Whereas La Niña in 2010 was moderate, the associated Western North Pacific (WNP) anticyclone was extremely strong and exhibited an unusual northward and westward shift, resulting in extreme warm and dry conditions in Japan and Northeast Asia. Data analysis and numerical experiments were used to investigate the roles of sea surface temperature anomalies (SSTA) and particularly the record-breaking warm SST in the Atlantic in contributing to this unusual WNP anticyclone. In addition to the Gill-type anticyclonic response to the cold SST in the equatorial central Pacific, which partially explains the anomalous WNP anticyclone, the warm SST in the North Indian Ocean (NIO)/Equatorial Atlantic (EA) forced local/remote vertical overturning circulation, which in turn caused the enhancement and westward shift of the WNP anticyclone. However, the warm SST in the North Atlantic (NA) affected the WNP anticyclone differently than the tropical SSTA. It induced 2 branches of an extratropical wave-like disturbance that propagated downstream and merged in the WNP to result in a barotropic anticyclonic anomaly in the WNP north of the expected position of the WNP anticyclone. This suggests that the strong, downstream-propagating wave activity caused the northward shift of the WNP anticyclone in summer 2010.
關聯:
2012 American Geophysical Union (AGU) Fall Meeting，Organised by AGU，2012-12-03~07
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