台风“威马逊”登陆后长时间维持原因分析

超强台风威马逊(1409)在华南三次登陆,登陆后减弱缓慢,带来了狂风暴雨和巨大的经济损失。利用NCEP再分析资料、CMABST最佳台风路径数据等资料,对"威马逊"长时间维持的原因进行天气学和动力学诊断分析,结果表明:(1)500hPa副高西伸发展,紧随着台风,副高和台风环流之间维持较强的气压梯度和水汽输送,有利于台风环流的维持。850hPa西南季风急流和越赤道气流合并卷入台风低压环流中,输送的水汽和不稳定能量是台风在登陆后衰减缓慢的重要原因。高空存在强流出气流,高层辐散抽吸作用有利于台风强度的维持和发展。(2)台风移向下游区域海温偏高、环境风垂直切变小、强盛水汽输送是台风强度维持的重要环境条件。台风登陆后涡度和垂直速度结构完整,减弱缓慢,利于台风环流的维持。台风移入的华南地区处于热力不稳定状态,有利于对流凝结潜热效率的增加和台风环流内对流活动的增强,从而有利于台风强度的维持。     

超强台风“威马逊”近海急剧加强特征及诊断分析

利用NCEP/NCAR提供的全球客观分析资料对1409号超强台风“威马逊”近海急剧加强的特征进行了诊断分析。结果表明：南海较高的海表温度、中低层丰富的水汽净流入为“威马逊”增强提供了有利的能量条件;维持近22 h对流层深层、高层及低层介于0~4 m/s弱环境风垂直切变是“威马逊”两次以超强台风登陆的必要条件;台风中心附近对流层高层强烈辐散、中低层正涡度值的增大和正涡度柱向对流层上层的伸展导致“威马逊”急剧增强;“威马逊”台风急剧增强具有一定前兆性,急剧增强与环境风垂直切变及对流层中低层涡度值的响应时间分别为12 h和9 h。     

强台风"云娜"登陆过程的研究——基于AREM模式的数值分析

使用新改进的双重嵌套AREM数值预报模式,并与高时空分辨率的探测资料相结合,针对台风“云娜”登陆加强的特点进行数值模拟分析,结果表明该模式对“云娜”台风环流特征、强度变化趋势和台风降雨等都有较强的预报能力。在此基础上,定量研究其登陆加强过程中三维大气中尺度场动、热力特征及演变过程,并探讨了其登陆加强的机理。由此得出了与“云娜”登陆加强相关的重要影响因子:(1)副热带高压西南侧的偏东引导气流加强是“云娜”登陆前移速加快、强度增强的有利环境场条件。(2)“云娜”近海移速加快时有较强的东密西疏的不对称流场结构,特别是其垂直速度场以及强对流发展的水平分布的强不对称特征与该气旋登陆加强同时发生,也可能与台风强度维持和加强存在一定的相关。(3)在“云娜”中心西南侧的强凝结潜热释放过程,有可能助其在登陆时加强。此外,在“云娜”发展加强阶段,低层暖湿、中层干冷的位势不稳定层结,有利于对流的强盛发展。(4)“云娜”登陆前后有强低空急流与之联结,并有垂直对流运动发展,由此可获得不断增强的潜热能量是其登陆加强的另一个重要机制。     

台风凤凰形成发展过程中对流凝结潜热和感热的作用

应用NCEP再分析资料,计算分析了台风凤凰发生和发展过程中的积云对流潜热加热和海面感热通量.表明:感热释放通过海气相关作用使海面风及对流层涡度增强,可能是台风初始低压的形成机制;积云对流潜热释放不但使台风中心增暖并使台风中间层上升运动增强,从而促使台风加强和发展,因此,对流凝结潜热是台风凤凰维持和发展的主要热力和动力因子.     

2008年台风“风神”强迫次级环流的诊断分析

利用WRF（weather research and forecasting）模式模拟资料对2008年06号台风“风神”进行诊断分析,采用准地转PV-ω方程对台风外围中尺度对流系统较强的6月20日10时（世界时）的资料进行分析.通过PV-ω方程诊断了潜热、摩擦及干动力过程对台风次级环流的作用,结果显示潜热强迫产生的次级环流最强,摩擦强迫主要集中在边界层,而干动力过程则在台风中心附近产生影响.加入摩擦、潜热得到的准平衡流场能够描述70％左右的台风环流.环境垂直切变在台风中心附近强迫产生横向次级环流的垂直切变与环境垂直切变相反,次级环流会使得台风一侧的上升气流减弱而另一侧上升气流增强,从而使得台风不对称增强.同时,发现垂直切变可能在其最大垂直切变方向右侧激发台风外围中尺度系统.通过构造理想的准平衡的台风及叠加在其上的中尺度系统环流,选择不同的切变和环境平均气流,发现增大切变会使得强迫次级环流增强,而增大环境平均气流不一定能够使得强迫次级环流增大,反而可能使得强迫次级环流减弱.通过诊断发现由切变强迫次级环流造成的中尺度对流系统上方扰动可能是中尺度对流系统持续存在的原因.     

“威马逊”（1409）强降水物理过程模拟诊断研究

利用WRF模式,结合三维降水诊断方程和降水效率定义,针对1409号超强台风“威马逊”临岸迅速加强为超强台风并登陆我国华南沿海这一时段的强降水物理过程开展了高分辨率数值模拟诊断研究。结果表明,“威马逊”主体环流区域内一直维持很强的平均降水强度（P_S）,陆地和海洋P_S的相对贡献基本呈反向变化,登陆期间陆面摩擦辐合增强,有利于水汽更多地向陆地区域辐合（Q_WVA代表垂直积分的三维水汽通量辐合/辐散率,此时段Q_WVA为正值）,造成登陆前短时段内陆地上空局地大气增湿（Q_WVL代表垂直积分的水汽局地变化率的负值,此时段Q _WVL为负值）,借助云微物理过程快速转化为液相和固相云水凝物（Q_CLL和Q_CIL分别代表垂直积分的液相和固相云水凝物局地变化率的负值,此时段Q_CLL和Q_CIL为负值）,促使陆地上空降水云系快速发展和降水强度增强,而当环流中心位于北部湾洋面时,海洋Q_WVA的相对贡献显著增强,登陆期间下垫面的变化导致水汽相关物理过程明显变化,进而造成降水云系和强降水中心的显著变化;与陆地相比,海洋表面蒸发的作用更强,变化更明显;“威马逊”影响华南沿海期间,主体环流圈内平均的Q_CLL和Q_CIL均基本呈现“正—负—正”的变化特征,当环流中心位于北部湾洋面（三次登陆时期）时水凝物含量以增加（减少）为主;“威马逊”主体环流区域内一直维持高降水效率,从主体环流圈接触陆地开始,陆地降水效率迅速升高,而海洋降水效率在绝大多数积分时段内维持较高数值,只在第二和第三次登陆后有所降低。     

准平衡和非平衡流对台风百合（2001）内中尺度深厚湿对流的影响

利用台风百合(2001)的高分辨率模式资料, 应用PV－ω反演方法, 在分析台风准平衡和非平衡垂直环流基本特征的基础上, 诊断研究了热力和动力强迫对台风深厚湿对流结构的影响, 结果指出: 准平衡流能够描述台风中具有较长生命史过程的中尺度对流系统的环流结构, 中层大振幅垂直运动主要由准平衡ω方程中凝结潜热释放的热力强迫所决定; 台风低层由动力辐合强迫产生的弱对流, 对眼墙区深厚湿对流的形成起到触发作用; 而高层动力强迫产生的下沉运动则削弱了凝结潜热项的影响, 抑制了垂直运动向高层伸展。非平衡垂直环流结构上呈现的短波振荡和快时间尺度调整的时空分布特征表明, 它是与重力快波频散过程相联系的非定常环流。分析台风中深厚湿对流形成的物理模型可知, 准平衡动力强迫引起的低层弱对流达到一定振幅, 则会引起中层水汽相变引起的凝结潜热反馈, 使得准平衡和非平衡流叠加形成了眼墙区上升运动的大值中心, 加上非平衡垂直环流对动量和热量起到的补偿和调整作用, 构成了台风内中尺度深厚湿对流的组织化过程。     

台风“米克拉”在台湾海峡南部快速增强的原因分析

利用欧洲中期天气预报中心ERA-Interim再分析资料、中国气象局台风最佳路径资料、 NOAA逐日最优海表温度（OISST）、Himawari-8卫星观测资料以及中国地面自动气象站观测资料等,分析了台风“米克拉”近海强度预报的难点,并研究了导致“米克拉”在台湾海峡南部快速增强的环境因子,探讨了“米克拉”在较强环境风垂直切变下快速增强过程中对流非对称分布特征。结果表明：（1）台风“米克拉”在较强200—850 hPa环境风垂直切变下在台湾海峡南部海域发生了快速增强,并以峰值强度在福建登陆,非常少见,造成预警时间短,强度预报难度大;（2）有利的海洋热状况和大气环流环境条件,如中国南海北部海温异常偏高,南亚高压南侧东风急流与“米克拉”相互作用引起的强烈高层出流以及强劲稳定西南季风气流带来的充沛水汽输送,均对台风“米克拉”在台湾海峡南部海域快速增强起重要作用;（3）台风“米克拉”快速增强过程中,传统业务主要关注的200和850 hPa之间的环境风垂直切变较强,但从环境风的垂直结构分析发现切变主要集中在对流层中、高层,而中、低层切变较小,且中、高层环境风垂直切变对台风增强的抑制作用相对中、低层...     

双台风“纳沙”和“海棠”登陆后强度变化成因及对比分析

利用NCEP（National Centers for Environmental Prediction）再分析资料对2017年双台风“纳沙”（1709）和“海棠”（1710）先后登陆福建后的强度变化特征进行对比分析。结果表明：低纬水汽输送的强弱变化是造成双台风强度变化的主要原因,而越赤道气流对水汽输送起到关键作用。副热带西风急流与中低空风场强弱变化一致,西风急流增强伴随中低空东风加强是“海棠”陆上强度维持不减的原因之一,反之“纳沙”快速减弱。双台风效应对强度变化也起着重要作用：双台风靠近相吸作用下,“纳沙”残余环流卷入“海棠”环流中,为其输送正涡度因子及斜压能量,也是促使“海棠”强度维持的原因。台风登陆后,其上空三种不同层差的垂直风切变值表现一致减小的变化趋势及低于6 m·s^-1的风切,有利于弱台“海棠”陆上长久维持。海岸锋生及海表通量动热力因子对“海棠”右侧中小尺度对流发展和维持起到重要作用,加剧了“海棠”非对称性结构,促使“海棠”强度维持不减。     

华东登陆热带气旋降水不同分布的对比分析

利用CMORPH降水资料，将热带气旋（TC）登陆后的降水分为路径左侧降水（L型）和右侧降水（R型）两类，并针对登陆华东地区TC的 L型和R型降水的大气环流场、环境水平风垂直切变以及台风环流内的动热力条件进行对比分析，结果表明:2005～2014年间登陆华东地区的20例TC中包括12例L型和8例R型。总体来看，大气环流因子对于登陆华东TC降水分布起主要作用。L型降水TC高层南亚高压主要呈纬向带状分布，在登陆过程中路径左侧维持偏东风高空辐散气流，中层西风槽偏东，西太平洋副热带高压（简称副高）偏南，环境水平风垂直切变指向西南。R型降水TC高层南亚高压断裂，呈经向分布。TC路径左侧风场较均匀，右侧东南风高空辐散气流明显。副高的位置偏北呈块状，同时环境水平风垂直切变指向东北，有利于路径右侧降水。台风环流内，低层冷暖平流输送以及水汽辐合与降水落区也有较好对应关系。L型TC低层暖平流的输送使TC西南象限低层增暖，大气稳定度降低。同时水汽辐合区也主要位于西南象限，有利于TC路径左侧降水。而R型TC副高位置偏北可将南侧的东南暖湿气流向台风环流更西部输送，东北象限维持暖平流，有利于路径右侧降水发生。     

Which Features of the SST Forcing Error Most Likely Disturb the Simulated Intensity of Tropical Cyclones?

Among all of the sources of tropical cyclone(TC) intensity forecast errors, the uncertainty of sea surface temperature(SST) has been shown to play a significant role. In the present study, we determine the SST forcing error that causes the largest simulation error of TC intensity during the entire simulation period by using the WRF model with time-dependent SST forcing. The SST forcing error is represented through the application of a nonlinear forcing singular vector(NFSV)structure. For the selected 12 TC cases, the NFSV-type SST forcing errors have a nearly coherent structure with positive(or negative) SST anomalies located along the track of TCs but are especially concentrated in a particular region. This particular region tends to occur during the specific period of the TCs life cycle when the TCs present relatively strong intensity, but are still intensifying just prior to the mature phase, especially within a TC state exhibiting a strong secondary circulation and very high inertial stability. The SST forcing errors located along the TC track during this time period are verified to have the strongest disturbing effect on TC intensity simulation. Physically, the strong inertial stability of TCs during this time period induces a strong response of the secondary circulation from diabatic heating errors induced by the SST forcing error. Consequently, this significantly influences the subsidence within the warm core in the eye region, which,in turn, leads to significant errors in TC intensity. This physical mechanism explains the formation of NSFV-type SST forcing errors. According to the sensitivity of the NFSV-type SST forcing errors, if one increases the density of SST observations along the TC track and assimilates them to the SST forcing field, the skill of TC intensity simulation generated by the WRF model could be greatly improved. However, this adjustment is most advantageous in improving simulation skill during the time period when TCs become strong but are still intensifying just prior to reaching full maturity. In light of this, the region along the TC track but in the time period of TC movement when the NFSV-type SST forcing errors occur may represent the sensitive area for targeting observation for SST forcing field associated with TC intensity simulation.     

The effect of surface friction on the development of tropical cyclones

When tropical cyclones (hereafter referred as TCs) are over the ocean, surface friction plays a dual role in the development of TCs. From the viewpoint of water vapor supply, frictional convergence and Ekman pumping provide a source of moisture for organized cumulus convection and is propitious to the spin-up of TCs. On the other hand, surface friction leads to a dissipation of kinetic energy that impedes the intensification of TCs. Which role is dominant in the developing stage of TCs is a controversial issue. In the present work, the influence of surface friction on the growth of TCs is re-examined in detail by conducting two sets of numerical experiments initialized with different cyclonic disturbances. Results indicate that, because of the inherent complexities of TCs, the impact of surface friction on the evolution of TCs can not be simply boiled down to being positive or negative. In the case that a TC starts from a low-level vortex with a warm core, surface friction and the resultant vertical motion makes an important contribution to the convection in the early developing stage of the TC by accelerating the build-up of convective available potential energy (CAPE) and ensuring moisture supply and the lifting of air parcels. This effect is so prominent that it dominates the friction-induced dissipation and makes surface friction a facilitative factor in the spin-up of the TC. However, for a TC formed from a mesoscale convective vortex (MCV) spawned in a long-lasting mesoscale convective system (MCS), the initial fields, and especially the low-level humidity and cold core, enable the prerequisites of convection (i.e., conditional instability, moisture, and lifting), to be easily achieved even without the help of boundary-layer pumping induced by surface friction. Accordingly, the reliance of the development of TCs on surface friction is not as heavy as that derived from a low-level vortex. The positive effect of surface friction on the development of TCs realized through facilitating favorable conditions for convection is nearly cancelled out by the friction-induced dissipation. However, as SST is enhanced in the latter case, the situation may be changed, and different development speeds may emerge between model TCs with and without surface friction considered. In short, owing to the fact that TC development is a complicated process affected by many factors such as initial perturbations, SST, etc., the importance of surface friction to the intensification of TCs may vary enormously from case to case.     

Environmental Influences on the Intensity Change of Tropical Cyclones in the Western North Pacific

The atmospheric and oceanic conditions are examined during different stages of the lifecycle of western North Pacific tropical cyclones (TCs), with the intention to understand how the environment affects the intensity change of TCs in this area. It is found that the intensification usually occurs when the underlying sea surface temperature (SST) is higher than 26℃. TCs usually experience a rapid intensification when the SST is higher than 27.5℃ while lower than 29.5℃. However, TCs decay or only maintain its intensity when the SST is lower than 26℃. The intensifying TCs usually experience a low-to-moderate vertical wind shear (2-10 ms-1 ). The larger the vertical wind shear, the slower the TCs strengthen. In addition, the convective available potential energy (CAPE) is much smaller in the developing stage than in the formation stage of TCs. For the rapidly intensifying TCs, the changes of SST, CAPE, and vertical wind shear are usually small, indicating that the rapid intensification of TCs occurs when the evolution of the environment is relatively slow.     

超强台风“威马逊”（1409）强度和降水特征及其近海急剧加强原因

利用常规观测资料以及海南省中尺度自动站资料、海口多普勒雷达产品、FY系列卫星云图和NECP 1°×1°再分析资料,分析了2014年第9号超强台风＂威马逊＂（1409）在海南岛登陆前后其强度和降水特征及其近海急剧加强的原因。结果表明：＂威马逊＂登陆海南省文昌市翁田镇时强度维持或略有减弱,登陆前其中心附近极大风速超过74 m·s-1,最低海平面气压899.2 h Pa,为1949年建国以来登陆我国大陆最强台风;＂威马逊＂从7月18日10时到当日15时登陆文昌前的5 h内,其中心附近最大风速增大了5 m·s-1,最低气压下降了20 h Pa,其超强台风量级从18日11时开始维持时间达17 h;＂威马逊＂眼壁回波造成的海南北部地区强降水具有降水效率高、对流发展不够强盛的混合性降水特征,而其螺旋雨带＂列车效应＂造成的海南西部地区极值降水则具有典型的对流性降水特征;西太平洋副热带高压、低空急流、西风槽和南亚高压是＂威马逊＂近海持续加强的主要影响系统;低层辐合与高层辐散、弱的环境风垂直切变和适宜的海面温度、深厚的暖涡是＂威马逊＂近海急剧加强的原因。     

The relationships between tropical cyclone tracks and local SST over the western North Pacific

Tropical Cyclone (TC) tracks over the western North Pacific (WNP) during 1949–2007, obtained from China Meteorological Administration/Shanghai Typhoon institute, are classified into three track types. These types are the main pathways by which TCs influence the coast of East Asia. The relationships between local sea surface temperature (SST) in WNP and TC tracks are revealed. Results show that the local SST plays an important role in TC tracks, though the relationships between local SST and the frequencies ...     

ENSO and Western North Pacific tropical cyclone activity simulated in a CGCM

A high-resolution (T213) coupled ocean–atmosphere general circulation model (CGCM) has been used to examine the relationship between El Niño/Southern Oscillation (ENSO) and tropical cyclone (TC) activity over the western North Pacific (WNP). The model simulates ENSO-like events similar to those observed, though the amplitude of the simulated Niño34 sea surface temperature (SST) anomaly is twice as large as observed. In El Niño (La Niña) years, the annual number of model TCs in the southeast quadrant of the WNP increases (decreases), while it decreases (increases) in the northwest quadrant. In spite of the significant difference in the mean genesis location of model TCs between El Niño and La Niña years, however, there is no significant simultaneous correlation between the annual number of model TCs over the entire WNP and model Niño34 SST anomalies. The annual number of model TCs, however, tends to decrease in the years following El Niño, relating to the development of anticyclonic circulation around the Philippine Sea in response to the SST anomalies in the central and eastern equatorial Pacific. Furthermore, it seems that the number of model TCs tends to increase in the years before El Niño. It is also shown that the number of TCs moving into the East Asia is fewer in October of El Niño years than La Niña years, related to the anomalous southward shift of mid-latitude westerlies, though no impact of ENSO on TC tracks is found in other months. It is found that model TCs have longer lifetimes due to the southeastward shift of mean TC genesis location in El Niño years than in La Niña years. As the result of longer fetch of TCs over warm SST, model TCs appear to be more intense in El Niño years. These relationships between ENSO and TC activity in the WNP are in good agreement with observational evidence, suggesting that a finer-resolution CGCM may become a powerful tool for understanding interannual variability of TC activity.     

台风强度模拟的海温目标观测研究

根据非线性强迫奇异向量(NFSV)型海温(SST)强迫误差识别的敏感性特征,通过观测系统模拟试验(OSSE)确定了12个热带气旋(TC)的强度模拟的海温目标观测最优布局.NFSV型SST强迫误差敏感区一般沿着台风移动路径,主要位于台风快速增强阶段.结果 表明,在NFSV型SST强迫目标观测敏感区内以90 km间隔加密海...     

Effects of a Dry-Mass Conserving Dynamical Core on the Simulation of Tropical Cyclones

The accurate forecasting of tropical cyclones(TCs) is a challenging task. The purpose of this study was to investigate the effects of a dry-mass conserving(DMC) hydrostatic global spectral dynamical core on TC simulation. Experiments were conducted with DMC and total(moist) mass conserving(TMC) dynamical cores. The TC forecast performance was first evaluated considering 20 TCs in the West Pacific region observed during the 2020 typhoon season. The impacts of the DMC dynamical core on forecasts o...     

EFFECT OF INITIAL PERTURBATION OF LAND SURFACE PROCESSES ON TROPICAL CYCLONE FORECAST

Many studies have explored the importance and influence of planetary boundary layer processes on tropical cyclones (TCs). However, few studies have focused on the influence of land surface processes on the activity of TCs. To test the effect of initial perturbations of land surface processes on TCs, a land surface process perturbation module is built in a global ensemble prediction system. Ensemble experiments for the TCs that occurred from 12 UTC 22 August to 18 UTC 24 November, 2006 show that consideration of the uncertainties within the land surface process could increase the predictability of the global ensemble prediction system. Detailed analysis on TC Xangsane (2006) indicates that the perturbation of land surface processes may increase the variation of sensible heat flux and latent heat flux. Meanwhile, the effect from land surface perturbation can be transferred to the upper atmosphere, which leads to better TC forecasts.     

Contribution of tropical cyclones to abnormal sea surface temperature warming in the Yellow Sea in December 2004

Unusual sea surface temperature (SST) warming occurred over the Yellow Sea (YS) in December 2004. To identify the causes of the abnormal SST warming, we conducted an analysis on atmospheric circulation anomalies induced by tropical cyclones (TCs) and their impacts on upper ocean characteristics using multiple datasets. With the analysis of various datasets, we explored a new aspect of the relationship between TC activity and SST. The results show that there is a significant link between TC activity over the Northwest Pacific (NWP) and SST in the YS. The integrated effect of consecutive TCs activity induces a large-scale atmospheric cyclonic circulation anomaly over the NWP and consequently anomalous easterly winds over the YS and East China Sea. The mechanism of the unusually warm SST in the YS can be explained by considering TCs acting as an important source of Ekman heat transport that results in substantial intrusion of relatively warm surface water into the YS interior. Furthermore, TC-related circulation anomalies contribute to the retention of the resulting warm SST anomalies in the entire YS.