海南岛冷空气降水天气形势差异分析

利用2000—2017年海口常规探空资料、海南岛18个国家气象站的日降水量和欧洲中期数值预报中心再分析资料（ECMWF-Interim），采用REOF和k-means聚类相结合的方法，对冷空气低空偏东急流（LLEJ）背景下海南岛暴雨和少雨两类天气的环流形势分别进行分类。结果表明：导致海南岛暴雨和少雨的主要环流形势分别有两种。总体上，暴雨型中的海南岛水汽输送条件以及抬升触发条件较好，而无雨型中海南岛受下沉运动控制，水汽输送条件一般。其中，暴雨Ⅰ型中海南岛低层至中高层深厚的偏东气流输送水汽和暖湿不稳定能量，较强锋面的抬升作用使不稳定能量释放导致强降水；暴雨Ⅱ型中海南岛低层（850 hPa以下）偏东气流输送水汽，南支槽和较弱锋面的抬升作用触发较强降水的发生；少雨Ⅰ型中海南岛受较强干冷空气影响，500 hPa为偏西风影响，700 hPa为反气旋环流控制，低层水汽条件差；少雨Ⅱ型中海南岛受西太平洋副热带高压环流影响为主，700—500 hPa皆位于反气旋环流中心附近，以下沉运动为主。

Analysis of the background differences of precipitation influenced by cold air in Hainan island

In this study,using the data from the conventional soundings,the daily precipitation amount from 18 national weather stations in Hainan island,and the ERA-interim reanalysis in 2000-2017,the circulation types corresponding to heavy rain and weak rain events in Hainan island affected by cold low level easterly jet(LLEJ)were classified by the means of REOF(Rotated Empirical Orthogonal Function)and k-means clustering.The results show that two circulation types that lead to the heavy rain and weak rain events in Hainan island are identified.In general,the heavy-rain events have better water vapor and updraft conditions,while the weak-rain ones are relatively poor in the water vapor supply.For the type I of heavy-rain events,the water vapor is transported by a deep eastward airflow from the surface to high level and is uplifted by the strong fronts resulting in strong precipitation.For type II of heavy-rain events,an easterly airflow below 850 hPa conveys water vapor to Hainan island,and the updraft lifting by the South Branch Trough and surface fronts results in heavy rainfall.For the type I of weak-rain events,Hainan island is affected by a strong dry cold air,with westerly airflow at 500 hPa and anticyclone circulation at 700 hPa,and the water vapor conditions at low level are poor.For the type II of weak-rain events,Hainan island is mainly affected by the western Pacific Subtropical High circulation,and the anticyclonic circulation from700 hPa to 500 hPa results in a subsidence motion.