Synoptic and Mesoscale Analyses of Heavy Precipitation Events During TAMEX

9421060陈在本项目中，将根据数值模式的结果和台湾地区中尺度试验(TAMEX)期间收集的资料，研究有利于TAMEX期间强降水发展的天气尺度、中尺度和局地过程。当梅雨锋接近台湾岛时，锋前西南季风气流(或低空急流)带来了来自南方的温暖潮湿的不稳定空气。除了低层抬升(地形和锋面)，高空强迫(与分流气流有关的高层辐散或与急流系统有关的锋生强迫)的存在是发展亚热带大范围暴雨所必需的。在本研究中，我们将基于模型生成的高分辨率数据来诊断一个低空急流。特别是，气旋发生和低空急流发展之间的联系将被进一步研究。此外，我们还将研究高层和低层环流之间的耦合，从而导致大范围降水的发展。天气尺度环流控制着是否会发生大范围的降水，而中尺度环流、局地环流和地形效应则精确地控制着对流发生的时间和地点。我们将利用雷达、飞机和常规资料以及嵌套网格模式来研究台湾地区的锋前中尺度气流。特别是当高空槽/低空急流接近时，我们将重点关注迎风一侧的气流。在锋前西南风气流中，偏南急流沿沿岸偏转，形成有利于深部对流发展的局地辐合带。当锋面移过台湾北部时，偏南气流可能与西北沿海台湾海峡的不偏西南气流汇合，形成有利于深部对流发展的局地辐合带。当锋面移过台湾北部时，偏南气流可能与锋后东北风汇合，并在沿岸形成加强的锋面辐合带。为了评估由日间加热循环引起的热驱动环流对降水的影响，我们将研究岛上不同地区日间循环的降雨特征。此外，我们还将根据在IOP#11期间收集的数据，对锋前西南季风气流作用下的岛上局地环流进行个例研究。

9421060 Chen In this project, the synoptic-scale, mesoscale and local processes favorable for the development of heavy precipitation during TAMEX will be studied based on the results form numerical models and the data collected during the Taiwan Area Mesoscale Experiment (TAMEX). As the Mei-Yu front approached the island of Taiwan, the prefrontal southwest monsoon flow (or the low-level jet) brought in the warm, moist unstable air from the south. In addition to the low-level lifting (orographic and frontal), the presence of upper-level forcings (the upper-level divergence related to diffluent airflow or the frontogenetical forcing associated with a jet-front system) is required for the development of widespread rainstorms in the subtropics. In this study, we will diagnose a LLJ based on the model generated high resolution data. In particular, the link between the cyclongenesis and the development of LLJ will be further investigated. In addition, we will study the coupling between the upper-level and low-level circulations leading to the development of widespread precipitation. The synoptic-scale circulations regulate whether or not widespread precipitation will occur, whereas mesoscale circulations, local circulations and orographic effects govern the details of precisely when and where the convection will occur. We will study the prefrontal mesoscale airflow over the Taiwan area based on radar, aircraft and conventional data as well as a nested grid model. In particular, we will focus on the airflow on the windward side as the upper-level trough/low-level jet approached. In the prefrontal southwesterly flow, the deflected southerly jet along the coast and results in a localized convergence zone favorable for the development of deep convection. As the front moved over the northern Taiwan, the deflected southerly flow may merge with the undeflected southwesterly flow in the Taiwan Strait off the northwestern coast and results in a localized convergence zone favorable for the development of deep convection. As the front moved over the northern Taiwan, the deflected southerly flow may converge with the postfrontal northeasterlies and results in an enhanced frontal convergence zone along the coast. To assess the effects of thermally driven circulations caused by the diurnal heating cycle on precipitation, we will study the rainfall characteristics during the diurnal cycle at different parts of the island. In addition, we will conduct a case study of local circulations over the island under the prefrontal southwest monsoon flow based on the data collected during IOP #11.