Interannual variation of precipitation over the Hengduan Mountains during rainy season

Abstract

ABSTRACTThe present study investigates the interannual variability of precipitation over the Hengduan Mountains (HMs) during rainy season based on daily precipitation dataset of 151 meteorological stations. More HMs precipitation is associated with an anomalous lower level cyclonic circulation over the northern South China Sea (SCS) and the upper level Silk Road pattern (SRP)‐like geopotential height anomalies. Along the north flank of the anomalous cyclonic circulation, easterly wind anomalies weaken climatology winds and prevent further movement of southwest moisture transport, leading to the enhancement of moisture convergence over HMs. Diagnosis shows that anomalous vertical motions are owing to the advection of anomalous temperature by basic zonal winds. The anomalous lower level cyclonic circulation over the northern SCS is related to La Niña‐like sea surface cooling in the equatorial central and eastern Pacific. This cooling adjusts the Walker Circulation, causing positive precipitation anomalies near the SCS, which trigger the anomalous cyclonic circulation as a warm Rossby wave response. The distribution of upper level geopotential height anomalies over the mid‐latitude Asian land resembles the SRP. Due to its barotropic structure, the SRP leads to warm and cold anomalies over the central Asia and the central China, respectively. The advection of anomalous temperature gradient by mean westerlies leads to anomalous ascending motions and more precipitation over HMs.