Ask an Expert

NASA Studies El Nino Using 30 Years of Earth Observations From Space
Satellite image showing the El Nino ocean warming effect in November 2009.

Sea-level height data from November 2009 shows that a large-scale, sustained weakening of trade winds in the western and central equatorial Pacific during October triggered a strong, eastward moving, wave of warm water, known as a Kelvin wave. In the central and eastern equatorial Pacific, this warm wave appears as the large area of higher-than-normal sea surface heights -- warmer-than-normal sea surface temperatures -- between 170 degrees east and 100 degrees west longitude. A series of similar, weaker events that began in June 2009 initially triggered and has since sustained the present El Niño condition. Image Credit: NASA/European Ocean Surface Topography Mission/Jason-2
› View large image
› NASA Fact Sheet: What is El Niño?

You may wonder how space and El Niño are related. NASA has invested substantial national resources in measuring key variables in our climate system, among them: temperature, water vapor, wind and radiative flux. These measurements are helping us understand how our climate system works. El Niño is the most prominent example of atmosphere and ocean coupling on our planet, involving wind stress driving ocean currents, sea-surface temperatures driving rainfall changes, and the heat liberated by the rainfall, in turn, driving the winds. It's one of Nature's never ending dances.

On Friday, Mar. 19, 2010, at 3 p.m. EDT, physical scientist Pete Robertson of NASA's Marshall Space Flight Center in Huntsville, Ala., answered your questions about El Niño and climate variability.

More About El Niño
There are frequently systematic changes in our weather patterns related to El Niño. In North America, El NiNiñoo creates warmer-than-average winters in the upper Midwest states and the Northwest, causing snowfall averages to drop in the winter. Meanwhile, central and southern California, northwest Mexico and the southwestern United States become significantly wetter while the northern Gulf of Mexico states and Southeast states, including Tidewater and northeast Mexico, are wetter and cooler than average during the El Niño phase of the oscillation. Summer is wetter in the intermountain regions of the United States. The Pacific Northwest states, on the other hand, tend to experience dry, mild but foggy winters and warm, sunny and early springs.

El Niño's warm current of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current. When El Niño conditions last for many months, extensive ocean warming occurs and its economic impact to local fishing for an international market can be serious.

The first signs of an El Niño are:
  • Rise in surface pressure over the Indian Ocean, Indonesia and Australia;
  • Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean;
  • Trade winds in the south Pacific weaken or head east;
  • Warm air rises near Peru, causing rain in the northern Peruvian deserts;
  • Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.
These patterns can also have an opposing phase know as "La Niña" -- our Earth's climate always wants to change!

Scientists at NASA are looking back at more than 30 years of data whereby much of our satellite measurements gathered to date are combined with computer models to derive the most consistent picture of climate and its variations during the era of Earth viewing satellites. These products, called re-analyses, give us the most accurate picture to date of El Niño and La Niña variations during this period.

Kim Newton, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.