华南降水准双周振荡在前夏和后夏的不同特征分析及其机理研究

Rainfall in the eastern China is of notable intraseasonal variability. Better understanding of the intraseasonal variability in the eastern China rainfall and the corresponding physical mechanism helps to improve the ability of the prediction of the eastern China rainfall. According to the previous studies, the quasi-biweekly oscillations (QBWO) of South China (SC) rainfall during early and late summers are probably distinct. Our previous results also suggest that it is necessary to investigate the rainfall anomalies over SC during early and late summers separately. Therefore, this project is to investigate the distinct features of the QBWOs of SC rainfall during early and late summers. The influence of the tropical QBWOs and the large scale circulations in the tropics and extra-tropics on the differences of the QBWOs of SC rainfall between early and late summer is to be studied, and the physical causes of the differences of the QBWOs of SC rainfall between early and late summer are to be revealed. To promote the understanding of the QBWOs of SC rainfall, this project is to separately investigate the interdecadal changes of the QBWOs of SC rainfall during early and late summers in the mid-1990s, since the QBWOs of SC rainfall during summer are significantly enhanced after the mid-1990s, which is revealed recently. The impact of the factors, such as large scale basic flows and sea surface temperatures, on the interdecadal changes of the QBWOs of SC rainfall during early and late summers is to be studied. And the physical mechanism associated with the interdecadal changes of the QBWOs of SC rainfall during early and late summer is to be revealed.

中国东部降水具有显著的季内变率，理解降水的季内变率及其物理机制有助于提高对降水的预报能力。从前人研究成果来看，华南降水准双周振荡很可能在前夏和后夏有所不同。我们以往的研究结果也显示在研究华南降水异常时有必要对前夏和后夏分别研究。因此，本项目将研究前夏和后夏华南降水准双周振荡的不同特征，并探讨热带准双周振荡及热带和热带外大尺度环流对华南降水准双周振荡前、后夏差异的影响，确认导致华南降水准双周振荡前、后夏差异的物理原因。为了加深对华南降水准双周振荡的认识，本项目根据最近的研究结果，夏季华南降水准双周振荡在1990s中期以后显著增强，进一步研究前夏和后夏华南降水准双周振荡的年代际变化，分析大尺度背景因子，如大气环流基本态和海温等，对前夏和后夏华南降水准双周振荡年代际变化的影响，揭示前夏和后夏华南降水准双周振荡年代际变化的物理机制。

华南地区夏季降水较多，并具有显著的季内变率，揭示华南降水的季内变率特征及其物理机制有助于提高对降水的认识。为提高降水预报能力打下基础。前人研究表明，影响华南降水的气候系统在前夏和后夏有所不同。因此，本项主要研究了前夏和后夏华南降水准双周振荡的特征及其物理过程。分析结果表明，前夏和后夏华南降水都具有显著的10-25天振荡。其对应的降水物理过程和季内振荡来源有所不同。前夏事件受到在10°-20°N从热带西北太平洋和南海向西传播的热带波动影响，其通过经向次级环流影响华南降水，还受到中高纬自西北向东南传播的波列的影响。后夏事件主要受到从热带西北太平洋想西北传播的季内振荡的影响。1990s中期前后，前夏和后夏降水季内振荡事件的降水物理机制和季内振荡来源都发生了变化。前夏事件1990s中期前主要受到在30°N附近由西向东传播的准正压波列的影响，1990s中期后此波列影响较小。后夏事件1990s中期前受到的是在20°N附近从热带西太平洋向西传播的波列，而1990s中期后受到的是赤道太平洋西北传的波列的影响。这些年代际变化可以部分归咎于气候态前夏急流的减弱和后夏赤道西太平洋辐合的增强。本项目还发现中国白天，夜晚和复合热浪的频率、强度、影响面积在1990s中期以后都显著的增加。其中复合热浪的3个变量是变化幅度最大的。人类活动影响对于中国热浪在1990s中期的变化具有非常大的贡献。其中，温室气体变化对模拟的三种热浪的频率、强度和影响面积的年代际增加其决定性的作用，而气溶胶变化的影响相对较弱，它使得东北地区白天热浪的频率和强度增加，而东南地区的白天热浪频率和强度减少。未来21世纪中期在RCP4.5情景下，三种热浪将会变得更频繁、强度更大，持续时间更长。复合热浪的变化幅度最大。热浪未来的变化远大于年代际变化。