宁夏西吉两次诱发地质灾害的极值暴雨对比分析

摘要

Using NCEP/NCAR re-analyzing data at 1 ×1°resolution and general observational data,compara-tive analysis of changing characteristics of environmental field conditions of extreme rainstorms inducing geologic haz-ards in Xiji at June 20,2013and June 18,2014 is carried out.Analysis discovered that:the two processes are all caused by plateau depression system,wind shear and low-level jet,and is closely related to the subtropical high ac-tivity and stable circulation background,when “20130620 process”occurs,there is typhoon activated in the Western Pacific Ocean,and the subtropical high moved to northeast and is northeast and southwest oriented,the “askew neck”high pressure at the Hetao area made the cold and warm air continuous intersection in the central and southern regions of Ningxia;While when “20140618 process”occurs,no typhoon is activated and the subtropical high is quasi east and west oriented,and moved to south,and the weak anti cyclone circulation in the north of Ningxia made the cold and warm air intersection in southern regions of Ningxia.Before the two process occurs,there are all moisture convergence in the low level、energy accumulation and uplifting at the whole level,As “20130620 process”,the low-level moisture convergence is strong ,moisture content in whole layer and unstable energy is large but the variable amplitude is small,the wind speed decreases with height and the vertical shear is small,maximum hourly rainfall in-tensity is small but continued for a long time;As for “20140618 process”the low-level moisture convergence is weak ,but the middle and up layer divergence is strong,while the variable amplitude of the whole layer moisture content and unstable energy is small,the wind speed increase with height and the vertical shear is strong,maximum hourly rainfall intensity is large but continued for a short time.%利用 NCEP 1°×1°再分析资料和常规观测资料，对2013年6月20日和2014年6月18日西吉两次极值暴雨环流背景和形成条件进行对比分析，发现这两次暴雨均与稳定的环流背景和副热带高压活动有关，由青藏高原移出冷性低值系统和风向风速切变及低空急流影响所致。“20130620过程”西太平洋洋面有台风活动，发生在副热带高压西伸北抬期间，河套“歪脖子”高压使冷暖空气持续交汇于宁夏中南部地区；而“20140618过程”无台风活动，发生在副热带高压南退期间，河套弱反气旋环流使冷暖空气交汇于宁夏南部。过程发生前低层均有水汽辐合、能量积聚过程和整层抬升运动，“20130620过程”低层水汽辐合强、整层水汽含量和不稳定能量大但变幅小，风速随高度减小且垂直切变小，最大小时雨强小但持续时间长；“20140618过程”低层水汽辐合较弱但中高层辐散抽吸作用强，整层水汽含量拉升快变幅大，不稳定能量降幅小，风速随高度增大且垂直切变大，最大小时雨强大但持续时间短。