T-TREC方法反演登陆中国台风风场结构

在传统的基于天气雷达反射率因子的相关方法跟踪回波运动(TREC)技术的基础上,本研究发展出适用于台风环流反演的T-TREC方法.同传统的TREC技术相比,T-TREC根据台风环流呈逆时针方向旋转的特征,利用雷达观测资料客观选取台风中心,选取扇形网格单元,在以台风中心为原点的极坐标系下进行逆时针方向同波追踪.同时,该方法也利用雷达径向风资料客观选取切向的搜索范围并建立风场相关矩阵,以减少主观设定搜索区域造成的误差.通过利用中国新一代天气雷达网(CINRAD WSR-98D)观测的登陆台风桑美(0608)资料对方法进行验证,结果表明T-TREC方法可以更加准确估计强台风环流,反演的径向风平均误差小于4 m/s.其中径向风信息的引入明显提高了反演风场精度,特别是改善了在眼墙区因回波结构较均匀造成的风场低估.当台风靠近陆地时,因地物回波以及台风环流与地形相瓦作用激发对流的影响,使得低层风场反演误差增加.文中也探讨了台风中心、搜索网格单元大小等因子对反演精度的影响,结果显示,反演结果对于中心定化比较敏感,中心位置偏移4 km将造成反演的径向风平均误差增加约10%.而搜索单元大小对反演结果影响和台风尺度相关,若台风尺度较小,则较小的搜索单元反演效果较好.     

夏季热带北大西洋海温异常对西北太平洋热带气旋生成的影响

利用1979—2012年西北太平洋热带气旋最佳路径资料,Hadley中心的海温资料和NCEP/NCAR再分析资料等,研究了夏季(6—10月)热带北大西洋海温异常与西北太平洋热带气旋(Tropical Cyclone,TC)生成的关系及其可能机制。结果表明,夏季热带北大西洋海温异常与同期西北太平洋TC生成频次之间存在显著的负相关关系。热带北大西洋海温的异常增暖可产生一对东—西向分布的偶极型低层异常环流,其中气旋性异常环流位于北大西洋/东太平洋地区,反气旋异常环流位于西北太平洋地区。该反气旋环流异常使得TC主要生成区的对流活动受到抑制、低层涡度正异常、中低层相对湿度负异常、中层下沉气流异常,这些动力/热力条件均不利于TC生成。此外,西北太平洋地区低层涡旋动能负异常,同时来自大尺度环流的涡旋动能的正压转换也受到抑制,不能为TC的生成和发展提供额外能量源。反之亦然。     

An Idealized Numerical Study of the Effects of Uniform Zonal Winds on Tropical Cyclogenesis

The effect of uniform zonal winds on tropical cyclone(TC)genesis is examined on a beta plane using an idealized mesoscale model.The simulation results show that uniform easterly and westerly flows are both favorable for TC genesis.However,uniform easterly flows result in a faster TC genesis rate compared with uniform westerly flows.It is found that faster TC genesis is associated with greater surface heat fluxes and convection during the early stage.The superposition of uniform easterly flows and the beta effect results in greater surface heat fluxes and convection around the TC center compared with uniform westerly flows.Meanwhile,TC genesis is closely associated with the size and intensity of a mid-level circulation.The joint greater convection induced by the easterly flows and beta effect results in enhancement of the vertical temperature gradient,which is associated with the intensification of mid-level circulation.The strong and compact mid-level circulation is more favorable for efficient conversion of latent heat energy to the kinetic energy of the lower-level cyclonic winds.Thus,uniform easterly flows are more favorable for TC genesis than uniform westerly flows.     

Synoptic controls of outer mesoscale convective systems with high impact rainfall in western north pacific tropical cyclones

The generality of our conceptual model of Outer Mesoscale Convective System (OMCS) formation in western North Pacific Tropical Cyclones (TCs) that was based on a case study of Typhoon Fengshen (2008) is examined with a data base of 80 OMCSs during 1999-2009. Formations of 41 “Intersection type (Itype)” OMCSs are similar to our conceptual model in that the key feature is an elongated moisture band in the northerly TC circulation that interacts with the southwest monsoon flow. Two subtypes of these I-type OMCSs are defined based on different formation locations relative to the TC center, and relative to the monsoon flow, that lead to either outward or more cyclonic propagation of the OMCSs. Twenty-five “Upstream type (U-type)” OMCSs form in a similar moisture band, but upstream of the intersection of the outer TC circulation with the monsoon flow. Another 12 “Monsoon type (Mtype)” OMCSs are different from our conceptual model as the formation locations are within the monsoon flow south to the confluence region of TC northerly circulation with the monsoon flow. In all of these OMCSs, the monsoon flow is an important contributor to their climatology and synoptic environment. Expanded conceptual models of where the threat of heavy rainfall associated with the four types of OMCSs may be expected are provided based on different OMCS formation locations relative to the TC center and different propagation vectors in a storm-relative coordinate system.     

Simulations of the motion of tropical cyclone-like vortices in the presence of synoptic and mesoscale circulations

Initial mesoscale vortex effects on the tropical cyclone(TC) motion in a system where three components coexist(i.e.,an environmental vortex(EV),a TC,and mesoscale vortices) were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically.Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases.However,they may have a more significant impact on the TC track under the following circumstances.First,the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region.This configuration may last for 8 h,and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion.Second,two mesoscale vortices located in the EV circulation may merge,and the merged vortex shifts into the EV inner region,intensifying both the EV and steering flow for the TC,increasing speed of the TC.     

Tropical Cyclone Energy Dispersion and Possible Self Maintenance Mechanism of the Synoptic Scale Wave Trains

The interaction between tropical cyclone (TC) and the large-scale mean flows such as the inter-tropical convergence zone (ITCZ) is investigated using a three-dimensional primitive equation model. Once a TC develops in the vicinity of the ITCZ region where satisfies both barotropic and baroclinic instabilities, the southeastward energy dispersion from the TC may disturb the ITCZ and thus help its breakdown. Cumulus convection can be organized in the region of cyclonic circulation, and the interaction between convective heating and the perturbation circulation may enhance the development of the waves, leading to the generation of a new tropical cyclone to the east. While the TC moves to the high latitude, the ITCZ will reform. Though repeating of this process, a synoptic-scale wave train oriented in the northwest-southeast direction can be generated and self-maintained. The results suggest that the mutual interaction among the low-frequency background flow, wave train pattern and TCs provides a possible mechanism for the origin of the summer synoptic scale wave train pattern over the western North Pacific.     

高原横切变线与高原低涡关系的初步研究

基于大气运动方程组及散度方程,对高原横切变线上扰动稳定性问题以及切变线诱发高原低涡的动力学机制进行了理论分析并用欧洲中心(ECMWF)ERA-interim再分析资料对其进行验证。得出高原横切变线是高原低涡产生的重要背景场,切变线以南的水汽输送与辐合对于低涡的诱发作用是大气处于不平衡状态而引起散度场调整的结果,辐合增强区有利于高原低涡生成,低涡中心对应非平衡正值中心,低涡外围为非平衡项负值区。非平衡项负值大值与水汽辐合带的重叠区对降水落区有较好的指示意义。当高原南部的西南风带向东或东北方向移动或当低涡下游出现非平衡项负值中心时,低涡亦同向移动。若高原出现气旋式环流并且环流中心与非平衡项正值中心对应时,有利于低涡生成;进一步,当低涡中心与非平衡项正值中心对应且正值中心数值不断增大时,低涡趋于发展加强。     

Beta gyres in global analysis fields

A three-component decomposition is applied to global analysis data to show the existence of a beta gyre, which causes Tropical Cyclone (TC) to drift from a large-scale environmental steering current. Analyses from the Global Data Assimilation and Prediction System (GDAPS) of the Korea Meteorological Administration (KMA), the Global Forecast System (GFS) of NCEP, and the Navy Operational Global Atmospheric Prediction System (NOGAPS) are used in this study. The structure of the beta gyre obtained in our analyses is in good agreement with the theoretical structure, with a cyclonic circulation to the southwest of the TC center, an anticyclonic circulation to the northeast, and a ventilation flow directed northwestward near the center. The circulation of the beta gyre is strongest at the 850-hPa level where the cyclonically swirling primary circulation is strongest, and decreases with height, in a pyramid shape similar to the primary circulation. The individual structure of the beta gyre is case- and model-dependent. At a certain analysis time, one model may clearly reveal a well-defined beta gyre, but the other models may not. Within one model, the beta gyre may be well defined at some analysis times, but not at other times. The structure of the beta gyre in the analysis field is determined by the nature of the vortex initialization scheme and the model behavior during the 6-h forecast in the operational data assimilation cycle.     

Potential vorticity diagnosis of tropical cyclone Usagi (2001) genesis induced by a mid-level vortex over the South China Sea

In this study, we first show that tropical cyclone (TC) Usagi evolved from a mid-level vortex over the South China Sea (SCS) in August 2001. The initial disturbance of TC Usagi had a maximum potential vorticity (PV) near 500 hPa, and an anticyclonic circulation with a cold core near the surface. The cyclonic circulation and its warm core of the mid-level vortex developed gradually downward toward the surface when environmental easterly and dry air intruded from the upper troposphere; finally, the mid-level vortex evolved into TC Usagi under favorable environment conditions such as weak vertical wind shear, deep moist layer, etc. To investigate the dynamic and thermodynamic processes during TC Usagi genesis, the technique of piecewise PV inversion is employed. The results show that the actions of upper-layer PV and potential temperature anomalies were not important in TC Usagi genesis. Surface-layer thermal anomalies mainly produced negative disturbances of temperature at the vortex center below 800 hPa, which was unfavorable to the genesis of a cyclonic circulation near the surface. Middle-to-lower-layer latent heat played a key role in TC Usagi genesis and downward development of dynamic and thermodynamic processes. The actions of dry air intrusion from the upper troposphere, environmental westerly changing into easterly in the middle and lower troposphere, and baroclinic structure of the vortex were also important. The cyclonic circulation of the mid-level vortex could develop downward quickly from the middle troposphere toward the surface. However, whether the warm core of the vortex developed near the surface depended on the combined actions of surface-layer thermal anomaly and middle-to-lower-layer latent heat. Finally, we present a conceptual model of TC Usagi genesis induced by a mid-level vortex over the SCS.     

Interannual horizontal heat advection in the surface mixed layer over the equatorial Pacific Ocean: assimilation versus TAO analysis

This study is motivated by an interest in obtaining a new automated classification scheme of daily circulation types suitable for use throughout Europe. The classification scheme is performed on 500 hPa geopotential height anomalies (NCEP Reanalysis data, 2.5°×2.5°). Nine grid points represent the study area. Five anticyclonic types (Anw, Ane, A, Asw and Ase) and seven cyclonic types (C, Cnnw, Cwnw, Cwsw, Cssw, Cse, Cne) are defined. Each of the circulation types has a distinct underlying synoptic pattern that produces the expected type and direction of flow over the study area. The classification scheme is applied to three different case studies in the Mediterranean Basin: Greece, Cyprus and central Italy. The precipitation percentage of the cyclonic type and the mean seasonal correlation coefficients for all circulation types are the two criteria used to evaluate the performance of the classification scheme. The ability of the HadAM3P general circulation model to reproduce the mean pattern and frequency of circulation types at the 500 hPa level in comparison to the NCEP dataset for the period 1960–1990 is also evaluated. The percentage of rainfall that corresponds to the cyclonic circulation types is greater than 85% for the three study regions. Furthermore, the correlation coefficients for the three classifications are very encouraging, for nearly all days of the study period. Compared to observations, the GCM is able to capture the mean patterns but not able to replicate exactly the observed variability of the circulation types over the three study regions.     

夏季亚洲-太平洋涛动与中国近海热带气旋活动的关系

采用联合台风警报中心的台风最伟路径资料和NCEP/NCAR再分析资料,分析了夏季亚洲-太平洋涛动(Asian-Pacif-ic Oscillation,简称APO)与东亚近海-西北太平洋大气环流的关系,并进一步探讨了APO与中国近海热带气旋(tropical cy-clone,简称TC)活动的关系.研究表明:(1)夏季APO强弱与同期西北太平洋及中国东部近海TC活动存在密切关系,即在APO强(弱)年,西北太平洋TC活动偏西(东)和偏北(南),中国东部近海TC明显增多(减少);(2)当APO偏强(弱)时,中国东部近海大气环流有(不)利于TC的维持和发展,表现为低层存在异常气旋性(反气旋性)环流,对流层高低层纬向风垂直切变减小(增大),且对流加强(减弱);(3)APO强弱也影响着TC引导气流的方向:在APO强(弱)年,西北太平洋副热带高压(以下简称副高)偏北和偏东(偏南和偏西),副高南侧偏东气流减弱(加强),有利于TC的向西北行或在偏北(南)纬度西行,进入中国东部近海的TC增多(减少);(4)APO强弱也影响着南海-热带西太平洋TC源地上空的大气环流,在APO强(弱)年,南海-热带西太平洋季风槽偏北、偏西(偏南、偏东),热带西太平洋TC活动偏北和偏西(偏南和偏东),有利于进入中国东部近海TC的增多(减少).     

Sensitivity of tropical cyclone intensification to inner-core structure

In this study, the dependence of tropical cyclone (TC) development on the inner-core structure of the parent vortex is examined using a pair of idealized numerical simulations. It is found that the radial profile of inner-core relative vorticity may have a great impact on its subsequent development. For a system with a larger inner-core relative vorticity/inertial stability, the conversion ratio of the diabatic heating to kinetic energy is greater. Furthermore, the behavior of the convective vorticity eddies is likely modulated by the system-scale circulation. For a parent vortex with a relatively higher inner-core vorticity and larger negative radial vorticity gradient, convective eddy formation and radially inward propagation is promoted through vorticity segregation. This provides a greater potential for these small-scale convective cells to self-organize into a mesoscale inner-core structure in the TC. In turn, convectively induced diabatic heating that is close to the center, along with higher inertial stability, efficiently enhances system-scale secondary circulation. This study provides a solid basis for further research into how the initial structure of a TC influences storm dynamics and thermodynamics.     

海表温度差异对1998及2016年8月西北太平洋热带气旋生成频数的影响

基于1970—2016年Hadley中心海温资料、NCEP/NCAR再分析资料和ECHAM4模式,研究了各海盆海表温度异常（SSTA）对1998和2016年这两个超级厄尔尼诺衰减年8月西北太平洋热带气旋（TC）生成及大尺度环流变化的可能影响。结果表明,热带印度洋和大西洋在1998与2016年几乎相反的SSTA型态是导致TC生成频数显著差异的主要原因之一,而热带和北太平洋SSTA在1998与2016年均分别在珠江三角洲和日本以南形成气旋性环流。1998年8月热带印度洋和大西洋SSTA产生的西北太平洋反气旋环流响应强于太平洋SSTA产生的气旋性环流异常,使西北太平洋受异常反气旋控制,减少TC的生成。2016年在三个大洋SSTA共同作用下,西北太平洋受异常气旋控制导致TC生成频数偏多。太平洋经向SSTA模在北半球副热带强迫出东西反向的跷跷板形势,在西北太平洋对流层产生的响应与实际变化相反,因此太平洋经向模对西北太平洋TC生成没有正的贡献。     

基于MTCSWA风场资料对西北太平洋热带气旋风场结构的气候统计特征研究

基于多平台热带气旋表面风场资料（MTCSWA）,研究了2007～2016年6～11月西北太平洋上不同尺度热带气旋（TC）的气候统计特征,TC各级风圈半径在不同象限的变化特征、风场结构的对称度及二者与强度变化之间的相关性。利用7级风圈半径与TC近中心最大持续风速（MSW）来定义TC的尺度和强度。结果表明,西北太平洋上TC的平均尺度为221.9 km,其中小TC平均尺度为96.4 km,大TC平均尺度为346.4 km。大TC活动位置的空间分布较小TC更为集中,整体活动范围较小TC偏北。TC尺度的峰值出现在8月和10月。在TC的风场结构中,7级、10级、12级风圈的平均半径分别为221.9、121.0、77.4 km。TC风圈的对称度的统计结果表明7级风圈的对称度最低,12级风圈的对称度最高。相关分析表明,在TC的生命史中,各级风圈半径与其强度存在一定的正相关关系,其中12级风圈半径与强度的相关性最低;对于同一风圈而言,在TC的不同发展阶段中,不同象限的风圈半径与强度的相关性不同。在TC的风场结构中,风圈的对称度与TC强度的相关性随着风圈强度的增强而减弱,只有7级风圈的对称度在TC的整个生命周期中表现出与TC强度之间的弱的正相关关系。     

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.     

AN INVESTIGATION INTO TROPICAL CYCLONE MOVING DIRECTION PREDICTION BASED ON OLR DATA

1 INTRODUCTION The Tropical Cyclone (TC) moving prediction is always difficult and important in operation. Though the numerical prediction and satellite data have contributed to the promotion of prediction capability in this way[1 – 3], it is not as satisfying for the unusual track of TC, and the primary reason is that the TC moving direction is influenced by many complicated factors. Therefore, further study of unusual TC motion using high-resolution satellite data is very important …     

Anomalous circulation patterns in association with two types of daily precipitation extremes over southeastern China during boreal summer

Based on the daily rainfall data from China Meteorological Administration, the tropical cyclone (TC) best track data from Japan Meteorological Agency, and the NCEP-NCAR reanalysis data from NOAA, regional mean daily precipitation extreme (RDPE) events over southeastern China (specifically, the Fujian-Jiangxi region (FJR)) and the associated circulation anomalies are investigated. For the summers of 1979–2011, a total of 105 RDPE events are identified, among which 35 are TC-influenced (TCIn-RDPE) and 70 are TC-free events (TCFr-RDPE). Distinct differences between these two types of RDPEs are found in both their statistical features and the related circulation patterns. TCFr-RDPEs usually occur in June, while TCIn-RDPEs mainly take place during July–August. When TCFr-RDPEs happen, a center of the anomalous cyclonic circulation is observed over the FJR, with an anomalous anticyclonic circulation to the south of this region. The warm/moist air flows from the South China Sea (SCS) and western Pacific meet with colder air from the north, forming a narrow convergent belt of water vapor over the FJR. Simultaneously, positive diabatic forcing anomalies are observed over the FJR, whereas negative anomalies appear over both its south and north sides, facilitating the formation and maintenance of the cyclonic circulation anomaly, as well as the upward motion of the atmosphere, over the FJR. When TCIn-RDPEs occur, southeastern China is dominated by a TC-related stronger anomalous cyclonic circulation. An anomalous anticyclonic circulation in the mid and high latitudes north of the FJR exists in the mid and upper troposphere, opposite to the situation during TCFr-RDPE events. Abundant warm/wet air is carried into the FJR from both the Indian Ocean and the SCS, leading to a large amount of latent heat release over the FJR and inducing strong ascending motion there. Furthermore, large differences are also found in the manifestation of Rossby wave energy propagation between these two types of RDPE events. The results of this study are helpful to deepen our understanding of the mechanisms behind these two types of RDPE events.     

西北太平洋热带气旋移动方向变化异常的环流特征

基于中国气象局和上海台风研究所整编的1972-2011年热带气旋(TC)best-track资料,采用极端天气气候事件定义的百分位法确定TC移动方向异常变化的阈值,利用Lanczos滤波法将大气环流分解成为季节内振荡(MJO)、准两周振荡(QBW)和天气3种尺度环流场,研究这3种尺度环流对热带气旋在南海地区异常北折的影响。结果表明:近40 a的资料统计显示,热带气旋12 h内移向逆时针方向偏转50°以及顺时针方向偏转47°为TC移动方向变化的95%分位数值,将12 h移动方向变化大于该数值的TC定义为移动方向变化异常。TC异常路径平均每年发生2.68次,9月份发生的概率最大,约为7%,最常发生在南海海域。分析3个发生在南海地区热带气旋异常北折的引导气流发现,在TC转向前,向西的引导气流纬向速度减慢,经向分量先向南加速,随后突然转为向北加速。天气尺度对应的引导气流对TC异常右偏影响最为明显,对流层中高层热带气旋中心东南侧强天气尺度西南气流引导TC异常右偏。     

热带气旋"蒲公英"两次登陆过程的灾害与结构特征

2004年7月1~3日,热带气旋“蒲公英”自生成到影响浙江沿海地区期间,不仅持续时间长、强度大,移动路径长、变化较复杂,而且创下了近3年来台湾风灾损失的最高纪录,同时也给浙江等沿海地区造成了一定的经济损失。作者主要利用卫星云图资料、NCEP再分析资料,从宏观上对热带气旋“蒲公英”两次登陆过程中的强度及其引发的风雨灾害进行了分析。结果表明,“蒲公英”登陆台湾期间,东亚环流形势呈典型的鞍形场分布,有利于处于两高之间热带气旋“蒲公英”的维持和北上转向。而在其登陆浙江沿海地区后,浙江沿海地区处于较强的偏东气流中,“蒲公英”中心处于高空槽后,气流下沉以及缺少水汽和能量充沛供应使得其减弱为热带风暴。无论是其登陆台湾还是浙江沿海地区,台风垂直方向始终呈深厚气旋性涡柱结构,但中心附近低层辐散,中层辐合,不利于中心附近的对流发展。相反,台风外围螺旋云带内不仅中低层辐合,高层辐散,辐合层较深厚,且存在高湿和强上升运动,因而有利于对流云团的发展。对流云团发展强度的不同使得“蒲公英”两次登陆期间引发的风雨灾害明显不同。     

应用雷达资料的临近预报方法对比试验

选取单部雷达的CAPPI资料,在TREC(Tracking Reflectivity Echo by Correlation)的基础上,引入径向基函数网络、广义回归网络、小波BP网络3种人工神经网络以及支持向量机,对雷达反射率因子进行1h的临近预报研究,并与TREC外推预报的结果进行了比较.使用了命中率、虚警率、漏报率、临界成功指数、相关系数和均方根误差6个指标检验人工神经网络、支持向量机和TREC的预报效果.结果表明:在使用这些指标检验预报效果时设定的阈值对预报结果的评价有影响;网络与TREC以及不同的网络之间的预报结果存在着差异;与TREC相比,支持向量机比TREC总体上能更好地预报未来1h以内强对流性天气的发展变化情况.