西北太平洋热带气旋异常年的气候背景分析

本文从１９５３～１９８４年的３２年中挑选出７个热带气旋偏多年和７个偏少年，分析了与它们同期和前期的副热带高压、西风带纬向环流、北半球极涡以及赤道东太平洋海温、北极海冰的差异，发现其中的许多因子与热带气旋频数有很好的相关性，并指出在热带气旋年际变化这一时间尺度上，海洋因子的影响显得更重要。     

海洋对热带气旋响应的研究

建立一个二层非线性原始方程海洋模式，用以研究海洋对静止和以不同移速移动的热带气旋的响应。数值试验结果表明，海洋对静止ＴＣ的响应，具有不对移性；在ＴＣ中心处，抽吸使混合层变浅，在ＴＣ最大风速半径处，大风夹卷明显使ＭＬ加深和海表温下降；海洋对移动ＴＣ的响应，具有右偏性，且随移速加快而加剧。ＭＬ深度和ＳＳＴ的变化对ＴＣ移速十分敏感，而海流则不同。     

Computation of Wave, Tide and Wind Current for the South China Sea Under Tropical Cyclones

Based on the third-generation oceanic wave prediction model (WAVEWATCH Ⅲ) ,the third-generation nearshore wave calculation model (SWAN) and the mathematical tide, tidal current and cyclone current model, which have been improved, interconnected and expanded, a coupled model of offshore wave, tide and sea current under tropical cyclone surges in the South China Sea has been established. The coupled model is driven by the tropical cyclone field containing the background wind field. In order to test the hindcasting effect of the mathematical model, a comparison has been made between the calculated results and the observational results of waves of 15 cyclone cases, water levels and current velocities of the of 7 cyclones. The results of verification indicate that the calculated and observed results are basically identical.     

南海热带气旋纬向分布特征

根据中国气象局整编的1949~2003年台风年鉴资料,对南海热带气旋的源地、消亡地、强度、移向移速、活跃地等纬向分布的特征进行分析,旨在为南海热带气旋各纬度带的活动特征,为南海热带气旋的预报业务工作提供参考依据,并为研究工作奠定基础.     

0421号热带风暴"海马"登陆后的温带变性过程特征探讨

0421号热带风暴“海马”于2004年9月13日12:00在浙江温州市沿海登陆后,迅速减弱为热低压,然后继续北移;并在中高纬高空槽后的冷平流和中低纬低层暖式切变南部的暖平流共同作用下,低压加深及冷、暖锋生,发展为斜压温带锋面气旋.采用相对辐散作为气旋发展的判据,能很好地体现整个变化过程,气旋的移向基本上沿着相对辐散中心长轴方向移动.通过对地面温度场水平结构分析后发现,该气旋经历了3个阶段:暖涡旋基本对称结构、半冷半热非对称结构、冷涡旋基本对称结构.对流层低层气旋中心上空为暖平流区,引导气旋移动,而对流层中层的冷平流中心区一直位于气旋移向的下侧,推动气旋移动.     

黄、东海天气系统对渤海风暴潮影响

渤海沿岸是风暴潮多发区域。研究者多关心渤海局地风引起风暴潮变化,而忽略黄、东海天气系统对渤海风暴潮的影响。为研究外围天气系统对局地风暴潮的影响,本文采用实测资料对比和设计理想数值试验等方法,对黄、东海天气系统影响的渤海风暴潮进行了研究。结果表明:1、TY1814"摩羯"和TY1818"温比亚"台风风暴潮的实测资料呈现当黄、东海风力较大,而渤海风力较小时,渤海沿岸也会出现较大风暴潮现象; 2、从FVCOM(Finite-Volume Coastal Ocean Model)模拟的理想数值试验中发现,黄、东海风向是东南风时,引起渤海沿岸风暴增水极值最大;3、以入海气旋和登陆北上台风两种类型天气系统风向变化设计理想数值试验,发现黄、东海的东南风持续时间对渤海沿岸风暴潮极值大小和出现时间影响较大。理想试验获得的结论不仅能为渤海风暴潮预测和防灾减灾提供理论依据,还能够有效减少预警应急中漏报的现象,降低沿海经济损失。     

A Study on the Relationship Among Visibility, Atmospheric Suspended Particulate Concentration, and Meteorological Conditions in Hong Kong

By making use of the 2005 hourly data of visibility at Chek Lap Kok and suspended particulate (PM2.5) at Tung Chung,PM2.5 concentration and visibility (excluding cases with mist,fog, rain, or relative humidity≥95%) are found to have a reciprocal relationship with correlation coefficient about 0.8. Besides, similar seasonal trends are exhibited in both the number of hours of reduced visibility (visibility below 8 km and excluding cases with mist, fog, rain, or relative humidity≥95%) and PM2.5 concentration, i.e., with higher value attained in winter and lower value in summer.Backward trajectory analysis using HYSPLIT indicates that this phenomenon is related to the source of air mass affecting Hong Kong. For continental trajectories, the average daily occurrence of reduced visibility and the daily mean PM2.5 concentration were much higher than the corresponding occurrence of reduced visibility and mean PM2.5 concentration for maritime trajectories.A case study on an event with a tropical cyclone approaching Hong Kong is included in this paper to demonstrate the significance of meteorological conditions in determining the visibility and PM2.5 concentration.     

大尺度环流系统对西北太平洋变性TC频数影响的气候诊断分析

基于中国热带气旋年鉴资料,从气候学角度出发,对西北太平洋TC(热带气旋)发生温带变性的频数与大尺度环流系统间的关系进行了诊断和分析.研究发现变性TC多发生于夏、秋两季,通过对NCEP月平均再分析资料的500hPa高度场进行EOF分解,发现西北太平洋TC变性的频数与65°N附近强冷高压系统在夏、秋两季都存在着正相关关系,且相关性在秋季高于夏季;与30°N附近强副热带高压系统存在负相关关系,夏季副热带高压系统的作用更大;与30°N以南西北太平洋多台风活动区域的弱低压存在显著的负相关,低压越弱,对流越弱,则TC的生成数越少,其中发生变性的TC数也会减少.500hPa高度场EOF分解的第一特征向量所对应的时间函数分布在20世纪70年代中期前后出现了反号,较好地对应了变性TC年频数的年际变化趋势,70年代中期之前变性TC呈总体偏多,之后变性TC的频数总体偏少,呈明显下降趋势.     

Derivation of Parametric Tropical Cyclone Models for Storm Surge Modeling

In this paper, the parametric tropical cyclone models for storm surge modeling are further developed. Instead of tangential wind speed via cyclostrophic balance and radial wind speed using a simple formulation of defection angle, the analytical expressions of tangential and radial wind speed distribution are derived from the governing momentum equations based on the general symmetric pressure distribution of Holland and Fujita. The radius of the maximum wind is estimated by tropical cyclone wind structure which is characterized by the radial extent of special wind speed. The shape parameter in the pressure model is estimated by the data of several tropical cyclones that occurred in the East China Sea. Finally, the Fred cyclone (typhoon 199417) is calculated, and comparisons of the measured and calculated air pressures and wind speed are presented.     

Ensemble Forecasts of Tropical Cyclone Track with Orthogonal Conditional Nonlinear Optimal Perturbations

This paper preliminarily investigates the application of the orthogonal conditional nonlinear optimal perturbations(CNOPs)–based ensemble forecast technique in MM5(Fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model). The results show that the ensemble forecast members generated by the orthogonal CNOPs present large spreads but tend to be located on the two sides of real tropical cyclone(TC) tracks and have good agreements between ensemble spreads and ensemble-mean forecast errors for TC tracks. Subsequently, these members reflect more reasonable forecast uncertainties and enhance the orthogonal CNOPs–based ensemble-mean forecasts to obtain higher skill for TC tracks than the orthogonal SVs(singular vectors)–, BVs(bred vectors)– and RPs(random perturbations)–based ones. The results indicate that orthogonal CNOPs of smaller magnitudes should be adopted to construct the initial ensemble perturbations for short lead–time forecasts, but those of larger magnitudes should be used for longer lead–time forecasts due to the effects of nonlinearities. The performance of the orthogonal CNOPs–based ensemble-mean forecasts is case-dependent,which encourages evaluating statistically the forecast skill with more TC cases. Finally, the results show that the ensemble forecasts with only initial perturbations in this work do not increase the forecast skill of TC intensity, which may be related with both the coarse model horizontal resolution and the model error.