Thermal Configuration Of The Bay Of Bengal-Tibetan Plateau Region And The May Precipitation Anomaly In Yunnan

In this paper,we study the relationship between the thermal configuration of the Bay of Bengal(BOB)–Tibetan Plateau(TP)region and the precipitation anomaly in Yunnan in May using ERA-Interim reanalysis data and precipitation data for May from 125 meteorological stations across Yunnan for 1979–2014.Model runs with a linear baroclinic model suggest physical consistency.Results from the analysis indicate that:(1)The interannual variability of May precipitation in Yunnan is significantly modulated by the BOB–TP thermal configuration.The thermal conditions over the BOB mainly impact the May precipitation anomaly in Yunnan via changes in water vapor transport from the eastern BOB northeastward to southwestern Yunnan.The second factor influencing precipitation anomalies relates to the characteristics and variability of cold air transport from the TP to northeastern Yunnan.(2)When the BOB(the TP)is occupied by positive(negative)diabatic heating,thermal gradient with a warmer(colder)center over the BOB and a colder(warmer)center over the TP is established,and more(less)-than-normal precipitation in Yunnan will occur in May.This relationship can persist from the April to the current May to some extent;therefore,the BOB–TP thermal configuration in April could be used to forecast May precipitation in Yunnan.(3)When a positive latent-heat anomaly occurs in the BOB,and a negative sensible-heat anomaly and negative radiation-heat anomaly occur over the TP,a thermal gradient is established with a warmer center over BOB and a colder center over the TP,and remains from early April to the end of May through the two positive feedbacks.The southwesterly anomalies caused by the persistently positive thermal configuration of the BOB–TP extend from the BOB and the western Indochina Peninsula northeastward to southwestern Yunnan,and the northeasterlyanomalies induced by the same thermal configuration prevail from the west edge of the TP southwestward to the northeastern Yunna.The persistent convergence zone continuously occupies Yunnan,and leads to more-than-normal May precipitation in Yunnan.By contrast,less than normal precipitation occurs in Yunnan when a thermal gradient with a colder center over the BOB and a warmer center over the TP is established and persists from April to the end of May.(4)The modeling results and variances explained further suggest that the positive BOB–TP thermal configuration induces a stronger-than-normal May precipitation in Yunnan through significantly converging the warm-wet airflow from the BOB with the cold airflow from the eastern TP in Yunnan.