2st PART









When this phenomenon occurs, many countries are affected.

Waters are less warm in Indonesia and anticyclones are created instead of the depressions. Which causes droughts in Australia and Indonesia, see also forest fires in areas that usually have abundant rainfall. But there are fewer hurricanes in the Western Pacific.

These waters which are brought across the Pacific cause a decrease of atmospheric pressure so an increase of precipitation on the East coast of South America (especially northern Brazil, the Peru) : see major flooding in usually desert areas.

In December 1997 and January 1998 during the "El Niño",
the Equator and North of the Peru received from 350
to 775 mm of rain and is 15 times more than normal.

Hurricanes affecting Polynesia are on the increase well as number tornadoes, causing dramatic consequences. The water it warms up it intersects upwelling (ascent) of cold water and nutrient-rich foods, and many kinds of fishes migrate towards the Pole, severely reducing the population in this part of the Pacific Ocean.

South and East Africa, South India, and Pakistan are also experiencing droughts and the floods in India are sporadic.

In the Atlantic ocean the number of hurricanes decreased during the El Niño phenomenon.

Click here to see the (SST) sea surface temperature anomalies
and the sea surface height (SSH) above animated.

El Niño from December to February

El Niño from June to August

Cool and rainy Warm and rainy
Warm and dry Cool and dry
Cool Dry
Rainy Warm

Click here to see an animation of the evolution of the snow cover from
August to July during El Niño years (1982/83, 1986/87 and 1991/92).
Red tones indicate less snow cover, blue tones indicate more snow cover.


During El Niño events, jet streams are intensifying because the rise in the
central Pacific temperature increases the pressure difference between the equator
and mid-latitudes. Then the jet streams determine the path of the mid-latitude storms.

Click here to see the effect of El Nino on the Jet Stream


As you can see, during the years of El Niño(highlighted in yellow) the
surface temperature of the water in the East Pacific along the equator is
higher than normal. The atmospheric pressure at Darwin and the records of
rainfall at Christmas Islands in the central Pacific are also higher than normal.


Click here to see the simulation of rainfall anomalies caused by
sea surface temperature observed from 1982 to 1998.

Click here for the forecast of El Niño or La Niña (source N.O.A.A.)


Since 2007 a new type of El Niño was found from the analysis of a Japanese group who named it warm pool El Niño or El Nino Modoki in Japanese. This El Niño is distinguished from its cousin by its specific impact on global atmospheric circulation..

Traditionally, the classic El Niño is associated with warming in the East tropical Pacific (Niño 1+2 et 3). However, during the El Niño Modoki sea surface temperature (SST) anomaly in East Pacific is not affected by a warming but rather by cooling just like the western equatorial Pacific, while a warm anomaly affects the central equatorial Pacific (Niño 3.4). These zonal gradients of SST translat into anomaly of two cells of the Walker Circulation on the tropical Pacific, with a humid region in the central Pacific. The thermocline doesn't tilt in the same way because during El Niño classic it rise up in West equatorial Pacific for descend in Eastern Pacific while during his cousin the thermocline rises at each end of the equatorial Pacific Ocean and sinks in the center of the Pacific.

Comparison during the situation of classic El Niño (a) and El Niño Modoki (b)

During classic El Niño West Coast of the United States is humid but during El Niño Modoki is rather dry. While during the classic El Niño there is a significant reduction of precipitation over the north and south of Australia, but Modoki event appears to result in a large-scale reduction in rainfall in the North West and Northern Australia. India is also affected by droughts with this second type of El Niño unlike classic phenomenon has long been known.


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