一次入海气旋局地暴雪的结构演变及成因观测分析

Case study of the cause and the dynamic structure for a small-scale snowstorm event associated with a cyclone

中文关键词:  黄河气旋  暴雪  海效应  观测数据分析

英文关键词:Huanghe River cyclone  Snowstorm  Ocean-effect  Analysis of observation data

中文摘要:

      利用多普勒天气雷达、风廓线雷达、加密自动站、常规探空和地面等多种观测资料,对山东半岛东部地区一次局地暴雪过程的成因及动力结构演变特征进行了分析。结果表明:(1)此次局地暴雪过程分为两个阶段,第1阶段为典型的黄河气旋槽前降雪,降雪强度弱,雷达回波自西南向东北传播;第2阶段降雪为气旋后部的海效应降雪,降雪强度大,1 h降雪量可达到大雪量级,雷达回波自东北向西南移动,较为少见。(2)第1阶段降雪发生在对流层中层有明显低槽、低层有气旋性环流和西南低空急流及地面有气旋的天气系统配置下,水汽来源于中国南海,降雪落区位于高空槽前西南低空气流的右前方和地面气旋的东侧。(3)第2阶段降雪发生在高空槽过后,冷空气自渤海海峡和黄海北部入侵,降雪区域低层的主导风向为东北风,东北风强于西北风,降雪的水汽和热量来源于渤海海峡和黄海,雷达回波自东北向西南移动,降雪落区位于低层的东北风中。(4)海效应降雪各时段对流层低层风场结构不同。降雪初期,山东半岛北部沿海地面存在γ中尺度低压环流,雷达径向速度上表现为低层有β中尺度涡旋,东部沿海有东南风与西北风辐合;强降雪时段,边界层内存在东北风和西北风的切变线,低压环流和切变线是造成强降雪的有利动力条件。该个例揭示了发生在黄河气旋后部、由渤海海峡和黄海影响产生的山东半岛海效应降雪,其风场结构、雷达回波移向、降雪落区与风场的关系及降水相态等和常见的典型渤海海效应降雪有明显差异。

英文摘要:

      This study investigates the cause and the dynamic structure on a small-scale snowstorm event occurred in the Shandong peninsula with the Doppler radar, profile, automatic station, routine sounding and surface observation data. the results are as follows: (1) Precipitation occurred in the two stages: the first weak precipitation one was typical snowstorm caused by the Huanghe cyclone with the characteristic of weak snowfall and north-east radar echo, and the second strong precipitation one behind the cyclone was ocean-effect snowstorm with the characteristic of strong snowfall and south-west radar echo.(2) Favorable synoptic situation led to the occurrence of the first stage snow, such as the obvious trough, cyclonic circulation, southwestern low-level jet and surface cyclone. Its vapor came from the South China Sea. The snowfall was distributed to ahead of southwestern low-level jet on the right and eastern side of the surface cyclone. (3) By contrast, the second precipitation stage occurred after the trough passed the Shandong peninsula and the cyclone passed through the Bohai straight to the Huanghai Sea. Cold air intruded into the Shandong peninsula from the Bohai straight and the Huanghai Sea. North-east wind was prevailing and its speed was stronger than the north-west wind, which brought rich water vapor and heat. Snowfall distributed within north-east wind. And,(4) the structure of wind field in the lower troposphere was different during the ocean-effect snowstorm. At the beginning, there was a mid-γ scale low circulation beside the north coastal area in the Shandong peninsula, and radar radial velocity shows a meso-β vortex in low level. Meanwhile, there was a shear between the south-east wind and north-west wind near the east coastal area. During the strong snowfall, a shear between the north-east and north-west wind was found in the boundary layer. Both the low circulation and shear are the favorable dynamic factors. As a result, the case implies that remarkable difference between the Bohai strait/Huanghai Sea and the Bohai Sea ocean-effect snowstorm, the former is behind the Huanghe cyclone, and the latter is common and typical, in terms of the wind field structure, motion of radar echo and precipitation distribution.