What do the “normal” trade winds do for the area?
In the Walker Cell they: push water westwards so that the level in the Philippines is normally 60sm higher than Panama and Columbia; allow water, flowing westward as the equatorial current, to remain near to the ocean surface where it can gradually heat (giving the world’s highest ocean temperatures - 28ºC). In contrast, as warm water is pushed away from South America it is replaced by an upwelling of colder, nutrient-rich water. Although this water lowers temperatures below 20ºC, it does provide a plentiful supply of plankton, which forms the basis of Peru’s fishing industry.
What changes in an El Nino Year?
The whole system relaxes.
What effect does an El Nino event have on the global climatic pattern?
El Nino has a major effect on places far beyond the Pacific margins as well as on those bordering the ocean itself in its low latitudes. This is because the upper air disturbances distort the path of the jet streams, which can lead to teleconnections all around the world. Between 1997 and 1998 the largest El Nino event occurred.
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Severe droughts were experienced in the Sahel and southern Africa as well as across the Indian subcontinent
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There were extremely cold winters in central North America
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Stormy conditions with floods in California
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Exceptional wet, milt and windy winters were experienced in Britain and north-west Europe
- In Peru for 12 days in early March, Peru received the equivalent of six months of normal rain. Over several months, flash flooding caused 292 deaths, injured more than 16000 people, left 400 missing, destroyed 13200 houses, wrecked 250000km of roads, swept away bridges, damaged crops, and schools, and disrupted the lives of up to half a million Peruvian.
- In parts of Kenya over 1000mm of rain fell during six months (up to 50 times more than the average) at a time normally considered to be the “dry” season. Roads and the mainline railway were swept away, the latter causing the derailment of the Nairobi-Mombasa train. Later, more than 500 people died of Malaria as the receding floodwater created mosquito-spawning pools.
Consider three climatic regions, how would El Nino affect each of these systems?
Tropical maritime climate – e.g. India.
El Nino disrupts the normal monsoon climate bringing drought and very high temperatures to areas unexpectedly and torrential rainstorms, causing mudslides to other areas.
What is La Nina and how does it differ from El Nino?
La Nina has the reversed climatic conditions of El Nino. However when La NIna does occur it is usually just before or after El Nino, however its occurrence has been less frequent and therefore harder to predict. In a La Nina event, in contrast to the normal conditions in the Pacific Ocean the low pressure over the western Pacific becomes even lower and the high pressure over the eastern Pacific even higher. This means that rainfall increases over South-east Asia, there are drought conditions in South America and due to the increased difference in pressure between the two places, the trade winds strengthen. The stronger trade winds: push large amounts of water westwards, giving a higher sea-level in Indonesia and Philippines: and increases the equatorial under-current and significantly enhance the upwelling of cold water off the Peruvian coast.
What global consequences are experienced when La Nina occurs?
Globally La Niña in very general terms will mean that those parts of the world who normally experience dry weather will be drier and those with wet weather will be wetter. The Atlantic and Pacific hurricane activity will increase with La Niña and the effects of severe droughts are now being considered for those parts of the world who are already suffering.
Broadly speaking, the La Niña event could give drier conditions in Central East Africa, SW USA, Northern Mexico, South America etc. Wetter conditions could be experienced in North/North East Australia, South Africa (which may cause further floodings similar to that in Mozambique and other countries in the region), Southern Asia (during the monsoon) and the northern half of South America, Central America and the Hawaiian Islands.
Whilst historically these are the effects of a La Niña event, as we have seen with El Niño, nothing is certain and the global impact is still to be fully understood.
