Response of the anomalous western North Pacific anticyclone during El Niño mature winter to global warming

Abstract

The western North Pacific subtropical anticyclone (WNPAC) usually fully develops during El Nino mature winter, and it is a key system connecting East Asian climate to ENSO. Based on a comparison between the RCP8.5 and the historical experiment of 30 coupled models from the CMIP5, we find that the response of the intensity in the anomalous WNPAC during El Nino mature winter remains almost unchanged under global warming. Taken the anomalous WNPAC as a two-step response to the diabatic heating anomaly over the equatorial central-eastern Pacific, numerical experiments based on GFDL_dry model and diagnoses are performed to explore the underlying mechanisms. The results demonstrate that the competition between the enhanced diabatic heating anomaly over the equatorial central-eastern Pacific and the enhanced mean state static stability results in a weakly enhanced low-level northeasterly wind anomaly over the WNP. Under an enhanced negative meridional gradient of the mean state low-level specific humidity, the negative moist enthalpy advection anomaly is enhanced over the WNP, which favors the enhanced negative precipitation anomaly. The negative precipitation anomaly over the WNP is thus enhanced due to atmospheric internal processes rather than the changed local SST anomaly. Finally, the competition between the enhanced local diabatic heating anomaly over the WNP and the enhanced mean state static stability results in an almost unchanged anomalous WNPAC.