台风尼伯特(1601)残留低压局地大暴雨成因分析

Effect of Residual Low of Typhoon Nepartak on a Local Extraordinary Rainstorm

利用常规观气象观测资料、地面自动站资料、NCEP/FNL逐6h的1°×1°再分析资料、多普勒天气雷达和风廓线雷达资料及GPS-PWV资料等,对江苏南通2016年7月11日一次大暴雨到特大暴雨过程进行了分析。结果表明:(1)该过程发生在台风尼伯特(1601号)残留低压、高空冷涡低槽和副热带高压共同作用的背景下;台风残留低压北侧倒槽顶部大的气旋性曲率和高空槽前减压导致低层苏南附近α中尺度低压生成,台风残留低压并入该低压,使低压发展,气压梯度加大,气压梯度力做功使动能增大,导致低空西南急流形成,利于暴雨发生;α中尺度低压内先后有D1、D2和D3等3个β中尺度低涡生成,其中D3造成了南通地区的大暴雨,中心位于南通大学附近,最大雨强达151.2mm·h^(-1)。(2)南通地区对流风暴触发后,降水的凝结潜热释放增强了对流风暴内的上升运动,促使低空中尺度偏东急流和其左前侧β中尺度低涡D3的形成和发展;之后,中层干冷空气入侵加强了对流不稳定和垂直风切变,使D3右侧多个低质心的γ中尺度单体风暴强烈发展且受低空风影响移动缓慢,强降水得以持续和跃增。(3)风垂直切变突增时间较强降水出现峰值时间早约30min,以及多普勒天气雷达径向速度的低空辐合(辐散)较对流风暴的发展(减弱)明显提前,对临近预报有一定的参考意义。

By means of the routine observations,surface AWS data,NCEP/FNL Operational Global Analysis data,Doppler weather radar data,wind profiler radar data and GPS-PWV data,we conduct an analysis of the extraordinary rainstorm in Jiangsu on 11 July 2016.The results indicate：（1）The residual low of Typhoon Nepartak,upper cold vortex and subtropical high were the advantageous synoptic background of this extraordinary rainstorm.The large cyclonic curvature at the top of the inverted trough and the pressure reduction of high trough caused a meso-α-scale low in South Jiangsu,merging with the residual low enhanced the pressure gradient,which resulted in the increase of kinetic energy,leading to the formation of a southwest low level jet（LLJ）,which is beneficial to the formation of the rainstorm.Three meso-β-scale vortexes（D1,D2 and D3）are formed successively in the meso-α-scale low,and the extraordinary rainstorm in Nantong developed with D3,with the center located around Nantong University,with the biggest rain intensity being 151.2 mm·h^（-1）.（2）The convective storm was triggered by the meso-α-scale low in Nantong,and the precipitation latent heat release enhanced the upward motion,which benefited the formation and development of the mesoscale easterly low level jet and meso-β-scale vortex D3 located in left.Meanwhile the middle-level cold-dry air intrusion enhanced convective instability and vertical wind shear,multiplied the low center-of-mass meso-γ-scale vortexes,continued to develop,and moved slowly,and then heavy precipitation continued and increased abruptly.（3）The sudden enhancement of the vertical wind shear appeared before the peak time of the rainstorm for 30 minutes early,and low-level velocity convergence（divergence）were obvious ahead of development（weakening）of the convective storm.The conclusions can provide valuable reference to nowcasting.