地形影响热带气旋“泰利”降水增幅的数值研究

利用NCEP/NCAR再分析资料与日本气象厅区域谱模式的融合资料,采用WRFV2.2模式研究了热带气旋“泰利”(0513)降水增幅过程中的大别山地形效应。结果表明,大别山地形对“泰利”降水影响明显,改变了降水增幅的中心位置,降水强度增幅约为15％,但是降水增幅是否发生与大别山地形无关。大别山地形的存在导致了地形辐合线和...     

登陆热带气旋与夏季风相互作用对暴雨的影响

利用《热带气旋年鉴》资料、NCEP/NCAR再分析资料采用动态合成分析方法,研究了登陆热带气旋降水与夏季风急流之间的关系,同时对登陆热带气旋与夏季风急流发生相互作用的典型个例强热带风暴Bilis (0604) 利用数值模拟方法研究了二者之间的相互作用对暴雨的影响。结果表明:登陆后造成大范围强降水的热带气旋往往与低层急流长时间相连,其水汽通量和潜热能显著大于弱降水热带气旋。数值试验结果表明:夏季风低空急流向热带气旋输送水汽对热带气旋结构维持有利,当水汽输送被截断后,热带气旋气旋性结构被破坏,强降水减弱、范围明显缩小;季风急流风速增强时可增加水汽通量输送,使得强降水范围增加、强度增强;在夏季风影响背景下,热带气旋在陆上的移动改变水汽和不稳定能量的分布,而热带气旋本身独特的动力结构使得强降水强度增加。     

2003—2005年西北太平洋台风眼生成特征分析

利用UW/CIMSS(University of Wisconsin-Madison/Cooperative Institute for Meteorological Satellite Studies)的AODT(Advanced Objective Dvorak Technique)资料和TRMM等卫星反演的每日海温资料,对西北太平洋2003—2005年热带气旋出眼规律及出眼条件进行了分析,包括有热带气旋成眼时的发展阶段、时间分布特征;热带气旋成眼时大尺度环境场条件(海温、垂直风切变)进行了统计研究,结果表明2003—2005年西北太平洋这40个热带气旋绝大多数(90%)在加强阶段开始出眼,只有4个热带气旋在成熟期才开始成眼;近92.5%的热带气旋发展到台风以上级别才开始出眼,也有一小部分的热带气旋在强热带风暴阶段出眼;热带气旋出眼的时间存在日变化,晚上出眼的热带气旋远少于白天出眼的热带气旋。80%的热带气旋出眼时所在位置的海表面温度在28 ℃以上。65%的热带气旋出眼时的垂直风切变是在6 m/s以下,只有4个热带气旋出眼时垂直风切变超过了10 m/s。综合以上结果表明只有能够发展为台风或已经发展成为台风的热带气旋才会有眼,且较高的海温和较弱的水平风场垂直切变非常有利于台风眼的形成。      

登陆台风变性过程的物理机制分析

0509号台风“Matsa”和0712号台风“Wipha”,均在中国大陆发生变性成为温带气旋。但前者变性后再度加强,后者变性后减弱消亡。用日本JRA25再分析资料,对其变性过程对比分析。表明：“Matsa”和“Wipha”均是在登陆后北上与中高纬西风槽相互作用的过程中,受到冷空气入侵后变性,从垂直对称分布演变为倾斜的非对称分布,且在北上过程中与中纬度高空锋区作用,但“Matsa”中心嵌入中纬度高空锋区,有再加强过程;而“Wipha”仅外围环流与锋区接触,中心未进入锋区,无再加强过程。通过对大气稳定度和垂直螺旋度等进一步分析表明：“Matsa”变性过程是系统性冷空气的南侵,而Wipha的变性只有弱冷空气的入侵;台风中心所在的垂直涡度ζ_p的增长大值区是否落在△θ_e<0的大气对流性不稳定的区域内,对台风变性后是否再加强有一定影响。此外,垂直螺旋度的高低空配置及正涡度柱与上升运动的相互配合是使台风变性加强的重要因素。     

热带气旋登陆维持和迅速消亡的诊断研究

采用动态合成方法, 对登陆后长久维持热带气旋(LTC)和迅速衰亡热带气旋(STC)的涡度、动能、热量和水汽的收支平衡进行计算和对比分析.结果表明: (1)LTC在陆上长久维持过程中, 其低层正涡度衰减缓慢并保持一定强度.STC登陆后正涡度减弱较快.(2)热带气旋登陆后涡度的收支主要取决于水平散度项、平流项和剩余项.散度项使LTC低层正涡度增加, 高层减少, 平流项和剩余项则使其低层涡度减弱, 高层涡度增加.总体而言, LTC自高层获得正涡度的补充, STC则没有获得环境正涡度.(3)低层, 摩擦耗散使LTC动能减少, 但动能通量辐合可补充部分动能而减缓衰减.中高层, LTC登陆后36～60 h动能收大于支, 动能的增加一部分来自于斜压动能制造, 一部分来自于次网格尺度.STC有类似的动能耗散, 却无动能补充.(4)LTC登陆后保持一定强度, 并从外界获得热量和水汽补充来支持积云对流发展, 而积云对流对LTC的维持具有正反馈作用.STC登陆后没有这一过程.     

EFFECT OF DRY COLD AIR ACTIVITY ON THE OFFSHORE RAPID INTENSIFICATION OF SUPER TYPHOON SAOMAI (2006): A NUMERICAL SIMULATION RESEARCH

Employing the mesoscale WRF (Weather Research and Forecast) model, Super Typhoon Saomai (2006) is simulated. The variation of track and intensity and its offshore rapid intensification process are well demonstrated by the model, and the temperature and humidity patterns associated with the dry cold air activity and their impact on and mechanism of the offshore rapid intensification of Saomai are mainly studied in this paper. The results indicate that high-resolution water vapor imagery can visually reveal the development, evolution, interaction as well as the mutual complementation of the dry cold air activity accompanied with the development of Saomai. The offshore rapid intensification phenomenon of Saomai is closely related to the dry cold air which originates from the upper- and mid- troposphere. Besides, the dry cold air from the upper troposphere is stronger than that from the mid-troposphere. Saomai intensifies as the dry cold air from the northwest moves toward its circulation but weakens when the dry cold air from the southwest is drawn into the storm. Dry cold airflows and their cold advection effect caused by the downward motion across the isentropic surface are favorable to the development of Saomai. The dry cold air always moves along an isentropic surface from the upper troposphere to the mid-troposphere around the typhoon circulation and contributes to Saomai’s abrupt intensity change.     

A STUDY ON VARIABLE QUANTITATIVE PRECIPITATION ESTIMATION USING DOPPLER RADAR DATA

With the pros and cons of the traditional optimization and probability pairing methods thoroughly considered, an improved optimal pairing window probability technique is developed using a dynamic relationship between the base reflectivity Z observed by radar and real time precipitation I by rain gauge. Then, the Doppler radar observations of base reflectivity for typhoons Haitang and Matsa in Wenzhou are employed to establish various Z-I relationships, which are subsequently used to estimate hourly precipitation of the two typhoons. Such estimations are calibrated by variational techniques. The results show that there exist significant differences in the Z-I relationships for the typhoons, leading to different typhoon precipitation efficiencies. The typhoon precipitation estimated by applying radar base reflectivity is capable of exhibiting clearly the spiral rain belts and mesoscale cells, and well matches the observed rainfall. Error statistical analyses indicate that the estimated typhoon precipitation is better with variational calibration than the one without. The variational calibration technique is able to maintain the characteristics of the distribution of radar-estimated typhoon precipitation, and to significantly reduce the error of the estimated precipitation in comparison with the observed rainfall.     

变性台风Winnie(9711)环流中的锋生现象

基于T106一日四次1.125°×1.125°格点资料, 采用非地转湿Ｑ矢量对登陆台风Winnie(9711)变性加强过程中环流内的锋生现象进行诊断分析。结果表明, Winnie变性加强与其环流内的中尺度锋生过程密切相关, 其低层环流中可发现包围台风中心的环状锋生现象。其中, 北侧锋带与西侧锋带在结构、性质上有所不同, 北侧锋具有暖锋特征, 而西侧锋具有冷锋特点。台风残余低压环流中心位于两条锋带的交汇处, 其变性加强过程类似于一个温带气旋在地面锋上的发展过程。Winnie变性加强过程中, 北侧暖锋锋生强, 锋面次级环流明显, 降水区主要出现在该锋带附近。西侧冷锋锋生弱, 无明显锋面次级环流, 降水不明显。强锋生区首先在台风上空高层产生, 随后增强下传, 加强了低层锋生过程。中低层锋生强度以及锋上垂直运动与凝结潜热作用有密切关系。     

登陆台风降水的大尺度环流诊断分析

强度相似的登陆台风造成的强降水可能差异很大.为研究大尺度环流对登陆台风降水的影响,利用热带气旋年鉴和NCEP/NCAR再分析资料,运用动态合成分析方法,对比分析了登陆后48小时内降水特征迥异而强度、路径相似的两组登陆台风的大尺度环流特征.合成分析结果表明,西南气流的水汽输送对台风降水至关重要,造成大范围强降水的台风往往在登陆后仍与深厚西南急流相连并持续很长时间.高空强辐散场是登陆台风造成大范围强降水的一个基本动力特征.造成强降水的登陆台风其环境场的上升气流不仅强,其气旋性环流的伸展高度高且能长时间维持.登陆台风造成降水的范围和强度与登陆前台风下游大陆环境大气的稳定度有关.下游高温高湿的大气有利于能量尤其是潜热能的大量补充,对强降水增强和维持都十分有利.因此,大尺度环流对登陆台风降水有明显影响.其中,与台风相连的西南急流强度和深厚程度是最重要的因子,高低空辐散辐合强度、台风及环境风场结构以及台风下游大陆上空大气湿热状态等都是需要加以考虑的.     

IMPACTS OF TWO TROPICAL CYCLONES EXPERIENCING EXTRATROPICAL TRANSITION DURING NORTHWARD PROGRESSION ON THE RAINFALL OF LIAODONG PENINSULA

Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.