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Wednesday, January 12, 2011

La Niña event likely to be strongest on record

The current La Niña weather pattern, part of the El Nino Southern Oscillation (El Nino) weather cycle that impacts weather around the Pacific, indeed around the globe, is likely to be the strongest on record, according to Professor Neville Nicholls, current President of the Australian Meteorological and Oceanographic Society.

"The Queensland floods are caused by what is one of the strongest (if not THE strongest) La Niña events since our records began in the late 19th century . Our understanding of the La Niña and its impacts meant that the Bureau of Meteorology, as early as October, was warning of substantially increased chances of above average rain across eastern Australia. The La Niña is also associated with record warm sea surface temperatures around Australia and these would have contributed to the heavy rains."

"The extent to which any of this (the floods, the warm oceans, or the very strong La Niña) is linked to global warming is unknown, because the requisite studies to test this have simply not been done yet." concluded Professor Nicholls, who is an Australian Research Council Professorial Fellow in the School of Geography & Environmental Science at Monash University.

"The current La Niña in the Pacific Ocean, one of the strongest in the past 50 years, continues to exert a powerful influence on weather around the world, affecting rainfall and temperatures in varying ways in different locations." said a article La Nina-caused woes down under.

Professor Nicholls discussed the case for this year's La Niña being a possible record in his President's column, dated January 7, 2011, of the Australian Meteorological and Oceanographic Society. He states:

we can use the Southern Oscillation Index, or SOI to compare the strength of La Niña episodes across time. The SOI is the standardised difference in surface atmospheric pressure between Tahiti and Darwin. Monthly SOI values are available at Positive values of the SOI (low pressures at Darwin and high pressures at Tahiti) indicate a La Niña event. There is no a priori reason to expect that global warming has necessarily led to long-term SOI changes that would confound our results if we use the SOI to compare historical and recent La Niña events. And values of the SOI are available from the end of the 19th century.

The SOI values confirm that we are in the middle of either the strongest La Niña event on record, or the second strongest. The SOI values for October 2010 and December 2010 were each the largest positive values on record for those months, as was the three-month average October-December 2010. If we take a longer perspective (July-December) then 1917 was stronger than 2010, but 2010 was still the second strongest in the historical record. Using either the October-December or the longer July-December periods, the strong La Niña events on 1973 and 1975 were both ranked as weaker than the 2010 event.

So more rain in store for Queensland and Australia over coming months, and possibly more flooding events.

"Since La Niña events are generally followed, some months later, by global cooling, we can expect cool temperatures for quite some time." concluded Nicholls in his column.

Read his full statement: Are we experiencing the strongest La Niña event on record?, published on January 7, 2011.

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