatorial Pacific.
Shown below is the Reynolds sea surface temperature in the
equatorial Pacific from Indonesia on the left to central America on the
right (20N - 20S, 100E - 60W).
La Nina (cold) conditions - view of Pacific water temperatures
El Nino Conditions
Normal Equatorial Pacific Ocean surface temperatures (December 1993) are
shown in the middle panel, including cool water, called the 'cold tongue',
in the Eastern Pacific (in blue, on the right of the plot) and warm water
in the Western Pacific (in red, on the left). Strong La Niña conditions
during December 1998 are shown in the top panel. The Eastern Pacific is
cooler than usual, and the cool water extends farther westward than is
usual (see the blue color extending further to the left). Strong El Niño
conditions, in December 1997, are shown on the bottom panel, with warm
water (red) extending all along the equator. El Niño and La Niña are
opposite phases of the El Niño-Southern Oscillation (ENSO) cycle, with La
Niña sometimes referred to as the cold phase of ENSO and El Niño as the
warm phase of ENSO.
Recent La Niña and El Niño events
Different La Niña and El Niño events vary in strength
Mean and anomalies of sea surface temperature from 1986 to present,
showing El Niño events 1986-1987, 1991-1992, 1993, 1994 and 1997 and La
Niña events in 1985 and 1995.
In the left hand panel, you see the sea surface temperature at the Equator
in the Pacific Ocean (Indonesia is towards the left, South America is
towards the right). Time is increasing downwards from 1986 at the top of
the plot, to the present, at the bottom of the plot. The first thing to
note is the blue "scallops" on the right of the plot, in the eastern
Pacific. These indicate the cool water typically observed in the Eastern
Pacific (called the "cold tongue"). Cold tongue temperatures vary
seasonally, being warmest in the northern hemisphere springtime and
coolest in the northern hemisphere fall. The red color on the left is the
warm pool of water typically observed in the western Pacific Ocean. El
Niño is an exaggeration of the usual seasonal cycle.
During the El Niño in 1986-1987, you can see the warm water (red)
penetrating eastward in the Spring of 1987. There is another El Niño in
1991-1992, and you can see the warm water penetrating towards the east in
the northern hemisphere spring of 1992. The 1997-1998 El Niño (at the
bottom) is unusually strong.
El Niño and La Niña years are easier to see in the anomalies on the right
hand panel. The anomalies show how much the sea surface temperature is
different from the usual value for each month. Water temperatures
significantly warmer than the norm are shown in red, and water
temperatures cooler than the norm are shown in blue. In the right-hand
plot of sea surface temperature anomalies, it is very easy to see El
Niño's, with water warmer than usual (red) in the eastern Pacific, during
in 1986-1987, 1991-1992, 1993, 1994 and 1997-1998. It is unusual for El
Niños to occur in such rapid succession, as was the case during 1990-1994.
Notice the very cool water (blue), in the Eastern Pacific, in 1988-1989,
and the somewhat less cool water in 1995. These are La Niña events, which
occur after some (but not all) El Niños. Typically, El Niño occurs more
frequently than La Niña.
La Niña impact on the global climate
Global climate La Niña impacts tend to be opposite those of El Niño
impacts. In the tropics, ocean temperature variations in La Niña tend to
be opposite those of El Niño.
At higher latitudes, El Niño and La Niña are among a number of factors
that influence climate. However, the impacts of El Niño and La Niña at
these latitudes are most clearly seen in wintertime.
The origin of the names, La Niña and El Niño
La Niña is sometimes referred to as El Viejo
El Niño was originally recognized by fisherman off the coast of South
America as the appearance of unusually warm water in the Pacific ocean,
occurring near the beginning of the year. El Niño means The Little Boy or
Christ child in Spanish. This name was used for the tendency of the
phenomenon to arrive around Christmas.
La Niña means The Little Girl. La Niña is sometimes called El Viejo,
anti-El Niño, or simply "a cold event" or "a cold episode".
Selected references and publications
Philander, S.G.H., 1990: El Niño, La Niña and the Southern
Oscillation. Academic Press, San Diego, CA, 289 pp.