GPM卫星探测新疆区域降雪敏感性及云结构特征研究

Sensitivity of GPM Satellite Detection of Snowfall and Analysis of Cloud Structure Characteristics in Xinjiang Region

目前人们对新疆干旱区降雪云结构特征的认知仍有限。利用2014—2021年GPM(global precipitation measurement)卫星搭载的测雨雷达DPR(dual-frequency precipitation radar)和微波成像仪GMI(GPM microwave imager)观测资料,对比了DPR不同产品对新疆区域降雪的敏感性及三类降雪云(深厚、浅薄和近地表)的宏微观特性差异,利用等频率高度统计方法,分析了四次新疆不同下垫面降雪云结构特征。结果表明:浅薄降雪云出现频率超过60%,而深厚降雪云对降雪量的贡献最大,三类云的液水路径(LWP)和冰水路径(IWP)集中在80~450 g·m^(-2)和100~380 g·m^(-2),回波顶高、LWP、IWP与近地表降水率总体上呈正相关;四次典型降雪系统分别发生在阿勒泰山区(A个例)、伊犁河谷(B个例)、古尔班通古特沙漠腹地(C个例)及昆仑山北麓戈壁地区(D个例),其中A、B个例主要为冰云,C、D个例多为冰水混合云,在GMI中166 GHz高频通道对降雪的敏感性较好,亮温分布在200~275 K;雷达反射率因子(Z)集中在16~25 dBz,对应高度为0.75~4.65 km,A、B和D个例云团存在“左倾”结构,Z集中在云体中上部,属于发展阶段,C个例的Z主要位于云体下部,云团处于成熟阶段。质量加权平均直径(D m)和粒子数浓度(dB N w)在1.00~1.22 mm和33~35产生的降雪量较大,降雪强度不仅与冰晶和过冷水粒子大小有关,还受到粒子数浓度的影响。研究成果对提升新疆地区降雪监测水平,深入认识该地区降雪形成机制及评估复杂地形条件下人工增雨(雪)潜力等具有积极意义。

Using the detection results of Global Precipitation Measurement(GPM)dual-frequency precipitation radar(DPR)and microwave imager(GMI)from 2014 to 2021,the differences in observing snowfall processes between different precipitation products of DPR are compared.Moreover,the macro and micro characteristics of three types of snowfall systems(deep,shallow,and near surface)are clarified,and the structural characteristics of four typical snowfall clouds in Xinjiang are analyzed by means of equal frequency height statistical method.The results show that the probability of shallow snowfall clouds exceeds 60%,while deep snowfall clouds contribute the most to snowfall.The liquid water path(LWP)and ice water path(IWP)of the three types of clouds are mostly distributed in 80-450 g·m^(-2)and 100-380 g·m^(-2),with a positive correlation between the echo top height,LWP,and IWP and the near-surface snowfall rate as a whole.The four selected cases are located in the Ale Mount Taishan area(A),the Ili River Valley(B),the hinterland of the Gurban Tunggut Desert(C),and the northern foot of the Kunlun Mountains in southern Xinjiang(D).The snow system observation results of GMI’s 166 GHz high-frequency channel are more detailed,and the brightness temperature is concentrated in the range of 200-275 K.Cases A and B are mainly ice clouds,and cases C and D are mostly ice water mixed clouds,and the snowfall intensity and area of the former are greater than the latter.The radar reflectivity factor(Z)of the cloud profile is concentrated in 16-25 dBz and 0.75-4.65 km height.Cloud clusters in cases A,B,and D exhibit a“left leaning”structure,with the highest echo intensity in the upper and middle parts of the cloud,belonging to a typical development stage of cloud cluster.The echo intensity of case C is mainly located in the lower part of the cloud,and the cloud cluster is in the mature stage.D m(mass weighted average diameter)and dB N w(particle number concentration)produce more snowfall between 1.00-1.22 mm and 33-35,respectively.The snowfall intensity is not only related to the particle size of ice crystals or supercooled water,but also affected by the particle number concentration.This study is of significance for improving the level of snow monitoring in Xinjiang,understanding the formation mechanism of snowfall and evaluating the potential and effectiveness of artificial snow seeding and cloud seeding in different regions of northern and southern Xinjiang.