Asymmetric impacts of El Nino-Southern Oscillation on the winter precipitation over South China: the role of the India-Burma Trough

The winter precipitation over South China (SCWP) can exert great impacts on the local ecosystem and human livelihood. Previous studies suggested that the inter-annual variability of SCWP can be affected by the El Nino-Southern Oscillation (ENSO) via the Northwest Pacific anticyclone (NWPAC). The present study investigates the role of the India-Burma Trough (IBT) in mediating the teleconnection between ENSO and the SCWP. During the El Nino mature winter, the slowdown of Walker circulation is evident over the tropical Indian Ocean (TIO). The low-level easterly wind anomaly is pronounced from the warm pool to the western TIO, which turns into the westerly wind anomaly over the northern TIO basin and then enhances IBT. Meanwhile, the Kelvin wave in the upper troposphere stimulated by El Nino propagates eastward toward Indian Ocean and induces the tropospheric warming over TIO. The resultant increase of the meridional temperature gradient leads to the southward shift of the westerly jet stream which favors the strengthening of IBT and the increase of SCWP. It is further shown that the IBT change is unclear in La Nina. This nonlinear feature can be largely attributed to the asymmetry in both ENSO amplitude and ENSO-related circulation anomalies. The present findings highlight the role of IBT, in addition to the well-known NWPAC, in bridging ENSO and SCWP.