Some notes on El Niņo

At the end of 1997 a strong El Niņo was in full swing. It created quite a hype in the press. Terms like "the mother of all El Niņo's", accompanied by all kinds of catastrophe scenario's, were used.

Here some facts on El Niņo are given, and an attempt is made to bring the hype around it back into proportion.

The 1997-1998 El Niņo is indeed a strong one. It is at least as strong as the last "big one" in 1982 - 1983. It developed quite rapidly in May 1997 and up to March 1998 the sea water temperatures in the equatoral East Pacific have been 4 - 5 degrees C above normal. At the end of the 1997 the sea water temperature anomalies over there were at their maximum.

The consequences which are felt in and around the Pacific:

Normally the West Pacific is moist. Warm air rises over there and decends in the East Pacific. Over the equator an Easterly wind blows. This is the so called Walker Cell circulation. During El Niņo this moist (and warm water) area moves to the middle of the Pacific. Indonesia, The Philipines and Eastern Australia (*) are (much) dryer than normal, while Equador and North Peru are much wetter than normal. During strong El Niņo's the Walker Cell circulation is shifted to quite an extent. In 1982-83 some area's in Peru received 3000 mm of rain vs. normally 50 mm! The water off the coast of Peru is normally quite cool (19 deg. C). This water is rich in nutrients - and thus fish; this is the basis for fisheries in Peru. Like in 1982-83 they suffered severely from the effects.

The weather in North America is also influenced. The polar jet stream over the North Pacific is deflected Northwards. As a result the Western part of North America experiences a mild winter. Another result of El Niņo was the extremely quiet 1997 hurricane season in the Atlantic and the Caribbean. Not a single hurricane in August, and only one significant one in September (Erica). Westerly winds aloft in the tropical Atlantic prevented the formation of hurricane's.

Also in other parts of the world the weather is influenced although the "El Niņo connection" is often much less clear:

Droughts in West Africa (Senegal), Eastern South Africa (Zimbabwe), Northern South America (NE Brazil). Floods in Mid- and East Africa (Somalia, Kenia; Mombasa: 1100 mm in october and the first half of November 1997. 8x normal!) In 1997 the West Coast of Mexico was hit by a few hurricane's inflicting quite some damage. Also a hurricane of the "supertaiphoon" catagory (Linda, 160 Kts along the eyewall) formed in the East Pacific. It should however be borne in mind that the course of a hurricane (and its possible place where it makes of landfall) is a matter of chance. In 1983 California was raked by rather unusual winter storms. This has happened this year as well. But: There have been years with strong El Niņo's in which this did not occur.

So: There are strong (local) effects. But one should be very wary to connect all kinds of extreme weather events with El Niņo. (And also the Greenhouse effect ...!) Nowadays much more extreme weather reports make it to the headlines than in the past.

E.g.: There is no appreciable connection with the severety of the winters in Europe, a weak connection with the monsoon over the Indian Subcontinent, no connection with the activity of mid latitude storms over the North Atlantic. And: Up to now no indications of a connection between El Niņo and the current global warming ("The greenhouse effect") have been found. More over, a recent publication at the KNMI site points in the direction that there is no correlation between the temperature on Earth and the activity of the El Niņo cycle.  

(*) In January 1998 torrential rains fell on NE Australia, so apparently the thesis that during an
El Niņo there is drought in this part of the world isn't correct in all cases.