Interdecadal change in the principal mode of winter–spring precipitation anomaly over tropical Pacific around the late 1990s

Abstract

Evidence show that the dominant mode of winter–spring precipitation anomaly over the tropical Pacific experienced a pronounced interdecadal change around 1998. Based on the extended empirical orthogonal function (EEOF) technique, a zonal dipole pattern of precipitation anomaly is dominant during the pre-1998 period. Corresponding to a positive principle component (PC1), positive precipitation anomaly over the equatorial eastern Pacific (EP) decays eastward from winter to spring, which is identified as an eastward-decaying EP mode. During the post-1999 period, there is a zonal triple pattern with enhanced precipitation over the equatorial central Pacific (CP) and reduced precipitation over the western North Pacific and equatorial southeastern Pacific with a positive PC1. This triple pattern of precipitation anomaly maintains with decreasing amplitude from winter to spring, which is called the fixedly-decaying CP mode for short. Such interdecadal shift is controlled by differing sea surface temperature (SST) anomaly pattern. The interdecadal differences of winter–spring wind stress and thermocline over tropical Pacific might result in the interdecadal change in the SST anomaly and then precipitation mode, via modulating physical oceanic feedback processes. In addition, the effect of two distinct precipitation modes on the North Pacific teleconnection and North American surface temperature anomaly was strikingly different. Before 1998, the eastward-decaying EP mode might induce a significant tropical Northern Hemisphere (TNH)-like teleconnection only in winter, leading to a north-to-south pattern of North American temperature anomaly, which is greatly limited in spring. After 1999, a northwest-to-southeast response of North American temperature sustains from winter to spring, resulting from the maintenance of the Pacific-North America (PNA)-like pattern, simulated by the fixedly-decaying CP mode.