Journal of Arid Meteorology ›› 2020, Vol. 38 ›› Issue (4): 559-568.

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Analysis on Causes and Prediction Deviation of the “8·21” Heavy Rain in Northern and Central Part of Shaanxi Province

ZHAO Qiang, WANG Nan, CHEN Xiaoting, GAO Xingxing   

  1. (Shaanxi Meteorological Observatory, Xi’an 710014, China)

  • Online:2020-08-31 Published:2020-09-04

“8·21”陕西中北部暴雨成因对比及预报偏差分析

赵强,王楠, 陈小婷, 高星星   

  1. (陕西省气象台,陕西西安710014)
  • 作者简介:赵强(1981— ),男,高级工程师,主要从事灾害性天气预报技术研究. E-mail:zhaoq66@sina.com。
  • 基金资助:
    中国气象局预报员专项“关中‘8.21’对流暴雨成因及预报偏差分析”(CMAYBY2019-116)资助

Abstract: Based on conventional sounding observation data, ground encryption observation data and EC-interim reanalysis data with high resolution (0.25°×0.25°), the rainstorm process in northern and central part of Shaanxi Province during August 21-22, 2018 was comprehensively analyzed. The precipitation forecast based on the model was tested, and comparison of circulation conditions, water vapor conditions, energy conditions and instability mechanism of the heavy rainfall in the northern Shaanxi and the western part of the Guanzhong plain was focused on. The results show that cold air brought by the plateau trough and warm air brought by the subtropical high met in the central part of Shaanxi, which provided a favorable circulation background for the heavy rainfall. The shear line on 700 hPa provided a dynamic uplift condition for rainfall. The northwest cold front in the Hexi Corridor moved southward. The stable precipitation behind the cold front dominated in  the northern Shaanxi, while the convective precipitation triggered by the cold front dominated in Guanzhong area. During the rainstorm, the water vapor transport was weak, the local water vapor content was high, and the vertical gradient of humidity in western part of the Guanzhong plain was large, which was conducive to enhancement of convection and increase of rainfall intensity. Before the rainstorm, there were obvious convective instability in the middle and lower layers in western and central part of the Guanzhong plain and the convective effective potential energy (CAPE) was larger. Weak cold air triggered release of unstable energy in the Guanzhong plain and produced further convective rainstorm. However, there was a neutral stratification with weak unstable energy in northern Shaanxi. Conditionally symmetrical instability in the middle and lower layers resulted in strong oblique updraft, heavy rain and rainstorm. The frontogenesis of cold and warm air intersection in the Guanzhong plain was the triggering mechanism of convective rainstorm in this area. For large-scale precipitation, the forecast based on the model was stronger, but for convective precipitation, the  forecast  based on the model was weaker.


Key words: Key words: rainstorm, frontogenesis, atmospheric stability, trigger conditions, conditional symmetric instability

摘要: 运用常规高空观测资料、地面加密观测资料、EC-interim高分辨率(0.25°×0.25°)再分析资料对2018年8月21—22日(简称 “8·21”)陕西中北部暴雨过程进行综合分析,对模式的降水量预报进行检验,重点对比陕北和关中西部环流条件、水汽条件、能量条件、强降雨的不稳定机制等方面。结果表明:在陕西中部地区交汇的由高原槽带来的冷空气和副热带高压(简称“副高”)外围的暖空气,为暴雨提供了有利的环流背景,700 hPa切变线为降雨提供了动力抬升条件,受河西地区西北路冷锋南压,陕北以冷锋后部的稳定性降水为主,而关中为冷锋触发的对流降水。暴雨过程中水汽输送弱,本地水汽含量大,关中西部比湿垂直梯度大,有利于对流增强、雨强增大。暴雨发生前,关中西部中低层存在显著的对流不稳定,对流有效位能(CAPE)较大,弱冷空气触发关中不稳定能量释放,产生对流暴雨,而陕北为中性层结,不稳定能量弱,中低层有条件对称不稳定,其造成较强的斜升气流,产生大到暴雨。冷暖空气交汇在关中产生锋生,是该地区产生对流暴雨的触发机制。模式对于大尺度降水预报偏强,而对于对流降水预报偏弱。

关键词: 暴雨, 锋生, 大气稳定度, 触发条件, 条件对称不稳定

CLC Number: