“99.6”梅雨锋暴雨对流动量输送特征的诊断分析

DIAGNOSTIC ANALYSIS FOR CHARACTERS OF CONVECTIVE MOMENTUM TRANSPORT ON “99.6” MEIYU FRONT RAINSTORM

利用MM 5V3输出的高时空分辨率资料对“99.6”梅雨锋暴雨过程中对流动量输送特征X进行了诊断分析研究 ,主要结论如下 :( 1)模拟结果和观测分析的比较表明 ,中尺度模式MM 5V3能够成功地模拟“99.6”梅雨锋暴雨中尺度系统的发生和发展及演变。 ( 2 )通过对中尺度系统强烈发展时刻的对流动量输送 (CMT)诊断分析表明 :动量收支残差与平均流场的方向一致 ,它有利于加速西南气流北上 ,和 β中尺度系统的发生和发展 ;结果也表明强矢量几乎总是与产生强烈上升运动的 β中尺度系统相对应。动能转换的诊断表明 ,低涡前部的相间出现E >0和E<0的区域 ,这显示出在中尺度系统强烈发展时大尺度系统与中尺度系统之间的能量转换非常复杂 ,并不是简单的能量串级过程所能描述的 ;同时E的正值比负值的绝对值要大得多 ,这表明能量主要是从大尺度向次网格尺度转换 ,激发次网格尺度系统的发生和发展。 ( 3 )当切变线低涡离陆入海时 ,X矢量则对西南气流产生强烈的减速作用。 v和 vY的垂直剖面分析显示 ,南风此时在对流层中低层受到明显的减速作用。 ( 4 )转换能量E的垂直廓线显示 ,在中尺度系统强烈发展时 ,对流层中低层的能量顺尺度 (E >0 )输送非常强 ,而在低涡切变线离陆入海时 ,对流层则表现为逆尺度输送 (E <0 )。

The temporal and spatial high resolution data outputted from the Mesoscale Model (MM5V3) was used to diagnose convective momentum transport(CMT) on “99.6' Meiyu front rainstorm. The major conclusions as following:(1) The comparisons between results of simulated and observed shown, MM5V3 has the ability to replicate the large-scale and mesoscale circulations of the “99.6” Meiyu front rainstorm. (2)The diagnosis of CMT on the violently developing period of the mesoscale system show that the direction of momentum budget residual was consistent with the mean flow and acted to accelerate on the northward of southwest flow which favoring the genesis and development of the meso-β systems. It also shown that strong X always related to the meso-β systems. The distribution of kinetic energy transfer E suggested that the area of E>0 and E<0 were alternating during the intense development of mesoscale convective systems MCSs. It indicated that the energy transfer was more complicated between the large scale and subgrid systems and cannot be described as a simple energy cascade process. Overall, that positive value of E was much greater than the absolute negative E which suggested the energy was mainly transferred from the large-scale motion to subgrid scale eddies, hence induced the genesis and development of subgrid scale systems. (3) X strong deceleration on the southwest flow occurred when the low vortex with shear line move to the sea. The analysis of v and vY's cross sections indicates that the southerly was decelerated on low and middle levels of troposphere. (4) The vertical profile of E indicates that the strong downscale transfer of energy (E>0) mainly occurred in the middle and low levels of troposphere during the intense development of mesoscale systems and upscale transfer (E<0) occurred when the low vortex move to the sea.