The Relationship Between Atmospheric Circulation Variability In Indian Monsoon Region And Precipitation Anomalies Of Low Latitude Highlands In China From June To September

Based on the atmospheric circulation reanalysis data of ERA-Interim,precipitation from 136 gauge stations in Low Latitude Highlands(LLH)and outgoing longwave radiation provided by NOAA,the relationship between atmospheric circulation variability in Indian monsoon region and precipitation anomalies of LLH in June-September was studied using statistical method and numerical simulation.The the diagnosis results indicate that,when the Indian summer monsoon trough(ISMT)is weaker than normal,an anomalous anticyclone controls the region from northwestern Indian subcontinent-western Bay of Bengal(BOB),the anomalous anticyclone induces an anomalous cyclone in LLH by forcing out an anomalous divergent circulation.The anomalous cyclone in Yunnan further induces onshore westerly anomalies appearing at the northern of BOB.The monsoon flow,characterized by southwesterly winds is superimposed by the onshore westerly anomalies,therefore increasing the transportation of water vapor from the BOB to LLH.The configuration of anomalous circulation therefore results in a heavier-than-normal precipitation over LLH as a result of convergent anomalous water vapor mixing with anomalous cold air in the same region.When the ISMT is stronger than normal,the opposite configuration of anomalous circulation will cause a less-than-normal precipitation in LLH.The results of several numerical experiments obtained from a linear baroclinic model(LBM)and atmospheric circulation model(ECHAM6)indicate that the atmospheric heat source anomalies in the northwest Indian subcontinent-west of the BOB influence the LLH precipitation in June-September by anomalous vertical circulation associated with the anomalous divergent circulation.The anomalies of atmospheric heat source on LLH could make the most of the Indian subcontinent under the control of anomalous northwesterly(southeasterly)winds and turn to anomalous southwesterly(northeasterly)winds over the northern BOB through a 'pump effect'.The modeling results are consistent with the diagnosis results obtained by composite analysis,indicating that the anomalous divergent circulation in the northwest Indian subcontinent-BOB-LLH is the key physical processes linking the atamospheric circulation variability in Indian monsoon region and precipitation anomalies of LLH in June-September together.