浙东地形对台风“利奇马”极端降水的影响分析

Analysis of the effects of the topography of eastern Zhejiang on the extreme precipitation of typhoon“Lekima”

利用自动站实时降水资料、NCEP再分析资料和多普勒雷达资料,结合中尺度数值模式WRF对台风“利奇马”在浙东地区产生的极端降水过程进行分析,重点研究了浙东地形对极端降水的影响。结果表明,“利奇马”影响期间,浙东强降水过程出现2个雨量峰值,依次由台风外层螺旋云带和台风中心附近的多个中尺度对流云团持续影响所造成,浙东地形对这一系列对流云团有明显的加强作用。浙东地区西部山脉对“利奇马”有阻滞和辐合抬升两方面作用,前者通过地形阻挡拖曳,延长强降水时长,后者通过山前显著的动力抬升作用和水汽辐合加强造成降水增幅。根据估算可知,括苍山脉在强降水阶段对暴雨的增幅可达11 mm·h^(-1),接近此时段内总雨量的2.5成。通过敏感性试验降低地形高度后,浙东地区辐合及上升运动减弱,雨量也明显减少,进一步验证了浙东地形是造成此次极端降水事件的重要原因。

Combined with the mesoscale numerical model WRF,the automatic station precipitation data,NCEP reanalysis data and Doppler radar data,were used to analyze the extreme precipitation process in eastern Zhejiang of typhoon“Lekima”.Moreover,the effects of topographyon the extreme precipitation in eastern Zhejiang were mainly studied.Results show that two rainfall peaks occur during the strong precipitation period of“Lekima”in eastern Zhejiang,which are caused by the continuous influence of several mesoscale convective clouds in the outer spiral cloud belt and the neartyphoon center.The topography of eastern Zhejiang has a significant strengthening effect on the series of convective clouds.The western mountain in eastern Zhejiang has two functions of blockage and convergence uplifting.The former in extends the duration of strong precipitation dragged by terrain,while the latter strengthens the precipitation through the remarkable power uplift and water-vapor convergence in front of the mountain.According to the estimation,the increasing of precipitation of Kuocangshan Mountains during the strong precipitation period can reach to 11 mm·h^(-1),close to 25%of the total rainfall during this period.In addition,after reducing the terrain height by sensitivity experiments,the convergence and uplifting motion in eastern Zhejiang region weakens,and the rainfall is also significantly reduced,which further verifies that the topography of eastern Zhejiang is an important factor of this extreme precipitation event.