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Environment

Closing in on El Niņo

   
 
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The 97/98 El Niņo caused not only serious disastrous flooding in America, Africa and Asia, but also led to severe droughts and bush fires in Indonesia (our picture) and Brazil. All these climatic regional perturbations were in fact well predicted by the medium-term weather forecasting models of the European meteorologists involved in the PROVOST project..
In the winter of 1997/1998 the world experienced another El Niņo event, a disruption to global weather that occurs every few years. This El Niņo was notable for two reasons. First, it was the strongest this century and second, scientists accurately predicted its effects many months in advance. This was possible because of a highly sophisticated computer model developed with the help of EU-funding by a team involved in the PROVOST project. The model represents a marriage between a 10-day weather forecasting model developed by the European Centre for Medium-Range Weather Forecasts (ECMWF) and an ocean model developed by a German team of oceanographers.

 

Usually, water in the western Pacific Ocean is warm at the equator. As you move east towards the American continent, the ocean gets much colder because it is continually suffused by upwellings of deep, cool water. However, every two to seven years, the build-up of heat energy in the western ocean causes warm water to drift eastwards and strong westward-blowing trade winds to subside. This significant change in climate, which has been given the odd nickname of "El Niņo" (the "Little Boy") has serious consequences for many parts of the world. The 97/98 El Niņo caused disastrous flooding in Africa, in China, and all along the Pacific coast of the American continent. It also led to severe droughts and bush fires in Indonesia and Brazil. Europe escaped the more violent consequences of El Niņo, but we still saw some pretty unusual weather.

All of this was predicted by a team of scientists at ECMWF, the European Centre for Medium-Range Weather Forecasts based at Reading in the UK. The Centre is funded by the national weather services of 18 European countries. Meteorologists in Europe decided long ago to pool resources to improve short- and medium-term weather forecasting, sharing the very high cost of the necessary computer hardware. The EU-funded PROVOST project has been contributing to the work of the ECMWF since 1996.

Making forecasts possible
The task of developing a computer model capable of long-term forecasts began in earnest with TOGA. This major research programme was co-ordinated by the United Nations and ran from the mid-1980s until the mid-1990s. It was important for the further development that has taken place as part of PROVOST for three reasons.

  • It demonstrated that there was a scientific basis for seasonal forecasts that could predict the effects of an El Niņo event some months before they were felt.
  • It promoted acceptance that El Niņo has a global effect on the world's weather.
  • It set in place the TOGA-TAO array - a network of moored buoys in the ocean that constantly feed back information about the physical conditions in the Pacific Ocean. The temperature of the ocean is measured every day to a depth of 500m at each ATLAS buoy mooring in the TOGA-TAO observing array in the Pacific and transmitted via satellite for distribution on the Global Telecommunications System. In addition, wind velocity and humidity are measured and transmitted three times per day. Buoys remain in position for up to a year before being recovered and refurbished.

Scientists at ECMWF became convinced that better forecasts of the effects of El Niņo would be possible if they were to couple a weather prediction model to an ocean model. The Centre already had a fully operational atmospheric model that could make accurate 10-day global forecasts, but they had no ocean model for the Pacific. They knew that a team at the Max-Planck Institute for Meteorology in Hamburg had built the Hamburg Ocean Primitive Equation model (HOPE). This system had everything they needed and the two groups quickly established collaboration. Very shortly afterwards, a call was made for projects by the Environment and Climate programme (within the EU's Fourth Framework Programme). A consortium coordinated by the ECMWF submitted a proposal for a research project based on this cooperation and including other European research groups working on the same subject, which was accepted for EU support. PROVOST (PRediction Of climate Variations On Seasonal Timescales) began in 1996.

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Predicting the effects of the 1997/98 El Niņo
The blue areas indicate areas of the world for which wetter weather than usual was forecast; the yellow/orange areas indicate forecasts of drier weather than usual. The deeper the colour, the more severe the effect. The floods in China and along the Pacific Coast from the US to South America, the very dry conditions in Indonesia and Brasil, as well as the warm winter over Europe were all clearly predicted.

A fully operational model
A version of the HOPE model was coupled to the ECMWF atmospheric model and, since then, much of the PROVOST project has been dedicated to testing the atmospheric component of the model using data available from previous El Niņo years. The raw data was fed into the model and the predictions that it made were compared to the actual global weather patterns that are a matter of record. "We call these tests hindcasts, rather than forecasts, and they are tremendously revealing," comments Tim Palmer. "We have had to make hundreds of runs to fine tune the model and to find out the limits of its accuracy but we are now running it in real time."

Two years into the project, things are going well. The model is fully developed and the recent strong El Niņo gave it the chance to impress. The predictions of world weather made last autumn have turned out to be very close to reality (see map). But, as Tim Palmer points out, "This is a good result, but it could be a mixed blessing. The ocean signals that allow us to predict the effects of are much easier to distinguish from the background 'noise' in the atmosphere when the El Niņo event is a strong one. In the future, the model will face the tougher test of weaker El Niņo events, and forecasts will not be as easy to make. We still have a lot of work to do."

 

 

Project Title:  
A European Programme on Prediction of Climate Variations on Seasonal and Interannual Timescales (PROVOST)

Programmes:
Environment and Climate (1994-1998)

Contract Reference: ENV4950109

CORDIS databaseFor more information on this project,
go to the Cordis database Record

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