The effects of the Indo-Pacific warm pool on the stratosphere

Abstract

Sea surface temperature (SST) in the Indo-Pacific warm pool (IPWP) plays a key role in influencing East Asian climate, and even affects global-scale climate change. This study defines IPWP Nino and IPWP Nina events to represent the warm and cold phases of IPWP SST anomalies, respectively, and investigates the effects of these events on stratospheric circulation and temperature. Results from simulations forced by observed SST anomalies during IPWP Nino and Nina events show that the tropical lower stratosphere tends to cool during IPWP Nino events and warm during IPWP Nina events. The responses of the northern and southern polar vortices to IPWP Nino events are fairly symmetric, as both vortices are significantly warmed and weakened. However, the responses of the two polar vortices to IPWP Nina events are of opposite sign: the northern polar vortex is warmed and weakened, but the southern polar vortex is cooled and strengthened. These features are further confirmed by composite analysis using reanalysis data. A possible dynamical mechanism connecting IPWP SST to the stratosphere is suggested, in which IPWP Nino and Nina events excite teleconnections, one similar to the Pacific–North America pattern in the Northern Hemisphere and a Rossby wave train in the Southern Hemisphere, which project onto the climatological wave in the mid–high latitudes, intensifying the upward propagation of planetary waves into the stratosphere and, in turn, affecting the polar vortex.