一个干侵入参数及其应用

A dry intrusion parameter and its application

中文关键词:  干侵入， 参数， 等熵分析

英文关键词:Dry intrusion, Parameter, Isentropic analysis

中文摘要:

      鉴于干侵入在气旋的爆发性发展、冷锋的演变等方面起着重要的促进作用，因此，文章详细分析了一次北方暴雨中的干侵入特征。分析发现，干侵入在此次降水事件中一直维持，而且降水随干侵入的增强而加强，干侵入推动了降水区的东南向移动。在McNulty早期工作的基础上，借鉴Doswell以及Schultz等发展的IM (ingredients based methodology)方法，将其应用于干侵入的研究。文章将过去对干侵入（无论在等压面还是等熵面上）的研究中，用低相对湿度、冷平流、高位涡来表征干侵入气流的这些单个物理量综合起来，用一个简单、使用方便的物理参数来表征干侵入。这是以往暴雨研究中的IM理论方法在干侵入研究领域的新尝试。文章用新的干侵入参数，在等熵面上分析了实际降水过程中干侵入的演变。分析表明，干侵入参数能够较好地量化干侵入强度，指示卫星云图和水汽图像上干区的演变。通过等熵面与相应气压层的对比分析，发现等熵和等压面上的分析比较一致，等熵面上的干侵入在高层比低层强度大。由垂直剖面图的分析可见，干侵入气流位于低层暖湿气流上方，这就使得垂直方向上出现位势不稳定，有利于降水发生。这样，我们就可以通过干侵入参数来找干侵入区，关注干侵入区附近的不稳定区，来对降水做出预测，从而提高降水预报的准确率。

英文摘要:

      Dry intrusion plays an important role in the explosive development of cyclones and the evolution of cold fronts.Characteristics of dry intrusion during a rainfall event that occurred in Northern China is analyzed in detail. It is found that dry intrusion maintained during the precipitation periods. The intensity of precipitation increased with the increasing dry intrusion, which pushed the rainy region southeastwards. Based on a previous study by McNulty, the IM (ingredients based methodology) developed by Doswell, Schultz and Schumacher is utilized in this study. In this paper, all the physical representations such as low relative humidity, and cold advection, and high potential vorticity (on either isobaric or isentropic surfaces ) defined in the past studies of dry intrusion are combined into a simple and convenient parameter to characterize dry intrusion. This is a new attempt to extend the IM method in the research of heavy rainfall related to dry intrusion. The new dry intrusion parameter is used to analyze the isentropic evolution of dry intrusion during a rainfall event. The analysis shows that, this parameter can better quantify the intensity of dry intrusion and diagnose its evolution through using satellite infrared and water vapor imageries. By the contrast results on the isentropic surface and the corresponding isobaric surface, it is inferred that the analyses of dry intrusion on both surfaces are consistent with each other. By the isentropic analysis of dry intrusion, cold and dry air at upper levels overruns that in the lower troposphere, where moist and warm air is located. Thus, potential instability is built up in the vertical direction, which is in favor of the occurrence of precipitation. Therefore, we may look for dry intrusion regions by tracing strong signals of the dry intrusion parameter, and focus on the instability near dry intrusion regions in precipitation forecasting. This method will aid to improve the accuracy of precipitation forecasting.