El Niño's Last Hurrah?

El Niño 2009-2010 just keeps hanging in there. Recent sea-level height data from the NASA/European Ocean Surface Topography Mission/Jason-2 oceanography satellite show that a large-scale, sustained weakening of trade winds in the western and central equatorial Pacific during late-January through February has triggered yet another strong, eastward-moving wave of warm water, known as a Kelvin wave.
Now 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 150 degrees west and 100 degrees west longitude. A series of similar, weaker events that began in June 2009 initially triggered and has sustained the present El Niño condition.
JPL oceanographer Bill Patzert says it's too soon to know for sure, but he would not be surprised if this latest and largest Kelvin wave is the "last hurrah" for this long-lasting El Niño.
Patzert explained, "Since June 2009, this El Niño has waxed and waned, impacting many global weather events. I,and many other scientists, expect the current El Niño to leave the stage sometime soon. What comes next is not yet clear, but a return to El Niño's dry sibling, La Niña, is certainly a possibility, though by no means a certainty. We'll be monitoring conditions closely over the coming weeks and months."
An El Niño also causes unusual changes in atmospheric circulation and convection around the globe. JPL's Microwave Limb Sounder instrument on NASA's Aura spacecraft captured a large eastward shift of deep convection from the current El Niño, indicated by large amounts of cloud ice in the upper troposphere.
For more information, visit: http://photojournal.jpl.nasa.gov/catalog/?IDNumber=pia12961

Floundering El Ninos Make For Fickle Forecasts

Since May 2009, the tropical Pacific Ocean has switched from a cool pattern of ocean circulation known as La Niña to her warmer sibling, El Niño. This cyclical warming of the ocean waters in the central and eastern tropical Pacific generally occurs every three to seven years, and is linked with changes in the strength of the trade winds. El Niño can affect weather worldwide, including the Atlantic hurricane season, Asian monsoon season and northern hemisphere winter storm season. But while scientists agree that El Niño is back, there's less consensus about its future strength

One of the characteristics that signal a developing El Niño is a change in average sea surface height compared to normal sea level. The NASA/French Space Agency Jason-1 and Ocean Surface Topography Mission/Jason-2 satellites continuously observe these changes in average sea surface height, producing near-global maps of the ocean's surface topography every 10 days.
Recent data on sea-level height from the Jason-1 and Ocean Surface Topography Mission/Jason-2 satellites, displayed at http://sealevel.jpl.nasa.gov/science/jason1-quick-look/ , show that most of the equatorial Pacific is near normal (depicted in the images as green). The exceptions are the central and eastern equatorial Pacific, which are exhibiting areas of higher-than-normal sea surface heights (warmer-than-normal sea-surface temperatures) at 180 and 110 degrees west longitude.
The latest image from Jason-2, which can be seen at http://sealevel.jpl.nasa.gov/science/jason1-quick-look/2009/images/20090917P.jpg , reflects a 10-day data cycle centered around September 17, 2009. It shows a series of warm "bumps" visible along the equator, denoted in the image by a black line. Known as Kelvin waves, these pools of warm water were triggered when the normally westward-blowing trade winds weakened in late July and again in early September, sending them sliding eastward from the western Pacific toward the Americas. The Kelvin waves are 5 to 10 centimeters (2 to 4 inches) high, a few hundred kilometers wide and a few degrees warmer than surrounding waters. Traveling east at about 3 meters per second (6 miles per hour), they are expected to reach the coast of Peru in October. (An animation of the evolution of Pacific Ocean conditions since January 2006 is at: http://www.jpl.nasa.gov/videos/earth/elnino20090928.mov ).
Yet the present condition of this year's El Niño is dwarfed in comparison with the "macho" El Niño of 1997-1998, which brought devastating floods to California and severe drought to Indonesia, Australia and the Philippines. As seen in this September 20, 1997, image from the NASA/French Space Agency Topex/Poseidon satellite (see http://sealevel.jpl.nasa.gov/files/images/browse/entp2090.gif ), the size and intensity of the 1997-1998 event were much greater by this time of year. That leads some scientists, such as Bill Patzert, an oceanographer and climatologist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., to express uncertainty as to whether this El Niño event will intensify enough to deliver the dramatic impacts seen during that last intense El Niño in 1997-1998.
"For the past few months, the trade winds have weakened somewhat, but whether the new Kelvin waves traveling eastward across the Pacific will be adequate to pump this El Niño up enough to reinvigorate it and deliver any real impacts remains uncertain," Patzert says.
Patzert notes that it is important to remember that not all El Niños are created equal. "Some El Niños are show stoppers, but most are mild to modest, with minimal to mixed impacts," he says. He notes that since 1998, there have been three mild to moderate El Niño's: in 2002-2003, 2004-2005 and 2006-2007.
None of these events delivered the heart-thumping impacts of the monster El Niño of 1997-1998. During the winter of 1997-1998, Southern California was soaked with nearly 79 centimeters (more than 31 inches) of rain (twice Los Angeles' normal annual rainfall amount of about 38.5 centimeters, or 15.14 inches). In addition, there was heavy snowpack in the Sierra Nevada and Rocky Mountains. In comparison, during the past four winters, Los Angeles has averaged only 24.6 centimeters (9.7 inches) of rain (64 percent of normal), and snowpacks have been stingy.
In fact, Patzert notes that this El Niño bears many similarities to the 2006-2007 El Niño event. During that winter, much of the American Southwest experienced record-breaking drought, and Los Angeles had its driest winter in recorded history.
So what will El Niño 2009-2010 hold in store for the world this coming winter? In spite of the uncertainties, experienced climate forecasters around the world will continue to monitor the Pacific closely for further signs of El Niño development and will give it their best shot.
"Unless present El Niño conditions intensify, I believe this El Niño is too weak to have a major influence on many weather patterns," he says. "A macho El Niño like that of 1997-1998 is off the board, but I'm hoping for a relaxation in the tropical trade winds and a surprise strengthening of El Niño that could result in a shift in winter storm patterns over the United States. If the trade winds decrease, the ocean waters will continue to warm and spread eastward, strengthening the El Niño. That scenario could bring atmospheric patterns that will deliver much-needed rainfall to the southwestern United States this winter. If not, the dice seem to be loaded for below-normal snowpacks and another drier-than-normal winter."
Still, Patzert remains hopeful. "Don't give up on this El Niño," he added. "He might make a late break and put his spin on this fall and winter's weather systems."
To learn more about Jason-1 and the Ocean Surface Topography Mission/Jason-2, visit: http://sealevel.jpl.nasa.gov/ .
Adapted from materials provided by NASA/Jet Propulsion Laboratory.

El Niño, Global Warming Link Questioned; Possible Link Between 1918 El Niño And Flu Pandemic?

Research conducted at Texas A&M University casts doubts on the notion that El Niño has been getting stronger because of global warming and raises interesting questions about the relationship between El Niño and a severe flu pandemic 91 years ago. The findings are based on analysis of the 1918 El Niño, which the new research shows to be one of the strongest of the 20th century.

El Niño occurs when unusually warm surface waters form over vast stretches of the eastern Pacific Ocean and can affect weather systems worldwide. Using advanced computer models, Benjamin Giese, a professor of oceanography who specializes in ocean modeling, and his co-authors conducted a simulation of the global oceans for the first half of the 20th century and they find that, in contrast with prior descriptions, the 1918-19 El Niño was one of the strongest of the century.
Giese's work will be published in the current Bulletin of the American Meteorological Society, and the research project was funded by NOAA (National Oceanic and Atmospheric Administration) and the National Science Foundation.
Giese says there were few measurements of the tropical Pacific Ocean in 1918, the last year of World War I, and the few observations that are available from 1918 are mostly along the coast of South America. "But the model results show that the El Niño of 1918 was stronger in the central Pacific, with a weaker signature near the coast," Giese explains. "Thus the limited measurements likely missed detecting the 1918 El Niño."
Giese adds, "The most commonly used indicator of El Niño is the ocean temperature anomaly in the central Pacific Ocean. By that standard, the 1918-19 El Niño is as strong as the events in 1982-83 and 1997-98, considered to be two of the strongest events on record, causing some researchers to conclude that El Niño has been getting stronger because of global warming. Since the 1918-19 El Niño occurred before significant warming from greenhouse gasses, it makes it difficult to argue that El Niño s have been getting stronger."
The El Niño of 1918 coincided with one of the worst droughts in India, he adds. "It is well known that there is a connection between El Niño and the failure of the Indian monsoon, just as there is a well-established connection between El Niño and Atlantic hurricane intensity," Giese says. In addition to drought in India and Australia, 1918 was also a year in which there were few Atlantic hurricanes.
The research also raises questions about El Niño and mortality from the influenza pandemic of 1918. By mid-1918, a flu outbreak – which we now know was the H1N1 strain that is of great concern today – was sweeping the world, and the resulting fatalities were catastrophic: At least 25 million people died worldwide, with some estimates as high as 100 million deaths. India was particularly hard hit by the influenza.
"We know that there is a connection between El Niño and drought in India," Giese notes.
"It seems probable that mortality from influenza was high in India because of famine associated with drought, so it is likely that El Niño contributed to the high mortality from influenza in India."
The flu epidemic of 1918, commonly called the "Spanish Flu," is believed to be the greatest medical holocaust in history. It lasted from March of 1918 to June of 1920, and about 500 million people worldwide became infected, with the disease killing between 25 million to 100 million, most of them young adults. An estimated 17 million died in India, between 500,000 to 675,000 died in the U.S. and another 400,000 died in Japan.
Could the events of 1918 be a harbinger of what might occur in 2009?
Giese says there are some interesting parallels. The winter and spring in 1918 were unusually cold throughout North America, just at the time influenza started to spread in the central U.S. That was followed by a strengthening El Niño and subsequent drought in India. As the El Niño matured in the fall of 1918, the influenza became a pandemic.
With a moderate to strong El Niño now forming in the Pacific and the H1N1 flu strain apparently making a vigorous comeback, the concerns today are obvious, Giese adds.
Adapted from materials provided by Texas A&M University.

El Niño Affected By Global Warming

The climatic event El Niño, literally "the Baby Jesus", was given its name because it generally occurs at Christmas time along the Peruvian coasts। This expression of climatic variability, also called El Niño Southern Oscillation (ENSO), results from a series of interactions between the atmosphere and the tropical ocean. It induces drought in areas that normally receive abundant rain and, conversely, heavy rainfall and floods in usually arid desert zones.

Scientists term this phenomenon a "quasi-cyclic" variation because its periodicity, which varies from 2 to 7 years, shows no regular time pattern. Research conducted over the past 25 years, by oceanographers, climatologists and meteorologists has much improved knowledge on the mechanisms generating an El Niño event. However, possible influence of other systems of climate variability on the ENSO regime is more difficult to fathom. More particularly, it is not known if the intensity and frequency of the event is susceptible to modification in a situation of global warming.
The research work recently published by a team of Chilean and IRD scientists(1) sheds new light on El Niño's variability. Several geochemical factors contained in a drill core sediment sampled from 80 m depth under the Bay of Mejillones, in northern Chile, were determined. Analysis of breakdown byproducts from diatoms, unicellular planktonic algae, yielded an accurate trace of this region's trends in sea surface temperature between 1650 and 2000. Data for the period 1820-1878 showed a fall of over 2°C. This temperature decrease was also detected in two cores collected near the South-American coasts, over 1000 km to the North and South of Mejillones.
These samplings confirmed that the decrease in ocean temperature observed from 1820 affected the whole Pacific seaboard, from central Chile up to the North of Peru. All the oceanic area situated on the path of the Humboldt current system was therefore the scene of significant cooling during this period. This conclusion brings a paradox, seeing that the beginning of the XIXth Century coincided with the end of the Little Ice Age which came at the same time as a warming of the Earth.
Complementary analyses on certain minerals contained in the sediment samples confirmed that these minerals were transported by the winds from the continent. Therefore the reinforcement of such prevailing winds, the trade winds, would have favoured the rise of colder waters up from deeper reaches, along the Pacific coasts of South America, by pushing the ocean surface layer westwards. Confirmation of this hypothesis came from measurement of the organic carbon flux which is directly linked to growth in nutrient concentration. The increase in this flux accords with the phase of falling sea temperatures between 1820 and 1878 which proves that the rise in nutrient concentration stems from a rising up of cold water by the process of upwelling (2).
The hypothesis the researchers postulate suggests that, in a situation of climate warming like the one that followed the end of the Little Ice Age, the large continent--ocean temperature (and hence thermal) contrast would be responsible for this accentuation of the trade wind regime. Whereas the Atacama, a coastal-zone desert, warmed rapidly during this period, the sea surface temperature would have risen much more slowly. The long-term persistence of a substantial temperature difference between ocean and continent would have caused an intensification of the prevailing winds. Then by pushing the surface water towards the west, these winds would have induced cooling of the coastal waters, changing the normal feature of the El Niño regime which is a warming of the waters.
Between the end of the Little Ice Age and the beginning of the global warming attributable to human activities the ENSO regime was modified. Historical climatology studies founded on chroniclers' accounts and descriptions of floods caused by these El Niño events also showed an abrupt change, around 1820, in the ENSO system along Pacific seaboard of South America. Since the beginning of the XIXth Century, in other words the final phase of the Little Ice Age, the characteristic feature of El Niño events was abnormal rainfall, both in central Chile during the southern winter and on the northern coast of Peru during the subsequent southern summer.
These results as a whole emphasize the complexity of the interactions at work between the global-scale climate changes, the diverse behaviour of the ENSO system and regional climate changes. It remains to be determined if the extreme intensity of the two events which occurred at the end of the XXth Century, in 1982-1983, then in 1997-1998, is effectively linked to recent intensification of global warming. If that turned out to be the case, the El Niño phenomenon could become more and more intense and destructive, not only on the South American coasts, but also in other regions of the world.
Notes:
(1) This research was conducted jointly with the universities of Chile and Concepción (Chile). It follows-up work for a doctoral thesis by Gabriel Vargas presented at the University of Bordeaux I and financed by the IRD.
(2) This term designates the phenomenon of an uprising of cold water which occurs when the strong oceanic winds displace the sea surface waters.
Adapted from materials provided by Institut de Recherche Pour le Développement.