The formation of the recent cooling in the eastern tropical Pacific Ocean and the associated climate impacts: A competition of global warming, IPO, and AMO

The cooling trend in the eastern tropical Pacific sea surface temperature (SST) during 1979-2008 is examined by using a wide variety of data sets for the ocean and atmosphere. The results show that the cooling trend is statistically significant at the 10% level out of the equator rather than along the equator. Diagnostic analysis indicates that the SST cooling in the eastern tropical Pacific is resulted from a competition of global warming mode, Interdecadal Pacific Oscillation (IPO) mode, and Atlantic Multidecadal Oscillation (AMO) mode. The cooling trend is preliminarily dominated by the phase transition of IPO from positive to negative phases in the year around 1998/1999, which overwhelms the effect of global warming in past three decades. Quantitative estimates based on the average of four different SST data sets indicate that the global warming mode offsets more than half of the cooling effect of IPO mode. The phase transition of AMO during 1990s causes a weak warming trend in the eastern tropical Pacific and partly weakens the cooling, making the trend along the equator less significant. Climate impacts associated with global warming mode, IPO mode, and AMO mode are further examined. The surface air temperature cooling over the eastern tropical Pacific, the easterly wind anomaly along the Pacific equator, the enhanced zonal gradient in sea level pressure over tropical Pacific, and the increased precipitation over the Asian monsoon region during 1979-2008 are dominated by the phase transition of IPO.