doi:  10.3878/j.issn.1006-9895.1901.18155
伊犁河谷“7.31”极端暴雨过程不稳定性及其触发机制研究

The Instability and its Trigger Mechanism of Extreme Precipitation Event in the Yili River Valley on 31 July 2016
摘要点击 166  全文点击 108  投稿时间:2018-04-26  
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基金:  国家自然科学基金项目41565003、41661144024,中央级公益性科研院所基本科研业务费专项资金项目IDM2016001
中文关键词:  伊犁河谷  暴雨  条件对称不稳定  触发机制
英文关键词:  Yili River valley  Rainstorm  Conditional symmetric instability  Trigger mechanism
              
作者中文名作者英文名单位
刘晶LIU Jing中国气象局乌鲁木齐沙漠气象研究所,乌鲁木齐830002;中亚大气科学研究中心,乌鲁木齐830002
周雅蔓ZHOU Yaman新疆气象台,乌鲁木齐830002
杨莲梅YANG Lianmei中国气象局乌鲁木齐沙漠气象研究所,乌鲁木齐830002;中亚大气科学研究中心,乌鲁木齐830002
曾勇ZENG Yong中国气象局乌鲁木齐沙漠气象研究所,乌鲁木齐830002;中亚大气科学研究中心,乌鲁木齐830002
刘雯LIU Wen中国气象局乌鲁木齐沙漠气象研究所,乌鲁木齐830002;中亚大气科学研究中心,乌鲁木齐830002
引用:刘晶,周雅蔓,杨莲梅,曾勇,刘雯.2019.伊犁河谷“7.31”极端暴雨过程不稳定性及其触发机制研究[J].大气科学,43(6):1204-1218,doi:10.3878/j.issn.1006-9895.1901.18155.
Citation:LIU Jing,ZHOU Yaman,YANG Lianmei,ZENG Yong,LIU Wen.2019.The Instability and its Trigger Mechanism of Extreme Precipitation Event in the Yili River Valley on 31 July 2016[J].Chinese Journal of Atmospheric Sciences (in Chinese),43(6):1204-1218,doi:10.3878/j.issn.1006-9895.1901.18155.
中文摘要:
      2016年7月31日至8月1日新疆伊犁河谷发生了一次极端强降水事件,多站突破降水极值。利用NCEP/NCAR 0.25°×0.25°再分析资料、中国地面卫星雷达三源融合逐小时降水产品及国家基本地面观测站逐时降水资料,通过天气研究和预报(WRF)数值模拟和诊断分析强降水期间大气的不稳定性及其触发机制,证实了不同尺度系统相互作用以及复杂地形的影响是干旱、半干旱地区极端暴雨形成的重要因子,并得出以下结论:(1)降水前河谷低层高对流有效位能积累,低层锋面东移触发对流有效位能释放,造成河谷第一阶段短时强降水天气;前期对流性降水释放湿对流不稳定能量,低层大气对称不稳定性逐渐增强,在对称不稳定作用下维持和加强了伊犁河谷第二阶段强降水天气。(2)第一强降水阶段期间大气低层为对流不稳定性层结,降水初期和第二阶段强降水期间大气均为条件对称不稳定性层结,对称不稳定的产生主要来自于湿位涡斜压分量(Mpv2),其中降水初期低层Mpv2变化由大气的湿斜压性和低层水平风的垂直切变所造成,第二阶段强降水低层Mpv2变化主要由大气湿斜压性造成。(3)第一阶段强降水期间,低层锋面和地形抬升,垂直运动迅速发展,造成河谷南、北部山前降水;河谷东侧中尺度气旋在地形阻挡下稳定少动,是东部地区短时强降水天气发生的直接启动机制。第二阶段强降水期间,中、低层锋区叠加爬坡,冷锋锋生,中、低层风场辐合区叠加,河谷东北部形成垂直环流圈,上升运动进一步发展,是造成河谷第二阶段暴雨的重要原因。
Abstract:
      An extreme precipitation event occurred from 31 July to 1 August 2016 in the Yili River valley during which multiple stations experienced off-the-charts precipitation values. Using the NCEP/NCAR 0.25° × 0.25° reanalysis data, the China Meteorological Administration (CMA) ground multi-source-merged hourly precipitation product, and hourly ground precipitation observation data, we performed numerical simulation and diagnostic analysis of the atmospheric instability and its trigger mechanism during heavy precipitation using the Weather Research and Forecasting (WRF) model. The results showed that the interaction of systems with different scales and the influence of complex terrains were important factors causing the extreme heavy rainfall in the arid and semi-arid areas. The results also revealed that the following: (1) During the first precipitation phase, the eastward lower cold front triggered the convective available potential energy in the lower convective unstable layer, which resulted in a short-term first heavy precipitation stage in the Yili River valley. After the unstable wet convective energy was released in the early stage of convective precipitation, the symmetrical instability of the lower atmosphere gradually increased, which maintained and strengthened the second heavy rainfall stage in the Yili River valley. (2) A lower convective instability layer was present during the first strong precipitation phase, which was a conditional symmetric instability mainly generated by the baroclinic component of moist potential vorticity (Mpv2 )during the initial precipitation period and the second strong precipitation period. Among them, the changes in Mpv2 at the lower layer during the early stages of precipitation were caused by the wet atmospheric baroclinicity and the vertical shear of the lower horizontal wind. The variability of the Mpv2 in the lower layer during the second heavy precipitation stage was mainly caused by the wet atmospheric baroclinicity. (3) During the first heavy precipitation phase, the lower frontal and topographical lifting led to the rapid development of vertical movement, which caused precipitation on the southern and northern slopes of the mountain in the Yili River valley. The mesoscale cyclone on the east side of the valley was stable and moved little due to the blocking effect of the terrain, which was a direct starting mechanism for the occurrence of the short-term rainfall in the eastern region. During the second stage of heavy precipitation, the convergence areas of the middle and lower wind fields were superimposed, and the high- and low-front areas were superimposed during the climbing process. The frontogenesis of the cold front caused vertical circulation in the northeast of the valley, from which the upward movement further developed and was a major cause of the second heavy rainfall stage.
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