【作者】 覃丹宇；

【导师】 方宗义； 江吉喜； 许健民；

【作者基本信息】 南京气象学院 ， 大气物理学与大气环境， 2004， 博士

【摘要】 本文从卫星气象的角度出发，利用卫星资料和NCEP／NCAR 1°×1°再分析资料，对梅雨暴雨云团的卫星观测及其形成和发展的机理进行了系列研究。先后分析了梅雨暴雨系统的云系成员及其相互作用；中尺度对流复合体（MCC）的结构、降雨特征、微物理特征及其形成和发展的有利环境条件；不同类型中尺度对流系统（MCS）形成与发展的环境条件差异；热带水汽羽和暴雨云团的关系，水汽羽的动力和热力特征。还借助位涡物理量及位涡观点、湿Q矢量及湿Q矢量散度对MCS进行诊断分析，并且利用MM5模拟了暴雨过程。 得到的主要结果如下： （1） 典型的梅雨暴雨系统的云系成员主要有四个，它们是：梅雨锋云系、西风带短波槽云系、青藏高原东移云系和季风云涌。这些云系成员都可以影响到梅雨锋云系的形状和强度，对梅雨锋云系的建立或重建都起到重要的作用。梅雨暴雨系统的云系成员是相应的天气系统相互作用的产物。副热带高压决定梅雨锋云系的位置，因此也决定了暴雨发生的区域。适当强度的高空槽可以诱生梅雨气旋，产生锋面气旋暴雨。高原东部云系如果受高原槽的引导可以移出高原，同时也诱生西南低涡并移出四川盆地，高空槽和低涡共同作用造成了沿途暴雨。南海和孟加拉湾的季风云涌在副高东退（或印度低压稳定加强）的时候，可以北上和梅雨锋云系连在一起，这同样也是产生暴雨的重要条件。 （2） 梅雨锋中的MCC内嵌有若干个中-β云团，对流体此生彼消十分活跃。随着云团最强对流的逐渐减弱，云团面积迅速膨胀，并持续数小时后很快减小。强降水主要发生在云团发展和成熟期中。强降水还与对流有关，降水强度总体上跟T_BB强度成正相关，T_BB越低降水越强。云顶相态显示MCC由多层云、卷云和密实冰云构成，在广阔的水云区里发展起来。降水强度最大的区域位于多层云附近，密实的冰云向水云过渡的冰云一侧。水凝物垂直分布显示，MCC中可降水冰含量最大，分布在几乎整个对流层，雨水和云水主要分布在的对流层中、低层，而云冰则分布于高层大气中。水凝物中心所在的位置对流活跃，对水凝物的升华或凝华过程起到促进作用。 （3） 卫星资料分析可以证实，利用夏大庆等人改进的Shuman—Shapiro滤波方法可以有效地分离出中尺度扰动。滤波后得到的中尺度系统与T_BB≤—52℃区域有较好的对应关系。滤波结果显示，MCS具有低空辐合高空辐散的扰动结构。中尺度气旋和中尺度切变线两种不同的中尺度组织方式，分别生成带状和近圆形的形态上差异很大的MCS。（4）（5）（6）（7）（8）有利于梅雨锋MCC发生、发展的天气形势为:西太平洋副高脊线维持在20oN附近，西端抵达华南西部;其南面的ITCZ和孟加拉湾季风云团很活跃。低空急流将暖湿空气输送到江淮地区，在30一35ON之间存在着一条切变线，其北部有500 hPa短波槽移过，上层200 hPa由于南亚高压东扩北抬，并形成一个辐散区。对流层中上部有季风水汽羽从孟加拉湾延伸到长江中下游地区，江淮切变线云系、高空短波槽云系和季风云涌的相互作用，是暴雨云团连续生成和发展的有利云型配置。MCC发生在较弱的斜压环境里，一般暴雨云团则发生在较强的斜压环境里。MCC作为较大型的中尺度对流系统，对低层高温高湿能量的需求比一般暴雨云团更多，因此要求高能舌范围更广、更深厚，与此相联系的位势不稳定区域也更大。不论是MCC还是一般暴雨云团，它们发生发展时水汽条件都很好，水汽通量猛增，水汽向北输送到达云团产生的地区，并且水汽强烈辐合。在较稳定的天气形势下，不稳定能量和水汽的积累主要由低空急流完成。MCC和一般暴雨云团都发生在低层切变线附近偏南的区域，这里有很强的正涡度，围绕切变线产生正的中尺度环流，即在切变线南部为低层辐合上升，北部为下沉辐散。研究发现，水汽羽和暴雨之间存在密切联系，水汽羽可能通过“播云”（cloud seeding）的效应来增强降水，或者说提高了降水的环境效率。在梅雨暴雨过程当中，水汽涌的北部边界大致与高空急流轴平行， MCS一般出现在300 hPa高空急流的右后方，距离急流轴约3个纬距的地方。高空急流的存在提供了很好的质量外流途径，即辐散机制，有利于Mcs的发展。在暴雨过程期间，水汽羽顶端内部维持有一条es。脊轴，走向和水汽羽平行，同时水汽羽也和一条正涡度带相对应，其位置和走向均和低空es。脊轴相吻合，体现了低层的动力抬升机制，正涡度中心基本和MCS相对应。典型的梅雨暴雨过程中对流层中上部的主要水汽型特征为，一条热带水汽羽从孟加拉湾经过青藏高原东部向东北方向延伸到江淮地区，并与中纬度水汽羽相互作用，MCS发生在热带水汽羽中。这条热带水汽羽是一条深厚的暖湿输送带，反映了中高层水汽从孟加拉湾向长江下游的输送，以及通过大尺度上升运动造成的水汽自下向上的垂直输送，并且与对流层上层的负涡度和正散度区域有很好的对应关系，具有低层辐合、高层辐散的大尺度垂直运动特征。热带水汽羽和对流层上部特定的大尺度环流型密切联系，并随着流场的变化而发生演变。水汽羽北部边界附近的暗带是一条与强涡度梯度和高?更多还原

【Abstract】 Using satellite data and NCEP/NCAR 1 1 reanalysis data, series of studies, from the viewpoint of satellite meteorology, are finished on mesoscale convective systems (MCS) and their possible genesis and evolution mechanism in the Meiyu front. These works include the cloud system families of the Meiyu heavy rainfall and their interactions, the structure, precipitation characteristics and microphysical features of the mesoscale convective complexes (MCC), the favorable genesis and evolution settings for MCS, the different environments between MCC and meso-p-scale convective system, the relationship between the tropical water vapor plume (WVP) and MCS, and what characteristics of the WVP. Also the scale-separated technique is introduced to depict the clear mesoscale structure with the MCS, and the isentropic potential vorticity (IPV) and the moist potential vorticity (MPV) are used to diagnose the evolution mechanism of MCS. Finally the powerful MM5 modeling system is run to help better understanding the initiation of MCS, as well as its dynamic and thermodynamic structures.Following are the investigations made in these studies and findings. The typical cloud system families of the Meiyu heavy rainfall are the Meiyu front cloudsystem, the westerly short wave trough cloud system, the cloud system from the eastern Tibetan plateau and the monsoon cloud clusters. Their interactions are important for the Meiyu cloud system’s construction/reconstruction to form a specific cloud style and intensity. The families are corresponded to synoptic systems, also are results of their interactions. In fact, the subtropical high affects the position of the Meiyu cloud system so that the region of heavy rainfall determined. The mid-level short wave trough could induce cyclone in the Meiyu front to produce associated heavy rainfall. When leading by the traveling short wave trough, the cloud system in the eastern Tibetan plateau could move eastward. Then the south-west cyclone follows from the Sichuan Basin to produce heavy rainfall on the way. Though the monsoon cloud clusters are not often to go across the east foot of the Tibetan plateau to the lower reaches of the Changjiang River Basin, they could touch the Meiyu cloud system whenever the subtropical high retreating eastward, hence heavy rainfall comes. The TBB (Black-Body Temperature) analysis depicts that several meso-p-scale cloud clustersand convective cells are embedded and alternately developed within a MCC. As the strongest convection gradually decrease, the cold TBB area expand quickly in hours before dissipation. However, the heavy rainfall occurs in MCC’s developing and maturing stages. And the minimum TBB fluctuation matches well to the precipitation trend (the lower TBB the heavier rainfall). The cloud top properties and cloud phase show that MCC develops in a broad water cloud area with multi-layer cloud, density ice cloud, and cirrus cloud consisted. The heaviest hourly rainfall orients to the density ice cloud portion where ice cloud become turn to be water cloud. The hydrometeors distribution in MCC illustrat that the precipitable ice is dominant which fills in the cloud cluster in almost entire troposphere with maximum cores at the mid-levels. Rain water and cloud liquid water are in the middle and lower troposphere, and cloud ice water only scatters at the 8-18km upper levels. The hydrometeor maxima extend over the location where the convection is most active, therefore hydrometeors transformation in condensation/sublimation processes are frequent. The satellite analysis confirms the MCS with certain mesoscale anomalies that revealed byscale-separated technique introduced by Xia Daqing (1983). The mesoscale systems have closed relationship to the - 52 TBB region with convergence in the lower levels however divergence in the upper levels. The different organizing of mesoscale cyclone and "convective line" makes the MCSs difference in shapes with circular or belt, respectively. A kind of favorable synoptic environment for Ma更多还原