淮河流域大别山地形对梅雨期暴雨低涡影响的模拟研究

Simulation study on effects of terrain of Dabie Mountains on rainstorm cyclone in Huaihe River Basin during Meiyu period

基于淮河流域梅雨期低涡暴雨落区及低涡移动路径的统计特征,设计WRF数值模拟方案,研究大别山脉对浅薄低涡及其暴雨的地形强迫机制。结果表明:1)在三组数值试验中,无山脉时低涡东移速度较快,北绕山脉路径较慢,翻越山脉的移速居中;无大别山地形时,低涡路径明显偏南,显示低涡具有沿低地移动的特征;大别山地形倒置时,大尺度山体的出现迫使低涡北绕,路径更偏北。2)低涡反气旋式北绕,抵消和减弱了低涡强度;无山脉时,低涡强度由自身系统维持,强于北绕低涡;翻越山脊的低涡经历位涡守恒过程,山后强度几乎成倍增强。3)山脉梯度大,其强迫抬升作用大于低涡系统性抬升,两者叠加造成垂直上升速度增强近1倍。4)山后总涡度增强主要表现为低层涡度平流项、扭转项和散度项的明显增强,其增量可达1倍,但中层因子的影响不显著。5)强降水雨带发生在低涡偏东气流和偏南急流的汇合处,表明淮河流域暴雨低涡北部为强降水预警区。6)山脉通过对低涡东移路径的强迫,进一步影响暴雨强降水带的南北偏移。

Based on the statistical characteristics of rainstorm location and trajectory of the cyclone in the Huaihe River Basin during Meiyu period,the schemes of WRF numerical simulation are designed and the purpose is to investigate the orographic forcing mechanism of terrain of Dabie Mountains on the shallow rainstorm cyclone.Results show that:1)In the three simulation experiments,the eastward speed of cyclone is the fastest in the experiment without terrain of Dabie Mountains,the slowest for the cyclone going around northern mountains,and the medium for the cyclone passing over mountains.Without terrain of Dabie Mountains,the trajectory of the cyclone is obviously in the south of the trajectory of cyclone going around northern mountains,showing that the cyclone has a feature of moving along lowland.With inverted terrain of Dabie Mountains,affected by the large scale mountain,the cyclone is forced to go around northern mountains,with a more north trajectory than those of the cyclone passing over mountain and the cyclone in experiment without terrain of Dabie Mountains.2)The effect of mountain on cyclone intensity is that it can offset and reduce the intensity when the cyclone going around northern mountains with an anticyclonic trajectory.In the experiment without terrain of Dabie Mountains,the cyclone maintains its intensity by self system and is stronger than the cyclone going around northern mountains.When the cyclone has passed over the ridge of mountain,it has a double intensity,because the cyclone experienced a potential vorticity conservation process in front of and behind the ridge.3)The forced ascending motion of mountain with a large gradient is larger than the systematic uplift of cyclone.The vertical upward velocity with both mountain forcing and cyclonic convergence can increase nearly one times.4)The enhancing of total vorticity behind the ridge of mountain mainly shows that the low level vorticity advection,twisting and divergence terms have marked increase,and their increments can reach up to one times,but the changes of the terms are small in the middle level.5)The strong rainfall usually happens in the north part of cyclone where the south jet met the east flow of the cyclone,indicating that a warning area of strong rainfall locates in the north part of rainstorm cyclone in the Huaihe River Basin.6)By the topographic forcing on eastward trajectory of cyclone,the mountains can further influence the north south location of rainstorm zone.