利用综合观测数据1°×1°FNL和2.5°×2.5°NCEP再分析资料、以及卫星云顶黑体辐射温度资料(TBB),对2015年11月广西出现的三次暴雨过程(8日、11—12日和20日)的850 h Pa水汽通量散度及水汽输送特征进行了对比...利用综合观测数据1°×1°FNL和2.5°×2.5°NCEP再分析资料、以及卫星云顶黑体辐射温度资料(TBB),对2015年11月广西出现的三次暴雨过程(8日、11—12日和20日)的850 h Pa水汽通量散度及水汽输送特征进行了对比分析。8日和20日暴雨的低层水汽主要来自南海,11—12日连续暴雨的水汽来自南海和孟加拉湾。暴雨前后TBB的分析表明,在暴雨发生前2～3 d,孟加拉湾对流发展到最强,孟加拉湾对流对广西秋季暴雨具有前兆信号特征。暴雨前后TBB时空剖面表明,暴雨发生前孟加拉湾对流有向广西波动传播的特征。模式敏感性实验显示,当关闭孟加拉湾对流2～3 d后,广西48 h累计雨量减小。展开更多
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 anomali...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 occurrence of the extreme drought event in Yunnan in 2009-2010.展开更多
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)+2 种基金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)
文摘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 occurrence of the extreme drought event in Yunnan in 2009-2010.
