Cause of severe droughts in Southwest China during 1951–2010
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The cause of severe droughts over the Southwest China (SWC) during the local dry season is investigated based on the station rainfall data and the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data during 1951–2010. The droughts are in general consistent with local anomalous descent in the middle troposphere. The diagnosis of the vertical motion (omega) equation indicates that the local descent is primarily maintained by the anomalous cold temperature advection processes. Both the advection of anomalous temperature by mean wind and the advection of mean temperature by anomalous wind contribute to maintaining the anomalous descent over the SWC region. A composite analysis shows that the circulation anomaly over SWC is induced by remote forcing from the tropical Pacific and North Atlantic Oceans. During La Niña years, enhanced heating over the Maritime Continent induces anomalous downward motion over SWC through the connection of local Hadley circulation. Adiabatic warming associated with the downward motion helps to set up and maintain the local anomalous anticyclone. Another possible route is through the North Atlantic-Asia teleconnection, in which downstream Rossby wave energy propagation plays a crucial role. A negative-phase North Atlantic Oscillation may trigger a large-scale wave train pattern that induces an anomalous anticyclone over the subtropical Asia and promotes the dry condition over SWC.
KeywordsRainfall Drought Southwest China The tropical Pacific North Atlantic Oscillation
This work was supported by the Chinese MoST (Grant No. 2010CB950300), the National Natural Science Foundation of China (Grant No. 41306030 and 4137603), the NSF (Grant No. 40730842), and the Fundamental Research Funds for FIO, SOA, China (Grant No. 2013G03). TL acknowledged support from NSF AGS-1106536 and ONR N000141210450. This is SOEST contribution number 9059 and IPRC contribution number 1035.
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