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Major shifts in the weather patterns over the Indian and Pacific Oceans disrupt El Nino – University of Reading

The current El Nino is showing signs of weakening due to major shifts in weather patterns over the Indian and Pacific Oceans, scientists at the University of Reading's Walker Institute have discovered. Recent speculation has highlighted that the current El Nino – a dramatic warming of the tropical Pacific Ocean - is likely to persist and make 2007 the warmest year on record, but in the past two to three weeks, the El Nino has shown signs of weakening because of major shifts in weather patterns over the Indian and Pacific Oceans. Whilst much of the latter part of 2006 saw reduced rainfall over Indonesia, largely as a consequence of El Nino, the last two to three weeks have recorded several extreme rainfall events in Indonesia with flooding and loss of life as the weather patterns began to change. These major shifts in weather, seen in the sequence of satellite images shown below, are associated with an eastward propagating system known as the Madden Julian Oscillation (MJO), which typically takes 30-60 days to complete a circuit of the globe and leads to dramatic changes in local and regional weather – such as periods of heavy rainfall followed by dry conditions. Extreme events such as tropical cyclones are frequently linked to active phases of the MJO. The recent development and propagation of the MJO from the Indian Ocean out over the Pacific has had a substantial effect on El Nino. During the last 2-3 weeks, the El Nino has shown signs of weakening with the return of the easterly trade winds, triggered by the heavy rainfall over the Indian Ocean and Indonesian region. Prof. Julia Slingo, Director of the Walker Institute at the University of Reading and an expert in tropical climate, said: "The recent changes in tropical weather patterns are quite remarkable and we will need to follow them closely to see how they will affect the behaviour of El Nino in the coming weeks. "At the moment, in its passage over the Indian Ocean, the MJO is disrupting El Nino, but it is possible that when it moves out over the Pacific Ocean it may act to re-invigorate the El Nino. The MJO is also having a huge impact on regional weather and we can already see that much of the heavy rainfall that affected East Africa in December has largely ceased and the Indian Ocean region is free of cloud." Scientists now working for the Walker Institute have been studying the effects of the MJO on the initiation and evolution of El Nino for many years, and were one of the first groups to identify the fundamental role that the MJO played in the extreme nature of the 1997/98 El Nino. Understanding and predicting the MJO remains a huge challenge. Climate models have significant difficulties in capturing the MJO and its impacts on El Nino and global weather patterns. Professor Slingo said: "This has been recognised as one of the most pressing problems in climate prediction because our inability to capture its behaviour affects not only our forecasts for the coming year, but also our projections of future climate change. Possible increases in the activity of the MJO with global warming - and we think these have already been observed - could have far-reaching consequences for El Nino, for monsoon rains and for extreme events." ends Notes to editors: 1. This is a joint press release between the Walker Institute at the University of Reading and the National Centre for Atmospheric Science (NCAS). 2. For more information and to arrange interviews please contact: Kathy Maskell or Maria Noguer on 0118 3787380. Alternative number: 0118 378 8315. 3. The Walker Institute for Climate System Research at the University of Reading is concerned with understanding our climate, in order to deliver better knowledge of future climate and its impacts for the benefit of society. It is composed of groups from a number of departments across the University. See visit the Walker Institute website. 4. Tropical climate research at the Walker Institute is carried out as part of the National Centre for Atmospheric Science – Climate Programme visit www.ncas.nerc.ac.uk . The National Centre for Atmospheric Science - NCAS - carries out the UK's core academic atmospheric research programme, including climate variability and climate change. NCAS is funded by the Natural Environment Research Council. The NCAS-Climate programme addresses fundamental questions in understanding and forecasting climate variability and change and its impacts ncas-climate.nerc.ac.uk.