The influence of the Madden-Julian Oscillation activity anomalies on Yunnan's extreme drought of 2009-2010  

作　　者：LU JunMei JU JianHua REN JuZhang GAN WeiWei 

机构地区：[1]Chinese Academy of Meteorological Sciences,Beijing 100081,China [2]Yunnan Provincial Meteorological Service,Kunming 650034,China [3]Yunnan Institute of Meteorology,Kunming 650034,China [4]Department of Atmospheric Sciences,Yunnan University,Kunming 650091,China

出　　处：《Science China Earth Sciences》2012年第1期98-112,共15页中国科学（地球科学英文版）

基　　金：supported by Union Fund of the National Natural Science Foundation of China and Yunnan Province (Grant No. U0833602);Special Project of the China Meteorological Administration (Grant No. GYHY200906017);National Natural Science Foundation of China (Grant Nos. 40705026, 40805036 and 40905043);Basic Research Fund of the Chinese Academy of Meteorological Sciences (Grant No. 2010Z001);Science and Technology Program of Yunnan Province for the Development of Society (Grant No. 2009CA023)

摘　　要：Yunnan Province of China suffered a record-breaking drought that persisted from autumn 2009 into spring 2010. The present study examined the physical causes of this extreme drought event in terms of persistent anomalies of intraseasonal oscillation in the tropical atmosphere （the Madden-Julian Oscillation hereafter the MJO）. The results show that the occurrence of severe drought in Yunnan was caused directly by deficient rainfall lasting from the summer of 2009 to the spring of 2010. Further ex- ploration reveals a persistent positive variation of MJO index 1 from June to October. Accordingly, the convective activity over the Bay of Bengal （BOB） weakened continuously, and then an anomalous descending airflow was induced over the tropi- cal Indian Ocean, resulted in the anomalous weakening of vertical Asian monsoon circulation in South Asia. Consequently, the transport of water vapor from the tropical Indian Ocean to Yunnan decreased abnormally, leading to persistent below-normai rainfall over Yunnan from summer to autumn in 2009. As a result, a severe drought began to appear in autumn. In the winter of 2009-2010, MJO index 1 remained persistently positive, indicating the continuous weakening of convective activity over the BOB. The atmospheric circulation associated with the persistent positive anomalies in the MJO also demonstrated anomalous patterns. Specifically, there was an anomalous high-pressure ridge stretching from South Asia through the Tibetan Plateau and into the western part of southwestem China. This indicates that the atmospheric circulation over Yunnan was dominated by vertical descending airflow in the high-pressure ridge. Simultaneously, the India-Burma trough was weakened, which resulted in unfavorable conditions for the transport of water vapor from the BOB to Yunnan, causing the observed persistent deficient precipitation in winter and the subsequently intensified drought. Therefore, the persistent anomalies in MJO activity in the tropical atmosphere played an important role in the ocYunnan Province of China suffered a record-breaking drought that persisted from autumn 2009 into spring 2010. The present study examined the physical causes of this extreme drought event in terms of persistent anomalies of intraseasonal oscillation in the tropical atmosphere (the Madden-Julian Oscillation hereafter the MJO). The results show that the occurrence of severe drought in Yunnan was caused directly by deficient rainfall lasting from the summer of 2009 to the spring of 2010. Further exploration reveals a persistent positive variation of MJO index 1 from June to October. Accordingly, the convective activity over the Bay of Bengal (BOB) weakened continuously, and then an anomalous descending airflow was induced over the tropical Indian Ocean, resulted in the anomalous weakening of vertical Asian monsoon circulation in South Asia. Consequently, the transport of water vapor from the tropical Indian Ocean to Yunnan decreased abnormally, leading to persistent below-normal rainfall over Yunnan from summer to autumn in 2009. As a result, a severe drought began to appear in autumn. In the winter of 2009-2010, MJO index 1 remained persistently positive, indicating the continuous weakening of convective activity over the BOB. The atmospheric circulation associated with the persistent positive anomalies in the MJO also demonstrated anomalous patterns. Specifically, there was an anomalous high-pressure ridge stretching from South Asia through the Tibetan Plateau and into the western part of southwestern China. This indicates that the atmospheric circulation over Yunnan was dominated by vertical descending airflow in the high-pressure ridge. Simultaneously, the India-Burma trough was weakened, which resulted in unfavorable conditions for the transport of water vapor from the BOB to Yunnan, causing the observed persistent deficient precipitation in winter and the subsequently intensified drought. Therefore, the persistent anomalies in MJO activity in the tropical atmosphere played an important role in the occurrence of

关 键 词：YUNNAN extreme drought MJO persistent anomalies 

分 类 号：P433[天文地球—大气科学及气象学] P315.5