Hi, I'm Atousa Saberi. I'm a scientist and data visualizer at
NASA Goddard, and I'm going to be taking a deeper dive into the
visualization of the weather phenomenon known as El Nino and
La Nina. This is a map of sea surface temperature around the
globe. As you can see, the ocean temperature is not uniformly
distributed. The equator receives more solar radiation
per unit area than the poles. Therefore, the tropical oceans
are warmer than the other parts of the world. The surface water
in the western Pacific, off the coast of Asia are often warmer
than the eastern Pacific. In addition to solar radiation,
winds, currents and clouds can also change the temperature
pattern. Let's isolate the Pacific Ocean and look at the
changes below the surface. At the equator, below the surface,
there is a sharp change in the temperature that separates the
warmer surface water from the deep, cool water. This is known
as the Thermocline, and is typically identified by the
depth of the 20 degrees centigrade, or constant
temperature, also known as the 20 degrees C isotherm. Typically
in the east pacific the cold water is close to the surface.
And in the West, the accumulated warm water pushes down the
thermocline. Every two to seven years, the warm pool of water
spreads eastward into a long, shallow pool, flattening the
tilt of the thermocline. This phenomenon is called El Nino. El
Nino is one of the two phases of the larger phenomenon called El
Nino Southern Oscillation, or ENSO. The other phase of ENSO is
La Nina. El Nino is the warm phase, and La Nina is the coal
phase. From November 2021, to December 2023, we had the unique
opportunity to observe the transition from La Nina to El
Nino. ENSO has important consequences for weather around
the globe, such as changing flood and drought patterns. To
make the changes in the temperature easier to see, let's
show the temperature deviation from normal conditions instead
of the absolute temperature. One indicator for El Nino is an
index defined by sea surface temperature deviation from
normal in a particular region in the Pacific. This region in the
Central Pacific is called Nino 3.4 region. During La Nina. we
see a cold tongue by the east central Pacific. As El Nino
develops in 2023 we see a warm tongue extending across the
Central Pacific. As we transition from La Nina to El
Nino, the Nino 3.4 index changes from negative to positive
values. We can also look at the sea surface temperature, or SST
on the globe, where the surface water is exaggerated by the sea
surface height deviation from the normal condition. Colder
SSTs produce dips, and warmer SSTs create bulges in the sea
surface. So during La Nina, the sea level is generally lower
than normal, and conversely, higher than normal. During El
Nino, these changes in the surface temperature and the sea
level are mostly driven by the changes in the winds on the
surface of the ocean. During La Nina, the strong westward
blowing trade winds push surface waters to the west. As the trade
winds weaken, the warm surface water sloshes back to the
Central Pacific, leading to a central Pacific El Nino.
In order to see these changes better, let's look beneath the
surface again. We highly exaggerate the sea surface high
changes to be able to see the centimeters of changes across
the Pacific. The subsurface also shows warm anomalies in red,
moving eastward as the surface water moves away from the
eastern Pacific, the cool deep water moves upward along the
coast of South America, we can also see that the temperature
anomalies move along the thermocline as it's flattened by
the El Nino development. The temperature contrast across the
Pacific is linked to the atmospheric circulation right
above the ocean, known as the Walker circulation. The Walker
circulation is driven by the atmospheric convection over warm
waters. The circulation spans 10.000 miles across the Pacific
Ocean along the equator. It extends vertically between the
Earth's surface and the tropopause, and horizontally
from South America's western coast to Australia and
Indonesia. The Walker cell is visualized with wind vector
anomalies represented by streamlines. The arrows are
colored by the vertical velocity. Upward is red and
downward is blue. The bigger the arrow heads, the stronger the
winds upward or downward velocities. During La Nina, the
warm waters on the West Pacific add extra heat to the air,
resulting in rising motion where there are more clouds and
rainfall. Starting March 2023, this cycle breaks down. The
surface trade winds weaken the warm water anomalies spread
eastward, and therefore the convective rising branch of the
Walker circulation shifts to the central and east pacific
ENSO affects the global weather by altering the rainfall
pattern. During La Nina, Indonesia and the maritime
continent become wetter than normal. During El Nino, it
becomes drier than normal. In the equatorial East Africa,
conditions are drier than normal during La Nina and wetter than
normal during El Nino. In northern Brazil, La Nina brings
wetter than normal conditions, while El Nino brings drier than
normal conditions. The opposite occurs in southern Brazil and
Uruguay. Central America. Northern Peru and Ecuador all
experience heavy rainfall during this El Nina. During La Nina,
there is more upwelling of cold water off the coast of Peru.
Therefore, there is a higher biological productivity, leading
to a higher population of zooplankton, which attracts fish
schooling. This is reduced during El Nino. Observing and
studying these ENSO events can be used as a source to make
better predictions of the climate system.