利用加密探测资料分析冷式切变线类大暴雨的动力结构

利用风廓线雷达、多普勒天气雷达、地面加密自动站和闪电定位仪等非常规观测资料,对发生在山东东南部沿海青岛的一次大暴雨天气的动力结构进行了分析,以探索如何综合应用新资料追踪暴雨的演变过程。结果表明:(1)此次大暴雨过程的影响系统是冷式切变线,冷空气从对流层低层入侵,切变线在850 hPa以下层次明显,地面冷锋逐渐演变为静止锋。(2)暴雨过程经历了两个强降雨和一个弱降雨时段,1小时30 mm以上的短历时强降雨发生在冷空气刚入侵阶段,并伴随雷电。(3)强降雨主要发生在925 hPa切变线附近,降雨分布在925 hPa切变线的东北风与850 hPa切变线的西南风叠置区域。大暴雨的分布与切变线走向基本一致。(4)在切变线移动和发展过程中,水平风有明显不同:冷空气刚影响时,对流层低层产生了明显的中尺度低压环流,是导致对流性短历时强降雨的关键因素;静止锋形成的时段内,从低层至高层,低压环流消失,代之以较强西南风与弱西北风之间的切变线;在静止锋维持的后期,低层和高层均转为西北风,仅在中层有西南风与偏北风之间的切变线,从而产生稳定性弱降雨。(5)风廓线对降雨的起止、盛衰有较强信号,风向风速自上而下顺序变化,当中层西南风风速增大且不断向下扩展,持续4 h后西南低空急流明显加强,当近地面转为东北风时,强降雨开始,强降雨阶段的显著特点是在风廓线雷达上表现为中低层强西北风和强西南风交替出现,降雨强度与交替的高度有关;当各层均转为稳定的西北风时预示降雨结束。

Analysis on Dynamic Structure of Cold Wind Shear Heavy Rainstorm by Intensified Observational Data

With observational data from wind profiler, Doppler weather radar, surface automatic weather station (AWS) and lightning position finder, the dynamic structure of a heavy rainstorm is analyzed to search how to follow a rainstorm case by kinds of new data. This case occurred in Qingdao, the coastal city in the southeast of Shandong Province. The results are as the following. Cold wind shear is the prevailing weather system to cause the rainstorm. Cold air comes first from the lower troposphere and then cold front becomes stationary. Wind shear is obvious below 850 hPa.There are three rainfall phases. The heaviest rainfalls with strong lightning produced when cold air bursts near wind shear in 925 hPa. Rainfall was distributed in the over lapping area between northeast wind at 925 hPa and southwest wind at 850 hPa. Heavy rainfall is in accord with wind shear. Horizontal wind is obviously different during the wind shear developing. Mesoscale cyclonical circulation that is the key factor to produce convective heavy rainfall is remarkable at the beginning of cold air bursts. But it disappeared and is replaced by the wind shear at the forming of stationary front. In the end of stationary front, the wind shear only preserves in the mid troposphere so that stable and weak rainfall can be seen. Wind profiler data are good signal for rainstorm development. Rainfall begins with southwest wind strengthening 4 hours later and wind direction turns northeast near the surface. Strong north and south winds change by turn, which is the significant features of the heavy rain. Rain ends when wind turns north in every altitude.