陆水交界区域对线状中尺度对流系统强度的影响—以杭州湾为例

The mesoscale convective systems (MCSs) crossing from land to water always cause disastrous severe convective weather like strong thunderstorm wind, short-time severe precipitation, etc. Due to the lack of systematic understanding the characteristics of strength variations and the main influencing factors, the strength variations of linear MCSs entering the water are very difficult to be predicted accurately. In this project, the Hangzhou Bay is chosen as research region and the cases of linear MCSs entering the Hangzhou Bay during the recent 10 years are selected. Then the characteristics of strength variations are statistically analyzed. Besides, the ambient conditions of these cases are analyzed by using the pattern identification method and the severe weather analysis method, and then the typical synoptic patterns and environmental parameters are worked out, which help to identify the increased and decreased categories. Using the Variational Doppler Radar Analysis System (VDRAS), the effects of dynamical and thermodynamical factors over the land-water boundary region to the convections over the Hangzhou Bay is studied. Furthermore, high-resolution mesoscale numerical model is utilized to simulate typical cases and do sensitivity tests, and how the Hangzhou Bay impacts the strength of MCSs when they entering the Hangzhou Bay is investigated. The successful implementing of this project will help to increase the understanding of the characteristics of strength variation and their main influential factors for the coastal linear MCSs when they entering the Hangzhou Bay, and provide scientific references for improving the forecasting accuracy and warning capability of severe convective weathers in the land-water boundary regions in China.

从陆地移入水体后增强的线状中尺度对流系统常引发雷暴大风、短时强降水等灾害性强对流天气。由于对水上线状中尺度对流系统的强度变化特征和主要影响因子缺乏系统认识，目前仍是业务预报工作中的难点。本项目拟以杭州湾为例，挑选近10年移入杭州湾的线状中尺度对流系统，统计分析其强度变化特征；利用流型识别法和基于构成要素的强天气分析法分析入海线状中尺度对流系统的环境条件，初步区分增强类和减弱类的特征流型配置和环境参数；利用VDRAS同化分析系统，研究典型个例中杭州湾陆水两侧的中小尺度热力和动力条件对入海对流海上部分的局地影响；进一步利用高分辨率中尺度数值模式对典型个例进行数值模拟和敏感性试验，研究杭州湾对线状中尺度对流系统入海强度所起的作用。项目研究结果将有助于系统认识我国杭州湾地区入海线状中尺度对流系统的强度变化特征和主要影响因子，并为提高我国陆水交界区域强对流天气的预报准确率和预警能力提供参考依据。

从陆地移入水体后增强的线状中尺度对流系统常引发雷暴大风、短时强降水等灾害性强对流天气。由于对水上线状中尺度对流系统的强度变化特征和主要影响因子缺乏系统认识，目前仍是业务预报工作中的难点。. 本项目以杭州湾为例开展研究。根据判据，挑选出2006-2019年3月-9月移入杭州湾的线状中尺度对流系统共30个，其中14个是加强的，16个减弱。统计表明，6-9月发生的入海个例较多，而一天中13时到19时入海个例较多，尤其是集中在16-18时。. 利用流型识别法和基于构成要素的强天气分析法，对30个个例发生时的高低空配置及对流参数进行了详细分析。通过统计分析和对比研究，发现增强类的CAPE与减弱类的CAPE差异不大。这说明在预报对流入海后是增强还是减弱，CAPE并不是一个很好的判别指标。而增强类的垂直风切变明显大于减弱类，因此垂直风切变是一个非常好的判别入海强度变化的指标。从中位数来看，增强类从入海前6小时到入海时刻，垂直风切变不断增强。在能量条件满足的条件下，0-3km垂直风切变超过10m/s，0-6km垂直风切变超过14m/s，移入杭州湾的线状对流系统增强的概率非常大。. 利用VDRAS同化分析系统，研究2014年7月27日移入杭州湾飑线过程的形成和发展机制。基于VDRAS得到的对流分辨率资料开展研究发现，吹向杭州湾西海岸的海风（偏东风）与自西向东移动的雷暴出流（偏西风）相遇对于海岸线附近对流的发展加强起到了重要作用。研究还发现，Weisman提出的弓形回波生成模型对于此次海上弓形回波的形成同样适用，即后侧入流急流下沉到地面，造成了弓形回波及近地面大风。. 项目研究结果将有助于系统认识我国杭州湾地区入海线状中尺度对流系统的强度变化特征和主要影响因子，并为提高我国陆水交界区域强对流天气的预报准确率和预警能力提供参考依据。该项目所用的研究方法也可以借鉴到其他海域的研究。