El Niño: local phenomenon, global impact.

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  • Current sea surface temperatures around the globe. Source: NOAA.

    Latest sea surface temperature anomalies. Source: NOAA.

    The basic mechanisms and characteristics of an El Niño episode. Source: NOAA.

    Normal conditions in the Equatorial Pacific. Source: NOAA

  • El Niño: local phenomenon, global impact.
    15.05.2014 10:12

     

    It is looking increasingly likely that this year we will see the emergence of the phenomenon known as El Niño, which occurs in the tropical Pacific but has implications on the weather across the globe.


    El Niño is the anomalous warming of the sea surface of the eastern Pacific, and the counterpart of La Niña, during which the eastern Pacific cools as strong Trade Winds push warm waters to the western Pacific, notably the seas around Indonesia.

    Eventually that warmer water, having “piled up”, as it were, in the western Pacific has to run back eastwards, and that can happen when the North-easterly Trades weaken. This is what is happening now, and we are already seeing warmer waters pushing to the surface off Ecuador and Peru. Quite what causes the fluctuations in the Trade Winds is another question, and one to which there is not yet a clear-cut answer.
     
    The probability of the onset of El Niño is around 70 per cent this summer, and forecasters, with the guidance of all major global models, are confident on this occurrence – but less so on how long it may last. There are some hints already that it might not persist through the winter, or at least that it will be over before next summer.  

    The effects on weather in other parts of the world vary, and in some regions the influence is stronger than in others. For example, El Niño is known to instigate drought and forest fires in the Indonesian archipelago, but more rain in parts of South America, notably Peru, Ecuador and Argentina, and in the south-eastern USA. The Indian monsoon tends to deliver less rain than average, and northern Australia is generally drier than normal.

    This can have serious impacts on water supply and food production. Improving skills in long-term forecasts through prediction of El Niño and La Niña episodes can help mitigate the effects or provide opportunities for commodities traders.  

    For Europe the impact of El Niño is smaller, less predictable, less well defined and more variable. However, sometimes as El Niño begins there is a tendency for Europe to have greater chances of high pressure regimes, and thus drier and hotter conditions than normal for a period during the summer. There are tentative hints that these sorts of conditions might develop this year, but no more than that; and there is no guarantee on when or even if the UK will fall under that anticyclonic influence.

    By: Stephen Davenport