甘肃一次区域性大暴雨分析

Analysis on a Regional Rainstorm in Gansu Province

利用甘肃省甘谷县气象观测站资料、NCEP/NCAR 1°×1°再分析资料、FY-2C卫星云图及天水多普勒C波段雷达资料,对2006年8月27日甘肃区域性大暴雨过程进行了分析。结果表明:①此次暴雨主要是西太平洋副热带高压西伸北抬配合西北弱冷空气的扰动造成的,是西北地区一次典型的暴雨形势;②暴雨大值区垂直环流发展明显,辐合上升运动发生在地形迎风坡的半山腰,地形的抬升作用在此次强降水过程中起重要作用;③多普勒雷达导出产品垂直液态水含量在此次暴雨过程中有很好的对应关系。在对流降水过程中,当不稳定能量达到最强的时候降水开始,而垂直速度达到最大、水汽通量发展到最强的时候,降水量最大,地面水平风速为零,也是降水量达到最大的表现。

In this paper, a rainstorm occurred in Gansu Province on August 27, 2006 is analyzed using the daily data observed by Gangu Meteorological Station in Gansu Province, NCEP/NCAR 1° × 1 ° reanalysis data, infrared satellite nephograms observed by FY-2C and C wave band data observed with Doppler radar at Tianshui. The results are as follows ： （ 1 ） The rainstorm was caused by the westward and northward advance of the Pacific subtropical high and the weak disturbance of northwest cold air, it was a typical rainstorm in northwest China, and also a primary circumfluence situation of local rainstorm in Gansu Province ; （2） Southeast Gansu Province is a large area of vapor flux convergence, the South China Sea and the Bengal Bay are the main source regions of vapor. In the rainfall process, vapor was incessantly transported to the rainfall region, and the unstable warm and humid air mass was increased; （3） The lower-level convergence, upper-level divergence and vertical ascent motion provided probably the suitable dynamic environment for the generation and development of the rainfall system ; strong convergence of vapor flux and the conditional convective instability in the lower troposphere provided probably the suitable thermodynamic environment for the generation and development of the rainfall system; （4） In the rainfall process, vertical circulation developed obviously, and the convergence ascending motion occurred at the windward slope of the terrain hillside. As a consequence, the terrain played an important role in the heavy rainfall.