华南前汛期开汛三种类型的变化特征及其影响机制

The first rainy season over South China is a regional, explosive, and continuous heavy rainfall process. The onset date of the first rainy season over South China is the beginning of first precipitation concentration period during one year. Our early research shows that there exist obvious three onset types, namely that from north to south, from south to north, and a comprehensive eruption at the same time, which involved the interannual and intraseasonal oscillation scale effect. Base on multiscale view, using statistical analysis method to understand the distribution characteristics of the structure of three-dimensional characteristics of thermodynamic and dynamic factors of the three onset types, revealing the key physical processes the atmospheric circulation (the arctic oscillation, the heat source of the Tibet plateau and the northwest Pacific subtropical high, etc.) and air-sea interaction (mainly ENSO, the kuroshio) impact on the three onset types during first rainy season over South China. It is analyzed the difference of the direction of propagation, the source of disturbance and the strength of the atmospheric low frequency oscillation affecting the three onset types. The important main contribution physical process of intraseasonal variation will be explored. According to analysis data results and design experimental scheme, using ECHAM a numerical simulation of the atmospheric general circulation model to study the influence mechanism. This project will be understood more comprehensively and systematically variation of the precipitation during the first rainy season over South China.

华南前汛期是一个区域性、爆发性和连续性的强降水过程，华南前汛期开始日期是年内第一个降水集中期之始。前期研究表明，华南前汛期开汛存在明显的由北往南、由南往北和全面同时爆发三种类型，涉及到年际和季节内振荡尺度影响问题。本项目采用多尺度观点，首先运用统计分析方法了解华南前汛期开汛三种类型对应的热力和动力因子在三维空间上的结构分布特征，揭示大气环流（北极涛动、青藏高原热源和西北太平洋副热带高压等）和海气相互作用（主要是ENSO、黑潮区）影响华南前汛期开汛三种类型的关键物理过程。分析对比影响华南前汛期开汛三种类型的大气低频振荡强度、扰动来源和传播方向的不同，探讨起主要贡献的物理影响过程。其次，根据资料分析结果设计实验方案，采用ECHAM大气环流模式进行数值模拟，研究其影响机制。本项目将是对华南前汛期降水变化的一个更全面、更系统的认识。

华南前汛期是一个区域性、爆发性和连续性的强降水过程。科学家普遍认为华南前汛期降水最早从江南开始，由北往南传播。本项目得到了华南前汛期的三种开汛类型，即由北往南传播型（I类）、由南往北传播型（II类）和全面爆发型（III类），打破了传统的认知。资料分析和模式模拟表明，在年际尺度上，I类表现为前冬海温呈现中太平洋异常冷、热带西太平洋和黑潮异常暖和北太平洋异常冷的“-、+、-”三极异常分布、北正南负的西太平洋遥相关分布和北极涛动（AO）负位相的异常分布型。II类表现为前冬热带海温呈现类La Nina分布、黑潮海温异常偏冷、正欧亚（EU）遥相关分布和AO正位相的异常分布型。III类表现为前冬中东太平洋和黑潮海温异常偏暖和南半球环状模异常偏弱异常分布型。在10-30天（ISO）尺度上，I类，200hPa高层波通量主要表现与东大西洋遥相关型密切相关的北非-东亚急流波列的调整，促使南支槽发展。与之伴随的是低层850hPa为东亚-北太平洋中高纬到华南的异常气旋-反气旋-气旋东南向移动的波列。II类，高空波列主要由北支EU遥相关型和南支北非-东亚急流两支波导共同作用促进华南高空槽的发展。低层由10-30天尺度的由南往北传播的波列和30-60天尺度正涡度平流引导的对流向北传播共同作用。III类，高空没有明显波列传播，主要表现为中高纬的阻塞形势。低层也没有明显的波列传播，主要来自孟加拉湾和南海的异常西南气流加强。水汽诊断表明，由平均环流引起的ISO水汽平流和ISO环流引起的平均水汽平流辐合促使I类和II类开汛。天气涡旋引起的水汽平流促使III类开汛。I类与MJO第3位相（强对流位东于印度洋）有密切关系，孟加拉湾南支槽偏强，AO 为正位相。II类和III类与MJO关系不明显。本项目加深了对华南前汛期开始的科学认知，对提升华南前汛期短期气候预测水平有重要意义。