• CN 62-1175/P
• ISSN 1006-7639

### Causes Analysis of a Heavy Rainfall Associated with Typhoon and Forecast Difficulties in Northeastern Zhejiang

1. Ningbo Meteorological Observatory of Zhejiang Province, Ningbo 315012, Zhejiang, China
• Online:2018-04-30 Published:2018-04-30

### 一次与台风相关联的浙江东北部暴雨成因及预报难点分析

1. 浙江省宁波市气象台，浙江宁波315012
• 通讯作者: 钱燕珍，从事灾害性天气等预报技术研究. E-mail:qian-y-z@163.com。
• 作者简介:陈有利，男，主要从事天气预报及服务研究. E-mail:Ccyll99@163.com。
• 基金资助:

浙江省宁波市科技局项目（2014C50024和2015F1020）、浙江省气象局预报员专项项目（2017YBY03）及宁波市气象局青年项目（NBQX2017002C）共同资助

Abstract:

The heavy rainfall occurred in northeastern Zhejiang Province during the activity of typhoon Khanun in the South China Sea. The duration of rainfall and the moving path of heavy rainfall zone were difficulties in forecast of the rainfall process. Based on the conventional and intensive observational data, cloudy images of satellite and NCEP re-analysis data, the forecast difficulties of the heavy rainfall and its causes were analyzed synthetically in northeastern Zhejiang Province. The results showed that the extraordinary rainfall happened mainly in two stages in northeastern Zhejiang due to the activity of typhoon Khanun. During the first stage, the inverted trough formed over northeastern Zhejiang due to the cold air invading into the north side of the typhoon, which made confluence of the northeastern and southeastern air flow over northeastern Zhejiang, and then the convergence strengthened obviously, which caused the rainfall. As the typhoon Khanun moved westward, the rainfall zone moved westward. The heavy rainfall in the second stage was caused by the development of low-level cyclonic circulation, convergence in low level and strong input of water vapor. The strong rainfall zone moved northeast with the moving northeast of cyclonic circulation. The income of water vapor and its increase or decrease in low-level were 6 to 12 hours earlier than the generating of rainfall and its strengthening or weakening. The water vapor flux on 850 hPa was above 25 g·hPa-1·cm-1·s-1 and the water vapor flux divergence was below -20 g·hPa-1·cm-2·s-1, which was 6 to 12 hours earlier than the heavy rainfall. Coupled with the large positive vertical helicity, the fluid rotation was strong and the vorticity input into the convection system, which was 6 hours earlier than the appearing of the strong rainfall over northeastern Zhejiang. In addition, the negative value of Q* divergence was 6 to 12 hours in advance of the heavy rainfall.

1720号台风“卡努”在南海活动期间，浙江东北部地区出现暴雨，降雨持续时间和强降雨带移动轨迹是本次暴雨预报的难点。利用常规观测和自动站加密观测资料、卫星云图资料及NCEP再分析资料，综合诊断分析了此次暴雨过程的成因和预报难点。结论如下：本次浙江东北部降雨过程分14日08:00至15日13:00和15日14:00至17日08:00两个阶段，第一阶段是“卡努”台风倒槽顶部东南气流和东北气流汇合，以及弱冷空气参与影响造成的降雨，随着“卡努”的西移，雨区随之西移；第二阶段是低层低压环流发展，且低层有强的水汽输入和辐合造成的暴雨，强降雨区随着低压系统一起东北移。低层水汽收入及其增减，对于降雨的开始及增强或减弱有6～12 h的提前。850 hPa水汽通量值在25 g·hPa-1·cm-1·s-1以上，水汽通量散度值在-20 g·hPa-1·cm-2·s-1以下，对应区域接下来的6～12 h有强降雨。垂直螺旋度正值比较大，对应的浙江东北部地区有很强的流体旋转，且对流系统中有涡度输入，该地区之后6 h将出现强降雨。Q*散度负值对强降雨有6～12 h的提前预示。

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