长江中下游地区梅雨期降水的集合预报试验

本文利用MM5模式,通过改变模式的积云参数化方案、边界层过程和云微物理方案,构造了一个15个成员的集合预报系统,对2001年长江中下游地区梅雨期降水做了集合预报试验。试验表明,集合预报与决定预报相比,可以有效地提高梅雨降水的预报准确度;在不同分辨率条件下集合预报相对于决定预报的提高程度是不同的,分辨率越低,集合预报的价值越大。尽管如此,集合预报还具有的内在缺陷是对小雨高估、大到暴雨低估。试验也揭示了,MM5模式本身对于降水有过分预报的倾向,粗网格模式配置对细网格内降水产生重大影响。     

ALLOCATION DIFFERENCE ANALYSES OF WATER SUBSTANCES DURING TYPHOON LANDING PROCESSES

Based on a successful simulation of Typhoon Haikui (2012) using WRF (Weather Research & Forecasting) model with the WSM6 microphysics scheme, a high-resolution model output is presented and analyzed in this study. To understand the cause of the average gridded rainfall stability and increases after Haikui’s landfall, this research examines the fields of the physical terms as well as the vapor and condensate distributions and budgets, including their respective changes during the landing process. The environmental vapor supply following the typhoon landfall has no significant difference from that before the landfall. Although Haikui’s secondary circulation weakens, this circulation is not conducive to typhoon rainfall stability or increases, although the amounts of the six kinds of water substances (vapor, cloud water, cloud ice, snow, rain, and graupel) increase in the outer region of the typhoon. This reallocation of water substances is essential to the maintenance of rainfall. The six kinds of water substances are classified as vapor, clouds (cloud water and ice) and precipitation (snow, rain, and graupel) to diagnose their budgets. This sorting reveals that the changes in the budgets of different kinds of water substances, caused by the reduced mixing ratios of snow and ice, the water consumption of clouds, and the transformation of graupel, induce increased concentrations of precipitation fallout, which occur closer to the ground after typhoon landfall. In addition, this pattern is an efficient way for Haikui’s rainfall to remain stable after its landfall. Thus, the allocation and budget analyses of water substances are meaningful when forecasting the typhoon rainfall stability and increases after landfall.     

致洪暴雨过程中尺度涡旋的结构和准平衡特征分析

利用2008年6月广西致洪暴雨过程高分辨率数值模式资料,分析引起暴雨的中尺度涡旋在移动和持续性发展过程中其内部结构的演变以及系统的动力学特征。研究结果表明,中尺度涡旋是导致此次广西暴雨的主要系统,其发展移动过程中伴随有强烈上升运动的深厚湿对流,并在中高层持续形成明显的暖心结构。此次涡旋系统移动过程可分为涡旋南移和涡旋东移两个阶段,由于受到环境场的影响,涡旋中心区域动量、热量和水汽的再分配为其持续性发展提供有利条件。同时诊断分析表明,涡旋内部存在具有继发特征的长时间维持的组织化深厚湿对流系统,以强非地转分量为特征的超地转流,并表现出涡散运动共存且同量级的特征,具有典型的准平衡特征。