大气运动非平衡强迫与“98·7”暴雨云团的中尺度特征  

MESO-SCALE CHARACTERISTICS OF THE UNBALANCED FORCE OF ATMOSPHERIC MOTION AND ENVIRONMENTAL FIELDS OF RAIN STORM ON 20—21 JULY 1998

作　　者：陈忠明[1] 闵文彬[1] 徐茂良[2] 高文良[1] 

机构地区：[1]成都高原气象研究所,成都610072 [2]成都大学都江堰分部,都江堰611830

出　　处：《气象学报》2004年第3期375-383,共9页Acta Meteorologica Sinica

基　　金：国家自然科学基金项目 ( 4 0 2 75 0 17) ;四川省青年科技基金项目

摘　　要：文中对 1 998年 7月 2 1日发生在武汉附近地区的突发性特大暴雨过程之激发机制与中尺度环境场特征进行诊断 ,结果显示 :(1 )引发本次突发性特大暴雨的 β中尺度对流云团 ,其环境物理场比较特殊 ,在暴雨最强时刻 ,对流层高低层没有独立的负、正涡度大值中心区与之对应 ,辐合层并不十分深厚 (低于 5 0 0hPa) ,且气流散合强度(1 0 -4s-1 )较旋转强度 (1 0 -5s-1 )大一个量级 (D ζ)。 (2 )在暴雨临发生前 ,对流层低层中尺度辐合增长较正涡度增长大一个量级 (Dt ζt) ;到暴雨最强时刻 ,尽管气流辐合已达到 1 0 -4s-1 量级 ,但涡度变化尚未适应到散度变化的水平。散度变化超前涡度变化与高空资料时间分辨率不足是暴雨最强时刻观测到D ζ的主要原因。 (3)在暴雨发生前 1 0余小时 ,大气运动已处于较强的非平衡状态 ,且越临近暴雨发生 ,U <0的非平衡性越强 ;而在暴雨最强时刻 (7月 2 1日 0 8时 ) ,大气运动即由U <0的非平衡态转为U≈ 0的准平衡态。 (4 )对流层低层大气运动非平衡动力强迫与 2 0The conventional and satellite data were collected and sorted by the Research Project Group of Cause and Prediction Application of 1998 Yangtze River and Nunjian River heavy rain. Besides conventional physical variables such as vorticity, divergence, vertical velocity θ se to represent the basic characteristics of atmospheric motion, We calculated thermodynamic parameter C D which reflects the sloppy development of vertical vorticity and the diagnostic variable U which reflects the unbalanced quality of mesoscale atmospheric motion and variability of vertical vorticity  ζ  t . Their calculation expressions are as follows:C D=ζ Sθ S/θ z=(-  v  z  θ  x+  u  z  θ  y)/(  θ  z)(1)U=-  2E+k·[  ×(f+ζ)V](2)  ζ  t=-(V·  )ζ-(f+ζ)  ·V-ω  ζ  p+  u  p  ω  y-  v  p  ω  x(3) Meso scale characteristics of environmental fields of rain storm and trigger mechanism of the abrupt heavy rain process occurred in Wuhan and its vicinal area from 20 to 22 July 1998 were analyzed. The result show that: (1) The heavy rain event was caused by a meso β scale convective cloud cluster. Environmental fields of rain storm were not related with strong cyclone vorticity or anticyclone vorticity center in lower or upper troposphere. Its divergence infensity was one order of magnitude higher than vorticity. (2) Closeing to occurrence of heavy rain, the increase of convergence was one order of magnitude higher than vorticity in the low layer of troposphere ( D  t  ζ  t ). The convergence intensity came up to 10 -4 s -1 at 08 AM on 21 July 1998 when heavy rain started, but vorticity didn't adjust to the intensity of divergence. The variation of divergence prior to vorticity and low resolution of observational data was the reason. (3) 10 hours before occurrence of heavy rain atmospheric motion was already unbalanced. T

关 键 词：大气运动 非平衡强迫 暴雨云团 中尺度系统 突发性暴雨 

分 类 号：P458.121.1[天文地球—大气科学及气象学]