西风槽背景下华北暴雨发生前的征兆及其触发机制研究

We study the instability characteristics in Huabei region, China just before the torrential rain occurrence( 6-12 hours before). Here the instability is a kind of mixed-type instability, which include the interactions among the baroclinic instability, convective instability and symmetrical instability. We study and calculate the vertical motion just before the heavy rainfall under the background of the westerly trough, and then ensure the vertical motion region. We study the features of the moisture transportation and the convergence just before the heavy rain under the setting of the westerly trough, including the source of the moisture, the channel and process of the moisture transport, the vertical transport and the convergence of moisture, the location and height of the vapor phase transition and so on. In addition, we study the triggering mechanism of the torrential rainfall in Huabei region, China under the setting of the westerly trough, which consists of the dry intrusion from the mid- high levels of the atmosphere, the wind shear, gravity wave and the orographic forcing. Through the data diagnosis and analysis, the numerical simulation and the dynamic study, we try to find and reveal the symptom and the triggering mechanism just before the heavy rainfall, thus we can understand more about the occurrence and the development of the torrential rainfall in Huabei region, China. We attempt to reveal objectively and really the whole development of the torrential rainfall of Huabei region, so that we build up theory foundation for the more accurate forecast and provide the more scientific and innovate methods to forecasters.

研究华北暴雨发生前（6-12小时以下均为此）华北地区的不稳定特征及性质。这里主要包括研究斜压不稳定、对流不稳定与对称不稳定之间相互作用的混合型不稳定特征及性质。研究并计算西风槽背景下华北暴雨发生前的垂直运动，并确定明显垂直运动区。研究西风槽华北暴雨发生前水汽的输送及集中的特征。这包括水汽来源、水汽输送通道、水汽输送过程、水汽垂直输送及集中的特征，以及水汽相变发生的位置及高度等。研究西风槽背景下华北暴雨触发机制。这里包括由大气中高层的干侵入、风切变、重力波及地形强迫等对暴雨的触发机制。通过对西风槽背景下华北暴雨发生前的资料诊断分析和数值模拟，以及动力研究，来寻找并揭示西风槽背景下华北暴雨发生前的征兆和触发机制，以此来深入认识西风槽背景下华北暴雨发生、发展特点。力求真实客观揭示西风槽背景下华北暴雨的形成过程，为提高华北暴雨的预报水平奠定坚实的理论基础，并提供科学的预报新思路。

华北暴雨主要是由西风槽引起的，所以研究华北西风槽背景下的暴雨具有重要意义，对华北减少暴雨灾害以及水资源利用具有重要贡献。主要研究了华北暴雨发生前的不稳定问题、水汽集中问题、垂直运动状况，以及干侵入问题。在这4个方面我们做了很成功的研究。研究了华北暴雨发生前的不稳定，华北暖区暴雨主要是对流不稳定引起的，锋面降水过程主要是对称不稳定引起的。不仅用准地转理论计算了准地转垂直运动，并用非地转位势及非地转温度计算了由非地转引起的垂直运动。研究了华北暴雨发生前的水汽输送及集中的特征，主要包括水汽来源、水汽输送通道、水汽集中等。研究了华北暴雨发生过程中的干侵入，指出高层冷空气干侵入到湿不稳定区是引起华北中尺度对流发展的主要触发机制。