中文摘要：

利用中尺度η坐标模式对1998年7月21～22日鄂东特大暴雨过程进行了数值模拟,通过地形敏感性试验,分析了地形对鞍型场和低空急流的影响,概括了鄂东地区β中尺度低涡及特大暴雨形成的概念模型。结果表明,在全地形的情况下,降水和实况接近,700 hPa鞍型场稳定维持,鞍型场位置和实况接近,鄂东地区的β中尺度低涡形成于鞍型场中性点附近;而无地形试验模拟降水量偏小、降水开始时间偏迟,河套地区高压和西南涡偏北,造成700 hPa鞍型场偏北,鄂东地区无法形成β中尺度低涡。青藏高原地形对其北部及南部气流的阻滞、绕流作用以及侧边界的摩擦作用对河套地区高压和西南涡的形成和维持有重要作用。积分时间越长,地形的作用越明显。在全地形试验中,汉口南侧中尺度低空西南风急流的加强是β中尺度低涡形成的重要因素,当加强的西南中尺度急流传播到（或形成于）鞍型场中性点附近时,其左侧容易形成β中尺度低涡,并在合适的热力条件下得到发展。

英文摘要：

The extremely heavy rain（EHR） in the east of Hubei Province（EHBP） during 21~22 July 1998 is numerically simulated using a regional mesoscale η-coordinate model.By terrain sensitivity experiments,the effects of terrain on 700 hPa saddle pattern and low-level jet are analyzed,and the conceptual model of the formation of meso-β scale low vortex（MSLV） and EHR is summed up.It is shown that in the case of whole-terrain,the simulated precipitation is similar to that of observation,the 700 hPa saddle pattern maintains stably,the location of the saddle field is close to that of observation,and the MSLV in EHBP forms near the neutral point of the saddle field.In the case of non-terrain,the simulated precipitation is too small,and it starts relatively late,the Hetao high and the southwest vortex locate to the north of which in the whole-terrain experiment,then it cause the same result for the 700 hPa saddle pattern,so the MSLV can not form in EHBP.The block,rounding effects and the lateral boundary friction of the Tibetan Plateau topography on the northern and southern airflow play an important role in the formation process and maintenance of the Hetao high and the southwest vortex,the longer integration time,the more obvious the role of the terrain.In the whole-terrain experiment,the enhancement of the intensity of the southwest low-level mesoscale jet（LLMJ） at the south side of Hankou is an important factor for the formation of MSLV.When the strengthened southwest LLMJ spreads to（or forms at） a location near the neutral point of the saddle field,the MSLV may form easily at the left side of southwest LLMJ,and may develop under suitable thermal conditions.