“强降水和黄海气旋”中的干侵入分析

Analysis on Dry Intrusion in Heavy Rain and Huang-Hai Cyclone

利用GOES-9卫星6.7μm的水汽图像资料、等熵气流、位涡(IPV,MPV1)、sθe等物理量,对2003年梅雨期的一次强降水过程进行了分析,以揭示干侵入在强降水和黄海气旋中的作用。分析结果表明:(1)水汽图像暗区动态对强降水、温带气旋发展有很好的预报指示意义。(2)叠加了相对湿度场的垂直气流的发展、变化特征能清楚地反映干侵入与强降水的关系,对短时预报有一定指示意义,干侵入对强降水起激发作用。中层以上的干区与水汽图像暗区十分吻合。(3)sθe=340K等熵面上的气流能较好地反映对流层中上部的干侵入特征,sθe=330K等熵面上的气流能较好地反映黄海气旋发展特征。沿等熵面高脊区的下滑急流与水汽图像暗区相当一致。IPV大值区的发展变化与气旋快速生成、发展关系较好,IPV分布能较好地反映干侵入特征。(4)等压面上的MPV1空间、时空剖面均能很好地描述干侵入的演变特征。当MPV1≥0.4 PVU的区域向下伸展时,在其以南约2个纬距处出现强降水。(5)对气旋附近的强降水,干侵入起逐渐加强作用;对远离气旋区域,MPV1大值区域与强降水突然出现几乎是同步的,说明MPV1所反映的干侵入特征对强降水的作用在气旋附近与远离气旋区有所不同。强降水出现在sθe陡峭和密集区中。

Using the water vapor （WV） image, isentropic flow, potential vorticity（isentropic potential vorticity, moisture potential vorticity） and θse, a heavy rain process during Meiyu period is analyzed to reveal the effect of dry intrusion on heavy rainfall and Huang-Hai cyclone. The main results are as follows： （1） Dark zone in WV image is a good predictor for heavy rain and extratropical cyclone. （2） The development and change of vertical flow overlapped with relative humidity can clearly reflect the relationship between dry intrusion and heavy rain. It is a good predictor for very snort-range iorecasting. Dry intrusion , triggers the heavy rain and the dry zone above middle-level corresponds well with dark zone in WV image. （3） The airflow on 340K and 330K isentropic surfaces indicates the characteristics of dry intrusion in the middle- and top- of troposphere and Huang-Hai cyclone, respectively. The jet sliding along the ridge on isentropic surface is consistent with the dark zone in WV image. The big value of IPV relates well with the initiation and development of cyclone. It＇s distribution provides the features of dry intrusion. （4） The temporal and special cross-section of MPV1 on isobaric surface can reflect tne evotution of dry intrusion. Heavy rain occurs in the southern 2-- latitude when the area of MPV1 greater than 0.4 PVU extends downwards. （5） Dry intrusion can strengthen the rainfall near the cyclone. It is almost the same time for the happening of the heavy rain and the big value of MPV1. This indicates that the effect of dry intrusion on the heavy rain near and far from cyclone is different. Heavy rain often appear in the area of sharp and dense θse.