基于GPM与ERA5数据的北太平洋冬季风暴路径降水个例分析

A case study of precipitation along the winter storm track in the North Pacific based on the GPM and ERA5 data

北太平洋风暴路径对全球气候有重要影响,研究北太平洋风暴路径区域降水结构有助于更好地理解风暴路径对全球大气的水汽和热量输送作用。本文利用全球测雨卫星(GPM)数据与欧洲中期天气预报中心(ECWMF)第五代再分析资料(ERA5),以2014年12月20-24日发生在北太平洋风暴路径区域的一次温带气旋过程为例,选取该气旋带来的3个降水片段,分析其降水结构和云参数结构特征。结果表明:3个降水片段的环流背景场相似,其水汽分布存在南北差异,造成水汽通量散度分布不同,致使各片段降水强弱不一,降水均集中在气旋中心的东南侧;通过对比温带气旋中降水强度和水汽含量的关系发现,更多可降水量并不一定带来更大降水强度,但气柱中水汽含量决定降水强度的上限。3个降水片段的反射率因子垂直剖面上均存在明显的冰水转换层,但各片段冰水转换层分布存在差异。由双频测雨雷达(DPR)得到的3个降水片段的粒子谱可知,各片段有效粒子半径强度分布与反射率因子强度分布具有较好的一致性,而粒子数浓度则与其他两者并不一致,其中的机理仍有待研究。基于GPM与ERA5的融合数据能更好地推断出北太平洋风暴路径上降水事件前后的大气环流背景,以此解释其降水分布,可为缺乏地面观测数据区域的降水研究提供参考。

The North Pacific storm path has an important impact on the global climate. Studying the structure of regional precipitation along the North Pacific storm path will help better understand the role of the storm path in transporting water vapor and heat to the global atmosphere. Base on the GPM data and the fifth generation reanalysis data(ERA5) from European center for medium range weather forecasts(ECWMF), taking an extratropical cyclone event that occurred in the storm track area of the North Pacificfrom December 20 to 24 in 2014 as an example, we analyzed the characteristics of precipitation and cloud parameter structures for three precipitation segments brought by thiscyclone. The results show that the synoptic conditions of the three precipitation segments are similar, and their water vapor distributions are different from the north to the south, resulting in different distributions of water vapor flux divergence, which makes the precipitation intensities in the three segments different. The precipitation is concentrated in the southeast side of cyclone center. By comparing the relationship between precipitation intensity and water vapor content in extratropical cyclones, it is found that more precipitable water does not necessarily lead to greater precipitation intensity, but the column integrated water vapor content determines the upper limit of precipitation intensity.There are evident conversion layers of ice water in the vertical cross-sections of the reflectivity in the three precipitation segments, and the distribution of ice water conversion layers in each segment is different. According to the particle spectra of three precipitation segments obtained by dual frequency rain radar(DPR), the intensity distribution of effective particle radius of each segment is in good agreement with that of the reflectivity, while the distribution of particle number concentration is not consistent with the former two. The mechanism remains to be studied in future. The fusion of the GPM and ERA5 data can better reflect the synoptic conditions before and after the precipitation event on the North Pacific storm path, so as to explain its precipitation distribution, which can provide a reference for precipitation study in the areas of lacking ground observation data.