El Nino

Major snowstorms have buried the mid-Atlantic states  (Delaware, Maryland, New Jersey, New York, Pennsylvania, Washington D.C.), California is uncharacteristically receiving heavy rain, Britain has been paralysed by sub-zero temperatures and Australia has seen not only some of its hottest weather, but also some of its wettest. What's going on?

Well, El Nino is mostly to blame. But what exactly is 'El Nino' (pronounced 'ell-nyeen-nyoh') and why is it always greeted with such alarm?

Meteorologists (scientists who study weather) say this year we are seeing a particularly strong El Nino and this is why we are seeing some fairly extreme weather patterns across both sides of the Pacific Ocean.

Wind generally blows westerly around the equator.

This is part of the trade winds, a sort of wind-driven motorway of the oceans. So called because the gusts would quickly blow the big sailing ships full of tea, spices and silk around the globe.

Normally, these winds blow across the Pacific from Central and South America, pooling an area of warmed sea on the eastern side of the Pacific near Asia & Australia.

Cool water upwelling (is brought up from deeper ocean areas) replaces the water blown from the east. The cooler water brings with it an abundance of sea life and nutrients.

The warm water heats the air, water vapour forms clouds which rain over South East Asia, leaving Latin America drier.

Top - normal weather pattern. Warm water pooled in east Pacific.

Bottom - El Nino. Warm backwash across Pacific.

However, with an El Nino pattern, the winds die down for some reason and there is a backwash of the warmer waters across the Pacific. No upwelling takes place so the fishing grounds are depleted.

The weather patterns are reversed with Asia and Australia falling into drought and Latin America experiencing floods. The clouds that now build-up over Latin America disrupts normal wind flows around the globe and chaotic weather follows.

Above: Red areas show warm backwash in El Nino conditions

Because El Nino is so devastating to people, trade and farming, there are early warning systems in place. Across the Pacific is a network of sensors on buoys that can take measurements of air and water temperature, ocean currents as well as wind speed and feed the results back to base via satellites.  El Nino can now be predicted in advance.

El nino disrupts weather patterns around the world and can be held responsible for lethal heatwaves in India and Texas, late monsoons, fires in the Indonesian rainforests, floods in Bangladesh and China, mudslides in California, drought in Australia and harvest failures in Africa. Bleaching of coral reefs, a dramatic rise in diseases such as cholera and malaria & dengue fever, Hurricane Mitch, ice storms in Central America.

El Nino has occurred for the past 15,000 years every 10 or so years. However, it now appears to have sped-up and there is now often only four years between each El Nino pattern of warming. In between, there are also periods of  'La Nina' which produces a cooling of the ocean.

Source: www.guardian.co.uk