Changes in spatial and temporal properties of Pacific warming

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Tuesday, 19 January 2010
Hye-Mi Kim, Georgia Institute of Technology, Atlanta, GA; and P. J. Webster

Two different flavors of tropical Pacific Ocean warming events have been identified, each with its distinctive teleconnection patterns including opposite impacts on tropical cyclone activity in the North Atlantic. They are shown to have different spatial and temporal ocean-atmosphere properties in their developing and decaying phases. The eastern Pacific warming (EPW), identical to the conventional El Niņo, is associated with basin-scale wind and thermocline variation. In contrast, the central Pacific warming (CPW, or Modoki), where maximum sea-surface temperature (SST) anomalies are located near the dateline, is associated with local coupling processes. Although the occurrence of the total number of warm events has stayed the same, the number of CPW events has been increasing, especially since the early 1990s. The long term change of the SST off the equator in the eastern Pacific makes weaker pressure gradient, and it leads weakening the equatorward meridional wind and equatorial easterly winds. The enhanced westerly wind anomaly over the central Pacific demises the zonal SST gradient that makes a favorable condition for CPW occurrence.