fijitimes/story.aspx?id=293231 Extreme La Niña events that affect weather conditions on both sides of the Pacific will almost double in frequency as the climate warms, a new study shows. This increase is likely to drive a corresponding increase in devastating weather conditions including floods in the Asia Pacific region, more severe and frequent west Pacific cyclones, droughts in the southwestern United States, and hurricanes in the Atlantic. In Australia, La Niña is associated with flooding, and was linked to the Queensland floods in 2011 that left at least 38 people dead, affected about 70 towns, saw the evacuation of thousands of residents and hit the economy by about $30billion. The finding, by an international team including Australian researchers, was published yesterday in Nature Climate Change. Lead author Dr Wenju Cai, chief scientist at Australias CSIRO Oceans and Atmosphere Flagship, says their work shows La Niña events will occur every 13 years compared with a past frequency of one every 23 years. During typical La Niña events, the central-to-eastern equatorial Pacific is colder than normal, inhibiting formation of rain- producing clouds there, but enhancing atmospheric convection and rainfall in the western equatorial Pacific. An extreme La Niña is defined as a cooling in the central Pacific that is greater than 1.5 degrees Celsius cooler than normal average temperatures. This increase is driven by increased land warming relative to the ocean and an increased frequency of extreme El Niño events, Dr Cai says. Dr Cai says extreme La Niña events tend to occur after an extreme El Niño because the El Niño events counter-intuitively aid the cooling process in the central Pacific. In an El Niño event the heat in the upper ocean tends to release to the upper atmosphere the cooler water at the oceans sub surface is more easily brought to the surface and easier to generate cooling in the central Pacific. The work follows on from a study by the same team last year, also published in Nature Climate Change, which showed a doubling in super El Niño events. Wenju says this latest study begins to fill the gap in understanding what will happen to El Niños counterpart La Niña.
Posted on: Tue, 27 Jan 2015 21:47:20 +0000
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