An Episodic Weakening in the Boreal Spring SST-Precipitation Relationship in the Western Tropical Pacific since the Late 1990s

Abstract

We found that a positive sea surface temperature (SST)-precipitation relationship in the western tropical Pacific (WTP) during boreal spring, in which higher SSTs are associated with higher precipitation, episodically weakens from the late 1990s to the early 2010s. During 1980-98, warm SSTs induce positive precipitation and low pressure in the WTP. The associated enhanced convection dampens the initial warm SSTs by reflecting incoming solar radiation. The reduced incoming solar radiation into the ocean leads to a SST cooling tendency. In contrast, the associated southwesterly wind anomalies reduce oceanic mixing by decreasing the mean wind, contributing to an SST warming tendency, though relatively small. Therefore, the cloud-radiation effect is a dominant process of the negative SST tendency. By contrast, during 1999-2014, although an SST cooling tendency is similarly induced by warm SST anomalies, the cooling tendency is enhanced by anomalous ocean advection, as a result of enhanced easterly wind anomalies in the southern part of the WTP. This results in a weakening of a positive relationship of the SST and precipitation during 1999-2014. As such, the associated anomalous convective heating in the WTP during 1999-2014 is weak, changing the atmospheric teleconnection patterns in the midlatitude and surface air temperature anomalies in western North America and northeastern Eurasia.