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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
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› 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.

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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.


(Moderator) Jason: Hello everyone and welcome. Today we'll be talking about El Nino and its climate affects with Pete Robertson. Let's get started with this question -- Pete, what exactly is this thing called El Nino?

Pete: El Nino is a coupled instability between the ocean and the atmosphere centered in the equatorial Pacific. When trade winds weaken in the Pacific, warm water which had been piled up west of the dateline spreads eastward. The rain clouds which heat the atmosphere also move eastward. This causes a shift in wave patterns in the atmosphere and changes the way storm tracks propagate over the rest of the world.

(Moderator) Jason: To ask a question, please type out your question below and hit the "Ask" button on the right. This is a moderated chat. We're answering questions as soon as possible. Many thanks for your patience.

JohnE: How long is this El Nino predicted to last?

Pete: El Ninos typically peak in the winter season in the Northern hemisphere. We should expect to see it weaken this spring.

JohnE: Aren't El Ninos followed by La Ninas? If so, what will happen as a result of LaNina?

Pete: La Nina is like an opposite phase of El Nino when the trade winds strengthen, piling up warm ocean water in the far western Pacific. Droughts over the western US are statistically linked to these conditions. La Nina events can be more persistent and last several years. What is ENSO? ENSO stands for El Niño/ Southern Oscillation. The ENSO cycle refers to the coherent and sometimes very strong year-to-year variations in sea- surface temperatures, convective rainfall, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean during El Nino. El Niño and La Niña represent opposite extremes in the ENSO cycle. So, in La Nina conditions we can sometimes have a more active hurricane season in the Atlantic. We'll be watching to see if this La Nina develops, and if it develops rapidly...we may have an elevated hurricane season!

Kmulvey: Does El Nino affect fishing in the United States?

Pete: It does. Typically El Nino has effects that spread to middle latitudes, so we see fishing impacts in terms of fish populations in the Northern Pacific. It affects the fishing off the West Coast, and may bring in larger -- and different -- fish populations.

(Moderator) Jason: We've had some great questions so far. Submit yours and ask our expert. Please keep sending them in! Just type out your question below and hit the "Ask" button on the right.

Erikianlarsen: What kind of atmospheric ramifications does it have?

Pete: El Nino shifts the wave patterns in the atmosphere and has a large impact on storm tracks in the middle latitudes. So, the ones we see are typical of this past winter, with wet springs, dry and warm conditions in the Pacific Northwest. Like the Olympic Games -- they needed more snow that they got!

Ghoti: Are El Nino events occurring more frequently than 25 years ago?

Pete: It's hard to answer that in a statistically significant way. Had several very large ones, like 1998, and one in 1982-83 – and lots of little El Ninos. So 25 years isn't enough time to make an accurate assessment, but all are different and vary from decade to decade.

(Moderator) Jason: To ask a question, please type out your question below and hit the "Ask" button on the right. This is a moderated chat. We're answering questions as soon as possible. Many thanks for your patience.

Aenea01: Is 30 years long enough to really gain a comprehensive idea of the El Nino pattern and affects?

Pete: No, but the problem is, we only have really good observations during the past 30 years. Moored buoys, increased satellite observation capability (rainfall measurements, radiation from Earth, clouds and wind). We're learning more about El Nino processes. So we have to merge new information with older records of sea surface temperatures made from ships and surface pressure observations, and even tree ring records.

Caseface: Is El Nino the reason why we've had such a harsh winter?

Pete: Yes and no. Many of the strange things this winter (warm, dry weather for Pacific Northwest, storms in the southern U.S) are classic signatures of El Nino. But, some impacts seem to come from higher latitudes. Warming over northern Canada and Scandinavia may just be natural variability of weather or also be influences of El Nino.

DaveFlys: In what ways does El Nino affect the hurricane season in the United States?

Pete: Typically the summer of El Nino development will have weaker than normal hurricane activity. This is because El Nino weakens the vertical wind shear over the Atlantic. The opposite tends to happen during La Nina.

(Moderator) Jason: We've had some great questions so far. Please keep sending them in! Just type out your question below and hit the "Ask" button on the right.

Erikianlarsen: What are the long-term consequences of the dry, warm winter?

Pete: The Pacific Northwest’s exposure to drought has consequences for agriculture and for populations along the West Coast. So, prolonged drought in the Pac Northwest or the Western half of the U.S. can reduce river flow and holdings in reservoirs (Lake Meade), and also reduce drinking water supplies and availability for urban areas.

Erikianlarsen: What new advancements in technology is NASA using to track these types of events?

Pete: Monitoring the entire earth is a job that is uniquely suited to space. El Nino is our largest single planetary “climate fluctuation” -- it’s of global scale and consequence. NASA’s sensors used to study other planets are similar in many respects to those it uses to examine Earth. We measure rainfall and clouds and ocean surface topography with radars in space. NASA’s development of Earth sensors provides crucial data used by NOAA to help generate seasonal climate forecasts of El Nino conditions. We also have altimeters (Topex-Poseiden) and JASON, which measure surface topography.

Redreh: How much or how little has global warming contributed to El Nino, its appearances, and its effects?

Pete: Interesting question. There are competing theories here. One holds that because of upwelling cold water along the west coast of South America, most of the increase in ocean warmth will be concentrated in the western Pacific. This will make for stronger trade winds (because of the east-west gradient of sea-surface temperatures) and favor La Nina like conditions. On the other hand, in a warmer climate the amount of atmospheric circulation, or wind, needed to support convection will actually decrease. This would mean weakened trade winds and favor more El Nino like conditions. Currently, most model predictions favor the latter.

Graham: I work and live in Venezuela and we are having power restrictions due to low water levels in Lake Guri. What's the outlook for normal rain patterns in Venezuela and Colombia?

Pete: Well, in El Nino years we typically have reduced rainfall over the Amazon and Andes Mountain Range, so next year we expect things to be closer to normal.

Dataxy: When is an El Niño season is it the same time of the year? it seems to be at the last QT of the year?

Pete: El Nino events are "phase-locked" to the annual cycle because of the difference in the amount of land in the Northern and Southern Hemispheres, and they maximize in the December-January timeframe.

Swhite: The drought we had in far south Texas is over and we also have had nights with lows like 43 degrees every night which is cooler than normal even in most winter. I hope there is a low hurricane count because of the El Nino.

Pete: Let's hope so!

Rbranick: Are changes in atmospheric winds high enough in the atmosphere ( 20,000 to 50,000 feet) to change aircraft ground speeds substantially?

Pete: Since the changes in storm tracks occur in scale of days and weeks, then airlines can change routes to take advantage of or avoid high winds.

Dr._Joe_Resnick: Are there any secular changes in core samples of microbial communities that either document or explain/support the notion of 'global warming' or el Nino that demonstrate isotopic changes or changes in element cycling? Could you direct me to that data?

Pete: I'm not sure, but an interesting question!

(Moderator) Jason: Thanks for the good questions so far. To ask a question, please type out your question below and hit the "Ask" button on the right. This is a moderated chat. We're answering questions as soon as possible. Many thanks for your patience.

Daniel_Parra_Vento: What effect does El Nino have globally?

Pete: As we noted earlier, El Nino or opposite, La Nina, affects storm tracks in both hemispheres. So even sea surface temperatures in higher latitudes get modified and can propagate temps and rainfall patterns over land.

Poikiloblastic: How early can you confidently identify whether any given year will be an "El Nino year"?

Pete: We have a problem anticipating El Ninos from forecasts that begin earlier than May or June. That's because the initial phase of an El Nino may be sensitive to how strong the Asian monsoon develops. However, once we see warm water in the Western Pacific starting to move eastward, then our numerical models are reasonably good at forecasting the rest of the life of that event.

Bluezone: hi there!

Pete: Hi! Thanks for joining the chat. :)

Bluezone: Pete, is La Nina going to hit the hurricane season this year? When does La Nina play into effect? We're in Miami, Florida.

Pete: We talked briefly about La Nina before. We don't really know how soon the cold event (La Nina) will develop. We have the same problem anticipating the "birth" of these events, but we'll know something around early summer.

(Moderator) Jason: We've had some great questions so far. Please keep sending them in! Just type out your question below and hit the "Ask" button on the right.

Redreh: I've seen a lot of El Ninos in my short lifetime. It seems that they are on the increase. If this pattern continues, what will be the long-term effects on crops, livestock, and livelihoods? Is there anything we can do to counteract the effects?

Pete: Since the big El Nino in 1997-98, we've had several moderate El Ninos. Not knowing how old you are -- smile -- we've had various swings back and forth between weak and strong El Ninos. There's nothing we can do to directly affect El Nino. We're still unsure how El Nino statistics will change in the event of global warming.

Pete: By the way, this is a helpful link:

Redreh: Thanks! I'm 22, by the way, and El Nino just never seems to go away :)

Pete: Yes, that's true. Earth's tropical climate never reaches steady-state, and it prefers to flop back and forth between El Nino and La Nina-like conditions.

swimmo13: Do you think you will ever be able to accurately predict future El Nino years, or is it based solely on events that happen during each year?

Pete: Our prediction capability is steadily improving. in recent years, we've deployed more ocean buoys and we have better measurements of ocean circulation. So that should help us initiate our forecasts from a more accurate state. One big challenge is to improve the representation of deep rain clouds in our numerical models and their connection to evaporation over the ocean surface.

(Moderator) Jason: Just a reminder, this is a moderated chat. We're answering questions as soon as possible. Many thanks for your patience.

KIM: How did you get interested in working at NASA?

Pete: I was going to be a rocket scientist. Then, all the payloads I launched on my little rockets had parachutes on them, and they drifted away in the wind. So I got interested in meteorology and wind currents. I'm an engineer gone bad!

Pete: Also, before I forget, I wanted to mention that the Earth Systems Research Lab site is a great resource:

Also, for a look at rainfall anomalies from NASA's TRMM satellite, go to

Hello: Hello interesting to know this. Where do I get this information?

Pete: The links above are a good place to start. :)

(Moderator) Jason: We've had some great questions so far. Please keep sending them in! Just type out your question below and hit the "Ask" button on the right.

Hello: Hi Pete thx for that info.

Pete: My pleasure. :)

(Moderator) Jason: Thanks very much for all the great questions. We have time for just a few more before we end this chat. To ask your question, type it out in the box below and click on the 'Ask' button on the right.

KIM: Do you enjoy this type research and what kind of degree do you need to do this type work?

Pete: I'm lucky to have a job which is better than a hobby! I get to come to work and get my hands on some of the best observations of Planet Earth, courtesy of NASA and other international space agencies. My job involves satellite remote sensing, fluid dynamics, and math. So to prepare for a career in earth science, a good background in math, statistics, and physics is a great way to go.

Hello: Hi Pete, can we predict and divert the weather disaster?

Pete: No, we can't divert the weather, but we can plan for weather events, and minimize our exposure to extreme events. Our prediction capabilities are steadily improving.

KIM: Can you predict the next El Nino or El Nina? IF so, what would you tell affected regions to prepare for?

Pete: Well, we'll have to wait and see how our model predictions converge in the late spring. For example, will they all tend to indicate the beginning of a cold event (La Nina), starting this summer. If so, then we might take precautions regarding the possibility of additional tropical storms in the Atlantic.

swimmo13: Hi Pete, I saw a post earlier about why you got interested in working with NASA, but I'm wondering exactly how? I'm a sophomore chemical engineering major, and have always wanted to be an astronaut. What should I do or where should I go to look for internships involving aeronautics inside NASA?

Pete: is a great place to start.

(Moderator) Jason: Thanks very much for all the great questions. We have time for just a few more before we end this chat.

Hello: I hope we have that kind of technology so that we can save many such lives!

Pete: Better predictions will minimize economic losses. Life-threatening events are rarer in the U.S., but are still a problem in under-developed countries. Incidentally, with El Nino we typically expect warmer sea surface temperatures and a more intense wet season in the Caribbean. This could complicate relief efforts in Haiti, for example.

KIM: Was the severe hurricane season we had in 2005 related to El Nino?

Pete: It was partially related to El Nino, but we have to remember these relationships we've been talking about are statistical in nature, so we can't assign complete cause to any particular event.

Hello: I saw one post that is good place to start.. if possible can you please let us know which page to look for is it .... where do I find details about El Nino?

Pete: These are also good resources: Earth Systems Research Lab site at and for a look at rainfall anomalies from NASA's TRMM satellite, go to

Redreh: Thanks for this, it’s been great!

Pete: Thank you for your participation!

(Moderator) Jason: For more information about student internship and job opportunities, please see:

Hello: Quite interesting to know that NASA organizes such events so that people all around the world have access to chat...

Pete: Thanks! We like to communicate what we're working on and new understanding developed about Earth. NASA spends lots of resources looking outward from the planet, but we also have a long history of looking back at our home. We do it all. :) In fact, the first NASA weather-observing satellite was Tiros-1, launched. April 1, 1960.

(Moderator) Jason: Thanks to all of you for all the great questions, and thanks to our guest scientist, Pete Robertson! Our El Nino chat is now closed. Check back on Monday for a posted transcript of today’s chat. Have a great weekend.


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