盛夏副高边缘局地暴雨的形成机制研究

The local sudden rainfall under the stable circulation background near the edge of the subtropical high in midsummer has the characteristics of the short duration and large intensity. It is a type of important high-impact weather. However, previous studies did not pay much attention on this kind of rainfall. By the comprehensive technical approach of diagnostic analyses of observation, numerical simulation, statistical-dynamical diagnostic analyses, and the Lagrangian method and associated theoretical derivation of dynamical process for multiple typical rainfall cases, this research project focuses on: (1) identifying the founding process of local atmospheric instability before the occurrence of the rainfall, and searching for new index to estimate the instability for this type of local rainfall; (2) exploring the mechanism responsible for the moisture gather in a short time before rainfall by Lagrangian numerical simulation and the technique of tracking moisture source; (3) deriving the G vector which could depict local vertical motion, direct illustrating the local updrafts before and during the period of rainfall, and trying to reveal the triggering mechanism inducing the uplift; (4) constructing the "precursor" physical variable to predict the occurrence of the local heavy rainfall near the edge of subtropical high. By above analyses for the special instability, moisture, vertical motion conditions to form this type of heavy rainfall, we try to reveal the formative mechanism of the local heavy rainfall near the edge of subtropical high, provide solid theoretical basis and scientific thinking for deep understanding, diagnosing , and forecasting this kind of local heavy rainfall.

盛夏副高边缘稳定环流形势下的局地暴雨，具有突发性强、历时短、强度大的特点，是一种重要的高影响天气，而过去对此类暴雨研究甚少。本项目研究选取此类暴雨的多个典型个例，拟基于观测资料分析和高分辨数值模拟结果，采用动力、统计相结合的诊断方法，并借助最新的拉格朗日分析技术及动力过程理论推导，(1)研究此类暴雨发生前大气不稳定的建立过程，并提出适用于描述其大气不稳定的新判据；(2)采用基于拉格朗日数值模拟的水汽源区追踪和诊断技术，认识此类暴雨发生前的水汽快速汇聚机制；(3)推导并采用可描述局地大气垂直运动的G矢量，直观显示此类暴雨发生前和降水过程中雨区的垂直运动发生发展过程，揭示引起该上升运动的暴雨启动机制；(4)基于上述研究，构建可预示该类暴雨发生的"前兆性"物理变量。通过对以上暴雨形成物理条件的细致研究，真实揭示副高边缘局地暴雨形成机制，为该类暴雨研究提供坚实的理论基础，并为其科学预报提供新思路。

本项目选取盛夏副高边缘局地暴雨的多次典型天气过程，基于观测资料分析和高分辨数值模拟结果，采用动力、统计相结合的诊断方法，并借助拉格朗日分析技术及动力理论推导，(1)发展了适用于描述副高边缘局地暴雨中大气不稳定的新判据，来识别该类暴雨发生之前局地大气不稳定的建立过程，这无论对大气不稳定研究还是对该类暴雨的预测理论发展都有贡献；(2)基于欧拉和拉格朗日方法，追踪和识别副高边缘局地暴雨的水汽输送路径和源区，探讨水汽快速汇聚机制，解析该类暴雨的水汽供给问题；(3)从能量和动量变化的角度，揭示了副高边缘局地暴雨中对流发展的能量和动量源，构建了对流活跃度新判据，从促进暖湿空气抬升(激发垂直运动)的能量和动量源判别对流发展潜势、识别暴雨启动机制；(4)发展了可预示副高边缘局地暴雨的前兆性物理变量，如修正的理查逊数和二阶位涡等，这些变量可直接用来诊断这类暴雨发生。通过这些研究，从该类暴雨发生的不稳定环境及水汽和垂直运动条件等揭示副高边缘局地暴雨的形成机制，并构建了暴雨发生的指示性物理变量，为科学预报提供了新思路。