大气环状模对夏季中国大陆登陆热带气旋频数气候变化的影响

采用1949—2016年7—8月美国国家环境预报中心及大气研究中心(NCEP/NCAR)再分析资料与中国气象局(CMA)上海台风所整编的热带气旋最佳路径数据集,研究大气环状模(Circumglobal Teleconnection,CGT)与中国大陆地区登陆热带气旋(Tropical Cyclone,TC)频数气候变化的关系。定义200 hPa经向风经验正交展开(EOF)的第一模态为CGT,其时间系数为环状模指数(Circumgolbal Teleconnection Index,CGTI)。CGT在北半球中纬度地区有5个异常中心,CGTI在1949—2016年呈明显的下降趋势,且存在一个2~3 a的周期振荡。CGT与大尺度环流异常存在密切的联系。研究表明:CGTI与中国大陆登陆TC频数气候变率具有显著的正相关,即CGTI表现为正异常时,登陆中国大陆的TC频数增加,反之减少。当CGT表现为正位相时,东亚副热带西风急流增强,急流南侧的反气旋切变增强,使TC登陆过程的活动区域200 hPa的辐散增强,此外,对流层高层Rossby波能量向南传播增强,形成波通量辐合,导致东风异常,产生了东风异常的引导气流和纬向风垂直切变,东风切变使得切变减小,增加了TC登陆中国大陆的可能性。     

RESEARCH ON THE INTERANNUAL AND INTERDECADAL VARIABILITIES OF THE MONSOON TROUGH AND THEIR IMPACTS ON TROPICAL CYCLONE GENESIS OVER THE WESTERN NORTH PACIFIC OCEAN

In this paper, we mainly summarize and review the progresses in recent climatological studies (by CMSR, IAP/CAS and some associated domestic and international institutions) on the interannual and interdecadal variabilities of monsoon troughs and their impacts on tropical cyclones and typhoons (TCs) geneses over the western North Pacific Ocean. The climatological characteristics of monsoon troughs and four types of circulation patterns favorable to TCs genesis over the western North Pacific Ocean in summer and autumn are given in this paper. It is also shown in this paper that the monsoon trough over the western North Pacific Ocean has obvious interannual and interdecadal variabilities. Especially, it is revealed in this paper that the interannual and interdecadal variabilities of the monsoon trough over the western North Pacific Ocean influence the TCs genesis not only through the impact on distributions of the vorticity in the lower troposphere and the divergence in the upper troposphere, the water vapor in the mid- and lower troposphere and the vertical shear of wind fields between the upper and lower troposphere over the western North Pacific Ocean, but also through the dynamical effects of the transition between convectively coupled tropical waves and providing disturbance energy. Besides, some climatological problems associated with TCs activity over the western North Pacific Ocean that need to be studied further are also pointed out in this paper.     

新疆冰雹天气的气候特征分析

根据1961～1999年新疆90个气象观测站的地面观测资料，统计分析了新疆冰雹的时空分布特征，并以分钟为单位给出冰雹的日变化和持续时间。新疆冰雹主要出现在西部和中部山区，集中出现在4～10月。降雹一般出现在下午，傍晚是高峰期，有60％的冰雹持续时间在6分钟以内。进一步普查39年冰雹天气资料，得到76次系统性冰雹天气过程和1279次局地冰雹天气过程，局地冰雹天气过程的发生远远多于系统性冰雹天气过程。冰雹天气过程与地形密切相关，主要发生在山区。冰雹天气过程以1天为主，多发生于夏季，系统性冰雹天气过程均由中尺度高压造成。     

Effects of the East Asian summer monsoon on tropical cyclone genesis over the South China Sea on an interdecadal time scale

Tropical cyclone (TC) genesis over the South China Sea (SCS) during 1965-2004 was analyzed.The locations of TC genesis display evident seasonal changes,with the mean position of formation situated nort...     

用数字云图确定热带气旋强度方法的检验和应用

以关岛飞机探测的热带气旋资料和登陆热带气旋的实测风资料为观测值，将用数字云图确定的热带气旋强度与观测值作比较，其平均绝对误差均不足3 ms-1。文章还给出了1994年业务试用结果。检验结果表明，此方法具有业务应用价值。     

碘化银播撒对云和降水影响的中尺度数值模拟研究

通过在WRF (Weather Research and Forecasting) 中尺度天气数值模式中引入碘化银与云相互作用过程, 建立了中尺度播撒碘化银数值模式。研究了碘化银播撒对于中尺度对流天气过程中云和降水的影响, 研究了不同播撒部位、 播撒时间和播撒剂量情况下碘化银的扩散、 传输及其对云中水成物和降水量的影响。研究结果表明, 碘化银在云中的扩散传输过程与播撒的位置有很大关系, 在最大上升气流区播撒的碘化银能随着气流更快地扩散到云体上部过冷水含量丰富的区域, 播撒在云上层入流区和云下层入流区的碘化银扩散到云中过冷水区需要时间更长, 同时有大部分停留在云体边缘。碘化银能与云中过冷水相互作用, 消耗过冷水使云中冰晶数浓度明显增加, 从而使霰粒子转化减少, 过冷水更多地转化为雪粒子, 过冷水凝结释放出潜热使上升气流增强, 促进了对流发展。由于雨水含量的增加, 地面降水也出现增加。碘化银播撒率对地面降水量影响很大, 当播撒率为0.6 g/s时, 播撒对降水的影响时间超过4小时, 增雨的效果更好。播撒率为0.1 g/s时增雨效果不明显, 当播撒率为1.2 g/s 时, 对总降水可能出现抑止作用。对比碘化银播撒率为0.6 g/s时12小时地面增雨量, 在云上层入流区播撒碘化银试验中, 地面增雨量比对最大过冷水含量区的催化试验提高了48.7%, 最大上升气流区播撒试验增雨效果最好, 地面增雨量比在最大过冷水区域播撒提高了72.1%。     

梅雨锋上MCS的发展、传播以及与低层"湿度锋"相关联的CISK惯性重力波

采用一个包含简单积云对流参数化的线性模式讨论在长江流域相当正压性质的梅雨锋上,贯穿整个对流层的深厚惯性重力波的发生、传播和频散性质.结果表明,与积云对流加热场有最密切关系的低层湿度条件及其水平分布不均匀性质都对扰动的波速和稳定度有重要影响,最有利出现不稳定发展的地方是在"低层湿度锋区"南界附近,因此这里是中尺度对流系统(MCS)的活跃地带.关于频散性质的分析表明,能允许群速度大于相速度的低层湿度条件及其水平分布的特征值范围比较宽.而在上述稳定度接近中性的条件下最有利于出现沿"湿度锋区"轴向的上、下游效应.这个结果也许能很好地解释:在梅雨锋上,恰恰是当一个旺盛的MCS达到顶点而开始趋向衰减时,在它的上、下游很快发展起新的MCS,新、旧MCS一起形成"云团波串"这样一个重要而有趣的观测事实.     

东北冷涡研究概述

简述了东北冷涡的形势特征、气候特征、天气特征与强对流特征;回顾、综述了东北冷涡形成、发展、维持、消退期的研究成果,特别是东北冷涡强对流特征的研究进展;讨论了东北冷涡强降水、强天气等预报业务的难点及其研究方面存在的问题。认为：需要依靠现代雷达、卫星等观测设备和数值模拟手段,加强东北冷涡暴雨及强天气机制研究,提高东北冷涡天气的预报水平。     

爆发性气旋的锋生位涡反演诊断

本文采用基于埃特尔位涡反演诊断和锋生函数诊断的锋生位涡反演诊断方法,对一次发生在西太平洋地区的爆发性气旋过程进行了诊断分析和机制研究。本文主要从锋生演变的角度,定量诊断了与对流层顶折迭现象相联系的高层位涡扰动,由凝结潜热释放造成的中层位涡扰动,与低层锋区扰动相联系的低层位涡扰动以及以低层水平辐合辐散为主要成份的非平衡风场在气旋发生发展的不同阶段所起的作用和影响,并对以上各物理过程相互作用,造成气旋爆发性发展的机制进行了分析讨论。     

Kinematic structure of a heavy rain event from dual-Doppler radar observations

The detailed kinematic structure of a heavy rain event that occurred in the middle reaches oi the Yangtze River was investigated using dual-Doppler radar observation. A variational analysis method was developed to obtain the three-dimensional wind fields. Before the analysis, a data preprocessing procedure was carried out, in which the temporal variation with the scanning time interval and the effect of the earth curvature on the data position were taken into account. The analysis shows that a shear line in the lower and middle levels played an important role in the rainfall event. The precipitation fell mainly on the south end of the shear line where southerly flow prevailed and convergence and updraft were obvious. With the movement and decay of the shear line, the precipitation moved and decayed correspondingly.