热带气旋进入北部湾后强度突变的天气气候特征分析

本文按近海热带气旋强度突变的标准，对１９７０～１９９０年进入北部湾后强度发生突变的热带气旋进行分类统计，发现有如下的气候特征：每年平均有３２个热带气旋进入北部湾，其中强度变化不大的占总数的５２％；强度突然减弱的占总数的４２％；强度突然增强的占总数的６％。强度变化不大和强度突然减弱的发生在５～１１月，强度突然增强的发生在８～９月。本文对进入北部湾的热带气旋强度增强的天气类型进行分类，归纳起来分为四种天气类型：副热带高压型；赤道辐合带型；季风低槽型和锋面低槽型，这些结果将对天气预报有很大的帮助     

遗传算法与神经网络相结合的热带气旋强度预报方法试验

以1960~2001年共41 a的7月和8月西行进入南海海域的热带气旋样本为基础,采用遗传算法与神经网络相结合的方法,进行了热带气旋强度预报模型的预报建模研究.并根据相同的热带气旋个例,将这种遗传-神经网络热带气旋强度预报模型与气候持续法热带气旋强度预报方法进行对比分析,试验预报结果表明,遗传-神经网络方法具有更好的预报能力.     

Microwave Remote Sensing of Tropical Cyclones from Space

This article reviews several microwave instruments employed in research and analysis of tropical cyclones (TCs), typhoons, and hurricanes. The instruments discussed include scatterometers, microwave radiometers, synthetic aperture radars (SARs), and rain radar from space. Examples of the particular contribution by one or more of these instruments in analysis of several storms illustrate the comprehensive new views provided by the SeaWinds scatterometers, the detailed high-resolution wind field provided by RADARSAT-1 SAR, particularly inside and in the vicinity of hurricane “eyes,” and the presence of secondary flows in the region between rainbands in TCs. The high spatial resolution of precipitation data from the Tropical Rainfall Measuring Mission's rain radar, combined with scatterometer or SAR data, give a significant improvement in the details that can be seen from space, at the surface, and in the precipitating areas of TCs. The microwave instruments provide a penetrating view below the upper level cirrus clouds. This revised version was published online in August 2006 with corrections to the Cover Date.     

“浣熊”强度变化的环境背景和卫星观测分析

利用实况观测定位和强度资料、NCEP的1°×1°全球最终分析资料、NOAA周平均1°×1°海温再分析资料和FY卫星水汽图像,分析台风浣熊(0801)的环境背景条件和内核结构演变与强度变化的关系.结果表明:(1)环境风垂直切变增大至10m·s~(-1)左右与南海北部海表温度逐步减小导致最大可能强度不断降低是"浣熊"快速发展过程中断并减弱的重要外部条件;(2)卫星水汽图像显示内核结构存在眼壁破裂和复原现象,该现象精确地反映其强度变化.眼壁破裂(复原)过程导致"浣熊"减弱(增强).     

2006年超级台风“桑美”强度与结构变化的数值模拟研究

使用一个高分辨率、非静力数值模式WRF模式对2006年超级台风Saomei强度和结构进行了数值模拟研究.首先,评估了Makin的粗糙度长度公式对台风Saomei强度和结构变化的影响,结果表明,采用新参数后,使得模拟的台风强度变化与实况最佳路径资料的强度变化更一致,对超级台风Saomei强度预报有改进;但对台风路径的影响不大.通过QuikSCAT、雷达和TRMM非常规资料的验证,进一步表明模拟的台风Saomei的结构与实况很接近,可以再现台风内核区域的部分"双眼墙"和"Annular"结构.其次,通过对台风Saomei边界层过程模拟的改进,表明在平均风速大于40 m/s时边界层各物理量明显改善,使得模式最大强度比传统的简单外推插值方案有显著改进,特别是在台风最强阶段,当台风Saomei眼墙区域的海表面拖曳系数C_d的相对变小,使得其眼墙区域的平均切向风速、径向风速、垂直风速、温度距平、涡旋动能和绝对角动量等物理量均有增强.表明台风Saomei眼墙氏域(20-40 km)各物理量的贡献对其强度和结构变化的影响十分重要.最后,在此基础上进一步分析模式海温和大尺度环境垂直风切变对台风Saomei强度和结构变化的可能影响,讨论了台风Saomei在其增强和消弱阶段中,大尺度环境垂直风切变对其强度变化的负反馈作用.     

ANALYSIS OF RAINSTORMS ASSOCIATED WITH SIMILAR TRACK TROPICAL CYCLONES HAITANG (0505) AND BILLS (0604)

It is generally thought that the influence of comparable track typhoons is approximately similar,but in fact their wind and especially their rainstorm distribution are often very different. Therefore,a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604),which are of a similar track,is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainthll of TC itaitang (0505) and Bills (0604) is diagnosed and compared.The result indicates that these two TCs have similar precipitation distribution before landtall but different precipitation characteristics after landthll. Using NCEP/GFS analysis data,the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence.The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bitis (0604) before landlhll results ti'om a peripheral easterly wind,a combination of the tropical cyclone and the terrain. After landthll and moving far inland of the storm,the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing thctors to heavy rainstorms in southeast Zhejiang is a southeast jet stream,which is maintained over the southeast coast. In contrast,the South China Sea monsoon circulation transports large amounts of water vapor into Bills - when a water-vapor transport belt south of the tropical cyclone significantly strengthens - which strengthens the transport. Then,it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland,the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary,combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.     

Effect of tropospheric temperature change on the zonal mean circulation and SH winter extratropical cyclones

This study aims to understand the mechanisms which cause an overall reduction of SH extratropical cyclone activity with a slight increase in the high latitudes in a warmer climate simulated in general circulation models (GCMs) with increasing CO₂. For this purpose, we conducted idealized model experiments by forcing warm temperature anomalies to the areas where climate change models exhibit local maximum warming—the tropics in the upper troposphere and the polar regions in the lower troposphere—simultaneously and separately. The Melbourne University atmospheric GCM (R21) coupled with prescribed SST was utilized for the experiments. Our results demonstrate that the reduction of SH extratropical cyclone frequency and depth in the midlatitudes but the slight increase in the high latitudes suggested in climate change models result essentially from the tropical upper tropospheric warming. With this tropical warming, the enhanced static stability which decreases baroclinicity in the low and midlatitudes turns out to be a major contributor to the decrease of cyclone activity equatorward of 45°S whereas the increased meridional temperature gradient in the high latitudes seems an important mechanism for the increase of cyclone activity over 50°–60°S.     

Future impact of anthropogenic sulfate aerosol on North Atlantic climate

We examine the simulated future change of the North Atlantic winter climate influenced by anthropogenic greenhouses gases and sulfate aerosol. Two simulations performed with the climate model ECHAM4/OPYC3 are investigated: a simulation forced by greenhouse gases and a simulation forced by greenhouse gases and sulfate aerosol. Only the direct aerosol effect on the clear-sky radiative fluxes is considered. The sulfate aerosol has a significant impact on temperature, radiative quantities, precipitation and atmospheric dynamics. Generally, we find a similar, but weaker future climate response if sulfate aerosol is considered additionally. Due to the induced negative top-of-the-atmosphere radiative forcing, the future warming is attenuated. We find no significant future trends in North Atlantic Oscillation (NAO) index in both simulations. However, the aerosol seems to have a balancing effect on the occurence of extreme NAO events. The simulated correlation patterns of the NAO index with temperature and precipitation, respectively, agree well with observations up to the present. The extent of the regions influenced by the NAO tends to be reduced under strong greenhouse gas forcing. If sulfate is included and the warming is smaller, this tendency is reversed. Also, the future decrease in baroclinicity is smaller due to the aerosols’ cooling effect and the poleward shift in track density is partly offset. Our findings imply that in simulations where aerosol cooling is neglected, the magnitude of the future warming over the North Atlantic region is overestimated, and correlation patterns differ from those based on the future simulation including aerosols.     

温室气体浓度增加情景下西北太平洋热带气旋变化的模拟分析

利用德国Max-Planck气象研究所参与政府间气候变化委员会(The Intergovernmental Panelon Cli-mate Change,IPCC)第四次评估报告的气候系统模式(ECHAM5/MPI-OM)的数值模拟结果,分析研究了全球增暖背景下西北太平洋热带气旋的变化。结果表明,ECHAM5模式较好的模拟出了热带气旋的基本结构和频数的分布特征。当大气中CO2浓度增加时,热带气旋中心的最低气压升高,850hPa正涡度降低,风速减小,风场出现反气旋性环流异常,暖心强度减弱,气旋的低层径向流入和高层径向流出减少,气旋总体强度减弱。CO2浓度的增加会总体上减少西北太平洋热带气旋的生成频数,从模拟结果看年均减少10个左右。就CO2浓度增加对热带气旋频数季节变化的影响而言,CO2浓度增加所引起气旋频数减少较平均的分配到多个月份里,表明CO2浓度增加引起的大气环流异常在全年都会对西北太平洋热带气旋的发生频数产生影响。分析加拿大参加IPCC第四次评估报告的CGCM3.1(T47)模拟资料,其结果与ECHAM5资料得到的结果大致相似。     

DEVELOPING AND NON-DEVELOPING TROPICAL CYCLONES AS REVEALED BY HIGH DENSITY CLOUD MOTION WINDS

An algorithm for computation of cloud motion winds has been developed at the National Satellite Meteorological Center in China. Since 1997, it has been applied to calculate the cloud motion winds for a 1.25 lat. 1.25 long. mesh over the northwest Pacific region with the satellite data from GMS-5. The development of the tropical cyclones is studied. It shows that the tropical cyclone is usually intrigued by the westerly jet streams at the upper levels of the troposphere, which may be caused by mid-latitude troughs well extending into the tropics. During the prime season of summer, the westerly flowing equatorward of the TUTT may also be a cause for the generation of typhoons.