Complete Transcript

Complete Transcript

Narration: Kathleen Gaeta Greer

Transcript:

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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.