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Hi, I'm Atousa Saberi. I'm a
scientist and data visualizer at

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NASA Goddard, and I'm going to
be taking a deeper dive into the

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visualization of the weather
phenomenon known as El Nino and

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La Nina. This is a map of sea
surface temperature around the

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globe. As you can see, the ocean
temperature is not uniformly

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distributed. The equator
receives more solar radiation

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per unit area than the poles.
Therefore, the tropical oceans

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are warmer than the other parts
of the world. The surface water

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in the western Pacific, off the
coast of Asia are often warmer

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than the eastern Pacific. In
addition to solar radiation,

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winds, currents and clouds can
also change the temperature

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pattern. Let's isolate the
Pacific Ocean and look at the

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changes below the surface. At
the equator, below the surface,

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there is a sharp change in the
temperature that separates the

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warmer surface water from the
deep, cool water. This is known

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as the Thermocline, and is
typically identified by the

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depth of the 20 degrees
centigrade, or constant

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temperature, also known as the
20 degrees C isotherm. Typically

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in the east pacific the cold
water is close to the surface.

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And in the West, the accumulated
warm water pushes down the

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thermocline. Every two to seven
years, the warm pool of water

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spreads eastward into a long,
shallow pool, flattening the

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tilt of the thermocline. This
phenomenon is called El Nino. El

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Nino is one of the two phases of
the larger phenomenon called El

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Nino Southern Oscillation, or
ENSO. The other phase of ENSO is

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La Nina. El Nino is the warm
phase, and La Nina is the coal

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phase. From November 2021, to
December 2023, we had the unique

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opportunity to observe the
transition from La Nina to El

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Nino. ENSO has important
consequences for weather around

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the globe, such as changing
flood and drought patterns. To

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make the changes in the
temperature easier to see, let's

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show the temperature deviation
from normal conditions instead

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of the absolute temperature. One
indicator for El Nino is an

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index defined by sea surface
temperature deviation from

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normal in a particular region in
the Pacific. This region in the

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Central Pacific is called Nino
3.4 region. During La Nina, we

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see a cold tongue by the east
central Pacific. As El Nino

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develops in 2023 we see a warm
tongue extending across the

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Central Pacific. As we
transition from La Nina to El

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Nino, the Nino 3.4 index changes
from negative to positive

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values. We can also look at the
sea surface temperature, or SST

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on the globe, where the surface
water is exaggerated by the sea

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surface height deviation from
the normal condition. Colder

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SSTs produce dips, and warmer
SSTs create bulges in the sea

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surface. So during La Nina, the
sea level is generally lower

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than normal, and conversely,
higher than normal. During El

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Nino, these changes in the
surface temperature and the sea

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level are mostly driven by the
changes in the winds on the

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surface of the ocean. During La
Nina, the strong westward

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blowing trade winds push surface
waters to the west. As the trade

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winds weaken, the warm surface
water sloshes back to the

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Central Pacific, leading to a
central Pacific El Nino.

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In order to see these changes
better, let's look beneath the

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surface again. We highly
exaggerate the sea surface high

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changes to be able to see the
centimeters of changes across

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the Pacific. The subsurface also
shows warm anomalies in red,

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moving eastward as the surface
water moves away from the

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eastern Pacific, the cool deep
water moves upward along the

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coast of South America, we can
also see that the temperature

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anomalies move along the
thermocline as it's flattened by

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the El Nino development. The
temperature contrast across the

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Pacific is linked to the
atmospheric circulation right

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above the ocean, known as the
Walker circulation. The Walker

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circulation is driven by the
atmospheric convection over warm

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waters. The circulation spans
10,000 miles across the Pacific

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Ocean along the equator. It
extends vertically between the

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Earth's surface and the
tropopause, and horizontally

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from South America's western
coast to Australia and

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Indonesia. The Walker cell is
visualized with wind vector

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anomalies represented by
streamlines. The arrows are

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colored by the vertical
velocity. Upward is red and

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downward is blue. The bigger the
arrow heads, the stronger the

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winds upward or downward
velocities. During La Nina, the

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warm waters on the West Pacific
add extra heat to the air,

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resulting in rising motion where
there are more clouds and

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rainfall. Starting March 2023,
this cycle breaks down. The

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surface trade winds weaken the
warm water anomalies spread

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eastward, and therefore the
convective rising branch of the

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Walker circulation shifts to the
central and east pacific

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ENSO affects the global weather
by altering the rainfall

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pattern. During La Nina,
Indonesia and the maritime

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continent become wetter than
normal. During El Nino, it

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becomes drier than normal. In
the equatorial East Africa,

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conditions are drier than normal
during La Nina and wetter than

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normal during El Nino. In
northern Brazil, La Nina brings

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wetter than normal conditions,
while El Nino brings drier than

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normal conditions. The opposite
occurs in southern Brazil and

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Uruguay. Central America.
Northern Peru and Ecuador all

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experience heavy rainfall during
this El Nina. During La Nina,

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there is more upwelling of cold
water off the coast of Peru.

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Therefore, there is a higher
biological productivity, leading

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to a higher population of
zooplankton, which attracts fish

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schooling. This is reduced
during El Nino. Observing and

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studying these ENSO events can
be used as a source to make

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better predictions of the
climate system.