中文摘要：

本文将2008年上海“8.25”暴雨过程的WRF中尺度数值模式模拟结果作为实况资料集,应用EOF（Empirical Orthogonal Function）方法对该资料集进行诊断,以探讨将该方法应用于暴雨p中尺度系统的可行性.主要结论有：当数值模式输出足够稠密、精细的样本,能够较好反映实况时,利用EOF方法对天气尺度和α、β中尺度系统的天气过程进行诊断是可行的.对本文的暴雨过程,EOF分解位势偏差场的前三个模态分别反映了α中尺度中端、低端和β中尺度天气系统的演变特征,分别对应于波长和振荡频率不同的驻波波列.其可分别称之为暴雨背景模态、暴雨系统模态和暴雨雨团模态.各波列物理性质不同,分别属于准地转的Rossby波、准平衡的涡旋波和非平衡的重力惯性波.天气系统EOF分解的物理本质为：可将一个变形和移动的天气系统分解为若干个具有不同物理性质且时空尺度不同相互独立的模态（驻波波列）.这有助于明确和深化对天气系统的认识.EOF分解能够进行天气系统的尺度分离,且分离后得到的各种尺度的天气系统是独立和有特定物理意义的,这更体现了该尺度分离方法的优点.本文中当EOF分解后各波列（模态）在某地时空指数发生三波锁相,且该地的位势表现为低空为负、高空为正,同时低层位势急剧降低时,则有可能在此处发生暴雨.

英文摘要：

Using empirical orthogonal function （EOF） expansion, this paper analyzes the Weather Research and Forecasting （WRF） simulative data of the torrential rain occurring on August 25 of 2008 to explore the possibility of EOF expansion for diagnosing a meso-Dseale torrential rain system. The conclusions show that when sufficiently fine data are consistent with real data, it is possible to diagnose mesoscale systems with EOF expansion. The preceding three modes of EOF expansion reflect the evolvement characteristics of various-scale weather systems and correspond to various wave trains with various wavelengths and oscillation frequencies： ambient mode, torrential rain system mode, and rain clusters mode. The various waves are attributed to quasi-geostrophic Rossby, quasi-equilibrium eddy, and non-equilibrium gravity inertia waves, respectively. The physical essence of EOF expansion for a weather system is that a transformative weather system with locomotion can be separated to several mutually unattached modes, or wave trains, that differ in physical characteristics, which contributes to a better understanding of the weather system. Scale separation for weather systems is an advantage of EOF expansion because separate weather systems are unattached and have particular physical characteristics. When the space-time indices of different wave trains are in phase lock, a strongly convective precipitation will occur in the appropriate weather condition.