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中文摘要：
2003年7月4～5日淮河流域发生了一次中尺度强暴雨过程，致使淮河洪水泛滥。这次暴雨过程由中尺度对流系统（MCS）以及因其发展而产生的低涡造成。通过对此次过程的诊断分析和新一代细网格WRF中尺度预报模式的数值模拟，研究了这次过程发生发展的机制。模拟结果较好地描述了本次暴雨及中尺度系统发生、发展的时空演变过程。分析结果表明：此次移动性暴雨过程的前期由不断向东移动发展的MCS造成，后期降水则由低涡切变线产生的中尺度低涡引起。同时，副热带高压明显偏西偏北，并维持较长时间，造成雨带一直维持在淮河流域。高层辐合中心的加强使低空急流不断增强，低空急流的增强进而引起低层辐合的加强，而低层辐合的加强以及上升运动的潜热释放导致低涡的发生，低涡形成及形成后移动缓慢，造成了淮河流域的大暴雨。高层中尺度辐散区的抽吸对低层中尺度涡旋的发生发展起到了促进和加强的作用。低层的中尺度辐合场和高层的中尺度辐散场的发展与耦合对中尺度系统的发展有很好的预示作用。低层中尺度辐合区的减弱预示着系统的衰减，西南偏西的中层相对干冷空气侵入并在梅雨锋前缘下沉促进了系统的衰减。
英文摘要：
A mesoscale torrential rain was observed in the Huaihe River valley from 4 to 5 July in 2003 that induced the flooding of the Huaihe River. The rainfall process was caused by a mesoscale convective system （MCS） and a vortex associated with its development. In order to study their mechanism of evolution, the diagnostic analysis of the rainfall process was performed, and the fine-meshed WRF mesoscale numerical model employed for the simulation analysis. The simulation results show that the rainfall and the genesis and development of the mesoscale system are well described. The analyses demonstrate that the precipitation in the early stage was brought about by an eastward moving and developing MCS, and in the later stage by a mesoscale vortex developed on the vortex-shear line. Meantime, the subtropical high laid significantly west and north of normal, and stayed there for a long time of period, causing the rain belt maintained over the Huaihe River valley. The strengthening of the upper-level convergence center led to the continuously intensifying of the low level jet stream, which in turn enhanced the lower-level convergence. The enhanced lower-level convergence and the release of the latent heat in the ascending motion resulted in the genesis of a vortex. Its genesis and afterwards slow movement brought about the torrential rain in the Huaihe River valley. The pumping of the upper-level mesoscale divergence area facilitated the genesis and development of the lower-level vortex. The development and coupling of the lower-level mesoscale convergence field and upper-level mesoscale divergence field is a good precursor of the development of the mesoscale system. The weakening of the lower-level mesoscale convergence indicated the decay of the MCS. Besides, the relatively dry and cold air in the middle troposphere entered the system from the west-southwest direction and then sank in the front of the meiyu front, which accelerated the weakening process of the MCS.
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