Synoptic and Mesoscale Analyses of Heavy Precipitation Events During TAMEX

小行星9421060 本计画将利用数值模式的结果及台湾地区中尺度试验（TAMEX）所收集的资料，研究TAMEX期间有利于强降水发展的天气尺度、中尺度及局地过程。 当梅雨锋接近台湾岛时，锋前西南季候风气流（或低空急流）从南方带来暖湿的不稳定空气。 除了低层抬升（地形和锋），高层强迫（与分流气流相关的高层辐散或与急流锋系统相关的锋生强迫）的存在是副热带大范围暴雨发展的必要条件。 在这项研究中，我们将诊断LLJ模型生成的高分辨率数据的基础上。 特别是，气旋生成和LLJ的发展之间的联系将进一步研究。 此外，我们将研究导致广泛降水发展的高、低空环流之间的耦合。 天气尺度环流控制着是否会发生大范围降水，而中尺度环流、局地环流和地形效应则控制着对流发生的确切时间和地点。 我们将利用雷达、飞机和常规资料，结合嵌套网格模式，研究台湾地区的锋前中尺度气流。 特别是，我们将集中在迎风面的气流，因为高层槽/低空急流接近。 在锋前西南气流中，偏南急流沿着海岸偏转，形成有利于深对流发展的局部辐合带。 当锋面移到台湾北方上空时，偏南气流可能在台湾海峡西北沿岸与未偏南的西南气流汇合，形成有利于深对流发展的局部辐合带。 当锋面移经台湾北方时，偏南气流可能与锋后东北风汇合，并导致沿海岸沿着锋面辐合区增强。 为了评估由日加热循环引起的热力驱动环流对降水的影响，我们将研究该岛不同地区日循环期间的降水特征。 此外，我们将根据IOP#11期间收集的资料，对台湾在锋前西南季风气流下的局地环流进行一个个例研究。

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.