2010年和1998年西北太平洋热带气旋频数异常与东亚夏季风系统的关联性分析

利用西北太平洋编号台风资料、NCEP/NCAR再分析资料和NOAA向外长波辐射(outgoing longwave radiation,OLR)资料等,选取西北太平洋热带气旋频数异常偏少的2010年和1998年,诊断分析ENSO事件及其东亚夏季风环流异常与热带气旋频数异常的关系,给出东亚夏季风系统部分成员影响热带气旋频数的天气学图像:由春入夏,赤道东太平洋海温异常偏暖,赤道哈得来环流偏强,沃克环流偏弱;西太平洋副热带高压异常强大,位置偏西;季风槽位置偏南,东西向不发展;南海、西太平洋越赤道气流偏弱;异常热源和水汽汇偏南,南海和菲律宾以东地区对流活动受到抑制,热带对流活跃区位于赤道以南;热带气旋生成个数明显偏少,位置偏西。     

2005年夏季中国登陆台风的环流特征

利用NCEP/NCAR再分析资料和中国台风网提供的2005年台风资料，研究了2005年夏季台风登陆及中国东部频发性台风暴雨的环流特征及南北半球环流系统的相互作用。2005年夏季登陆我国的台风存在显著的阶段性变化，即6月10日～7月11日西太平洋无热带气旋生成，7月12日～9月30日西太平洋热带气旋频繁活动，造成登陆我国台风间隔时间短、 频数高、强度强，使得我国东部台风暴雨频繁发生。研究指出，6月10日～7月11日西太平洋无热带气旋生成与西太平洋副热带高压位置偏南、越赤道气流较弱、东亚热带辐合带（5°N～15°N，120°E～150°E）对流偏弱有关。而在7月12日～9月30日，西太平洋热带气旋活动频繁与西风槽的多次南下、西太平洋副热带高压断裂（或东撤）、东亚热带辐合带对流加强有关。进一步研究发现，气候平均态的西太平洋越赤道气流分别位于125°E和145°E附近， 2005年夏季125°E和145°E附近的越赤道气流减弱，然而在7月12日～9月30日，130°E～135°E附近的越赤道气流加强并维持时间较长。130°E～135°E附近越赤道气流加强与澳大利亚高压东移以及140°E～180 °E赤道低压加深有关。     

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。     

海洋和大气状态异常对西北太平洋台风活动的影响

本文分析了33年(1951—1983年)逐月平均的赤道东太平洋海温距平(SSTA)、热带西北太平洋500hPa高度距平和西北太平洋台风频数距平资料,指出:赤道东太平洋热力状况的异常对西北太平洋台风活动有明显影响。进一步对于1982—1983年的厄尼诺过程进行诊断分析,认为,SSTA异常可以通过经圈环流改变中、低纬环流的相互作用,以此来制约西北太平洋台风活动,即:当赤道东太平洋出现暖水时,北半球的哈得来环流加强,导致中纬度上空西风带加强、斜压扰动向南发展,结果,北半球副热带高压滞留在较低纬度、热带盛行东风气流,形成了不利于西北太平洋台风发生、发展的大尺度环流条件。     

2008年西北太平洋热带气旋活动特征分析

对2008年西北太平洋及我国南海热带气旋的活动特征进行总结,并从多方面分析其成因.结果指出:2008年西北太平洋热带气旋活动的主要特征为生成总数少,源地集中,位置偏西;登陆数多、时间早;登陆地点偏南、时间集中等.其原因主要在于:在热带气旋的多发期副热带高压面积偏大、强度偏强、西伸脊点异常偏西,且脊线偏南,造成西北太平洋热带地区盛行偏东风,不利于热带扰动的生成和发展;同时,也使得在其南侧生成的热带气旋易在偏东气流的引导下登陆我国南方.另外,季风槽、垂直风切变、海表温度和热带辐合带上的对流活动等因子的异常分布都不利于热带气旋在西北太平洋东部海域生成,直接导致这一年热带气旋生成总数明显偏少,源地显著偏西.     

越赤道气流准双周振荡对西北太平洋台风路径的调制作用

利用美国联合台风预警中心（Joint Typhoon Warning Center,JTWC）热带气旋（tropicalcy—clone,TC）数据、NCEP／NCAR再分析风场资料,研究了越赤道气流准双周振荡对西北太平洋台风路径的调制作用。将西北太平洋台风路径划分为：西行路径、西北行路径、转向登陆中国路径、转向中日之间路径、转向登陆日本路径、转向日本以东路径和140°E以东路径。利用超前滞后回归方法,合成分析了6—10月不同路径台风对应的越赤道气流准双周振荡的低频环流演变过程。结果表明,925hPa越赤道气流及与其相联系的经向风存在明显10～20d准双周振荡现象,且对西北太平洋台风路径预报具有一定的指示作用。在西太平洋赤道地区,低频越赤道气流强度、演变特征影响着西北太平洋低频气旋的位置和移动方向,调节风场强辐合带与季风槽的位置与强度,继而对台风生成位置、移动路径产生重要的影响。初步认为,强向北低频越赤道气流分量有利于北侧低频气旋加强和向北传播,继而使得强辐合带、季风槽位置偏北,台风易于在此区域生成且沿着强辐合带位置移动。而弱向北低频分量或向南低频分量则不利于台风转向移动。     

热带大气季节内振荡与对西北太平洋台风生成数的影响研究

用典型年合成方法分析研究了1979—2006年西北太平洋多台风年和少台风年热带大气ISO的影响。结果表明,热带大气ISO对西北太平洋台风的生成具有明显的调节作用。多台风年,菲律宾以西地区大气季节内振荡较弱,东传不明显;菲律宾以东地区积云对流较强,热带大气30～60 d低频振荡也偏强,与台风生成相关的传播特征为源自赤道140～160°E附近季节内振荡的西北方向传播。这种异常的30～60 d低频振荡对周围大气环流有正反馈的作用,从而导致积云对流的进一步加强,这种强的积云对流会引起赤道西风异常,产生异常Walker环流,在菲律宾附近形成风场的低层辐合、高层辐散,增强那里的上升气流,有利于台风生成。少台风年,菲律宾以西地区低频活动较强,东传明显,菲律宾以东的低频活动较弱。这种西强东弱的低频活动形式,使得大气低层在菲律宾以西地区为低频东风异常,菲律宾以东地区为低频西风异常,导致在菲律宾以东的西北太平洋大气产生低层低频风辐散、高层辐合的形势,增强下沉运动,不利于台风的生成。     

西北太平洋台风累积动能气候异常特征分析

应用美国联合台风警报中心(JTWC)提供的热带气旋数据、NCEP再分析资料和英国Hadly中心海表温度资料,分析了年台风累积动能(ACE)异常年气候特征及气候背景.结果表明:年台风累积动能有明显的年际和年代际变化;ACE异常年份由于季风槽东伸的经度、越赤道气流通道和强度以及副热带高压位置的显著差异,造成台风频数、强度和生命史的差异;当5-8月赤道中东太平洋海温为正距平、西南太平洋海温负距平时,通过异常沃克环流和局部哈得来环流的下沉支向西北太平洋输送跨赤道南风,导致该年西北太平洋ACE增多,反之该年ACE减少.     

7-9月登陆华南台风气候变化特征及大尺度环流系统分析

采用1949-2015年上海台风所提供的热带气旋资料、NCEP/NCAR全球再分析格点资料、国家气候中心提供的74项大气环流指数以及青藏高原积雪等资料,对7-9月登陆华南的热带气旋TC(不含热带低压)和台风TY(含台风及台风以上的热带气旋)的气候变化特征以及大尺度环流特征进行了分析,结果发现:7-9月登陆华南TC及TY频数均有微弱的上升趋势,且年际变化显著,但TC和TY年际变化和准十年波动变化并不总是一致,尤其是近10a来登陆华南的强台风有明显增加的趋势。7-9月登陆华南的TC占登陆中国的一半以上,并且有约3/4是来自西北太平洋生成的台风。从登陆华南TC的区间分布特征来看,以中路最多,西路次之,东路最少。亚洲季风偏弱、西太平洋副高偏西,登陆华南TY偏多,反之亦然。TC偏多(少)年,西太平洋副高偏强偏西(偏强偏东)。TC偏多年110oE以东引导气流出现的反气旋式和气旋式环流对较TC偏少年偏西,反气旋环流南部的东风异常一直延伸到华南地区东部,这样的东风引导气流异常有利于引导热带气旋登陆华南。另外,青藏高原东部和西部积雪偏多、华南气温偏高及西北太平洋海温异常偏暖的情况下也均有利于台风登陆华南。     

2004年西北太平洋热带气旋的活动特点与成因研究

对2004年台风汛期西北太平洋热带气旋的活动特点进行研究总结，进而对其成因做了分析。结果指出：2004年西北太平洋热带气旋主要特点是生成总数较常年略偏多，热带气旋生命史普遍较长、：生成时间相对集中、生成源地偏东，转向路径偏多，登陆气旋数多于常年平均值，登陆地段集中且偏北，集中在华东到日本一带。其成因在于：（1）副高面积偏大、强度偏强、位置偏北且西伸脊偏西，同时副高分布形态多呈块状，使得2004年台风的高频活动区向北偏移，直接对华东到日本一带造成威胁，乃至正面登陆影响；（2）澳大利亚高压强大，越赤道气流强，赤道辐合带辐合偏强、位置偏东，造成台风活动比较活跃且源地偏东；（3）西风带环流经向度较常年偏大而且副高多呈块状分布，东西两环副高之间形成的鞍型场有利于台风过此通道北上转向，导致转向台风偏多。     

THE EFFECT OF WARM POOL THERMAL STATES ON TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

The influence of thermal states in the warm pool on tropical cyclones (TCs) in the western North Pacific (WNP) is investigated. There are fewer typhoons during warm years of the warm pool in which tropical storms tend to form in the northwest quadrant and move westward. Inversely, typhoons tend to recurve northeastward to the southeast of Japan and increase in number in the southeast quadrant during cold years. Based on composite analyses, circulation-induced dynamic factors rather than thermal factors are identified as being responsible for TCs activities. During the warm state, the monsoon trough retreats westwards, which leads to anomalous vorticity in low-level and divergence in high-level in the western part of west Pacific. Above-normal TCs activity is found in this area. Furthermore, wind anomalies at 500 hPa determine the main track types. On the contrary, when the warm pool is in cold state, the atmospheric circulation is responsible for the formation of more TCs in the southeast quadrant and recurving track.     

RESEARCH ON THE INTERANNUAL AND INTERDECADAL VARIABILITIES OF THE MONSOON TROUGH AND THEIR IMPACTS ON TROPICAL CYCLONE GENESIS OVER THE WESTERN NORTH PACIFIC OCEAN

In this paper, we mainly summarize and review the progresses in recent climatological studies (by CMSR, IAP/CAS and some associated domestic and international institutions) on the interannual and interdecadal variabilities of monsoon troughs and their impacts on tropical cyclones and typhoons (TCs) geneses over the western North Pacific Ocean. The climatological characteristics of monsoon troughs and four types of circulation patterns favorable to TCs genesis over the western North Pacific Ocean in summer and autumn are given in this paper. It is also shown in this paper that the monsoon trough over the western North Pacific Ocean has obvious interannual and interdecadal variabilities. Especially, it is revealed in this paper that the interannual and interdecadal variabilities of the monsoon trough over the western North Pacific Ocean influence the TCs genesis not only through the impact on distributions of the vorticity in the lower troposphere and the divergence in the upper troposphere, the water vapor in the mid- and lower troposphere and the vertical shear of wind fields between the upper and lower troposphere over the western North Pacific Ocean, but also through the dynamical effects of the transition between convectively coupled tropical waves and providing disturbance energy. Besides, some climatological problems associated with TCs activity over the western North Pacific Ocean that need to be studied further are also pointed out in this paper.     

NUMERICAL SIMULATIONS OF THE PACIFIC MERIDIONAL MODE IMPACTS ON TROPICAL CYCLONES ACTIVITY OVER THE WESTERN NORTH PACIFIC

Based on analyses of the relationship between Pacific Meridional Mode (PMM) and number of tropical cyclones (TCs) activity over the western North Pacific, the impacts of the PMM on Tc activity over the western North Pacific are studied using numerical simulations with an Atmospheric General Circulation Model (CAM3) of National Center for Atmospheric Research (of USA). The result shows that the PMM has impacts on the large-scale generating environment of TCs, thus affecting their number and strength. The numerical simulations using the NCAR CAM3 indicate that with the inclusion of the forcing from sea surface temperature (SST) of the PMM, there appears a decreased magnitude of the vertical zonal wind shear, large proportion of relative humidity, anomalous westerly wind at low levels and anomalous easterly wind at high levels, in association with anomalous cyclonic circulation at low levels and anomalous anti-cyclonic circulation at high levels over the tropical western Pacific. Thus, the PMM provides favorable environment for the typhoon genesis. In the sensitivity experiment, TCs have larger strength, lower SST at the center, stronger tangential wind at 850 hPa and intensified warm cores at high levels. In this paper, the simulation results are similar to that in the data analyses, which reveals the important impact of the PMM on TC activity over the western North Pacific.     

STATISTICAL CLASSIFICATION AND CHARACTERISTICS ANALYSIS OF BINARY TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC OCEAN SUMMER: CONTRASTIVE ANALYSIS FOR ACTIVE AND INACTIVE YEARS OF TROPICAL CYCLONES

Using the 1949-2007 western North Pacific tropical cyclones (TCs) best-track data archived at the Shanghai Typhoon Institute of China Meteorological Administration for the western North Pacific from 1949 to 2007,both the characteristics of binary and multiple TCs and samples of interactions among TCs and multi-TCs are identified and statistically analyzed.According to the various features of individual TC tracks and interacting tracks,seven distinct types are proposed to describe the binary system of TCs and their interaction samples.The mean trajectories of the west and east component of binary TCs in each type are obtained using a new cluster analysis technique.These types are then analyzed in terms of landfall process,occurrence seasonality,coexistent lifetime,especially the large-scale patterns of atmospheric circulation.Finally,typical steering flows and conceptual models of the binary TCs at different phases are established based on six-hourly flow maps of the binary system and the averages are determined of the mean steering flow of ten representative binary TCs.Then,typical steering flows and conceptual models at the beginning,middle and final phase in each type are established to describe the large-scale circulation patterns of the binary system interaction types.     

ANALYSIS OF THE CLIMATIC CHARACTERISTICS OF LANDING TROPICAL CYCLONES IN EAST CHINA

The intensity, landing time, track trend and intensity variation of tropical cyclones (TCs) after landfall are analyzed using the TCs data (of best track from the China Meteorological Administration) between 1949 and 2006 for the western North Pacific and South China Sea. The trend differences of track and intensity between the TCs that directly land in East China and those making the second landfall in East China after landing in Taiwan Island are categorically discussed. The results show that the first kind of landing TCs are more likely to go northward or turn while the second kind of TCs have a larger tendency to keep going northwest. The intensity of the first kind of TCs is more persistent than the second one. There is a higher percentage for the intensity to be weakened significantly if the TCs keep going west to northwest or southwest after landing.     

IMPACT OF LARGE-SCALE CIRCULATION ON THE INTERDECADAL VARIATIONS OF THE WESTERN NORTH PACIFIC TROPICAL CYCLONE

Based on the annual frequency data of tropical cyclones from 1960 to 2005 and by the polynomial fit and statistical analysis, this work has discovered that TC activity in the 46a exhibits significant decadal- scale variability. It has two high frequency periods (HFP) and two low frequency periods (LFP). Significant differences in the number of TCs between HFP and LFP are found in active TC seasons from July to October. Differences of large-scale circulation during HFP and LFP have been investigated with NCEP/NOAA data for the season. In HFP, the condition includes not only higher sea surface temperature,lower sea level pressure, larger divergence of upper air, larger relative vorticity at low levels and smaller vertical shear, but also 500-hPa wind vector being more available for TC activity and moving to western North Pacific, the position of the subtropical anticyclone over the western Pacific shifting more northward,and South Asian Anticyclone at 100-hPa being much smaller than that in LFP. The precipitation of western North Pacific has no clear influence on TC activity.     

AN ANALYSIS ON INTERDECADAL VARIATIONS OF TROPICAL CYCLONE PRECIPITATION IN GUANGDONG PROVINCE OF CHINA

The interdecadal variations of tropical cyclones(TCs) and their precipitation over Guangdong Province are investigated using the observational data of TCs and precipitation from 26 observational stations in the province from 1951 to 2005.The results show that the TCs precipitation shows an oscillation with a peak value of about 25 years,with both the numbers of the Guangdong-influencing TCs and TCs formed in the western North Pacific oscillating with a peak value of about 23 years.The correlations are highly positive between the interdecadal variation of TC precipitation over the province and these numbers.The interdecadal variation of TC precipitation in the province shows significant negative correlations with the interdecadal variation of annual mean SST in some parts of the western North Pacific and the interdecadal variation of annual mean 500 hPa geopotential heights in some parts of the middle and high latitudes over the North Pacific.In general,there are high mean SSTs on the equator from central to eastern Pacific,low mean SSTs in the middle and high latitudes over the North Pacific and a main strong East Asian trough over the North Pacific in the period of less TC precipitation as compared with the period of more TC precipitation over the province.     

登陆华东热带气旋的气候特征分析

利用1949—2006年西北太平洋及南海的热带气旋（TC）资料,分析了登陆我国的TC强度、登陆时间、登陆后路径趋向及强度变化等气候特征,并重点讨论了直接登陆华东和登陆台湾后再次登陆华东的TC路径和强度趋势差异。结果表明,直接登陆华东的TC比登陆台湾后再次登陆华东（以下简称为间接登陆）的TC更易北上或北上转向,而间接登陆的TC更易维持西偏北行;另外直接登陆华东的TC登陆后的强度更易维持,其登陆后路径趋向在西北偏西和西南方位的强度明显减弱的百分比率比其它方位的大。      

西太平洋暖池对西北太平洋季风槽和台风活动影响过程及其机理的最近研究进展

本文回顾和综述了近年来关于西太平洋暖池对西北太平洋热带气旋和台风（TCs）活动影响过程及其机理的研究进展。文中首先简单回顾了近年来关于西太平洋暖池热状态和菲律宾周围对流活动变化特征及其对与TCs活动有关的南海夏季风爆发和西太平洋副热带高压的季节内、年际变异的影响过程和机理的研究;然后,本文系统地回顾了近年来关于西太平洋暖池热状态通过西北太平洋季风槽影响TCs活动年际和年代际变化的影响过程及其机理的研究。此外,文中还指出了关于西太平洋暖池对西北太平洋上空季风槽和TCs活动变异的热力和动力作用需进一步深入研究的科学问题。     

IMPACTS OF DIFFERENT KINDS OF ENSO ON LANDFALLING TROPICAL CYCLONES IN CHINA

Interannual variability of landfalling tropical cyclones(TCs) in China during 1960-2010 is investigated.By using the method of partial least squares regression(PLS-regression),canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs.El Ni o Modoki years are associated with a greater-than-average frequency of landfalling TCs in China,but reversed in canonical El Ni o years.Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Ni o phases occurs dominantly in the northern tropical western North Pacific(WNP).The patterns of low-level circulation anomalies and outgoing longwave radiation(OLR) anomalies associated with landfalling TC genesis with different types of El Ni o phases are examined.During canonical El Ni o years,a broad zonal band of positive OLR anomalies dominates the tropical WNP,while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics.In El Ni o Modoki years,a vast region of negative OLR anomalies,roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP,provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Ni o years.For more landfalling TCs formed in the northern tropical WNP in El Ni o Modoki years,there are more TCs making landfall on the northern coast of China in El Ni o Modoki years than in canonical El Ni o years.The number of landfalling TCs is slightly above normal in canonical La Ni a years.Enhanced convection is found in the South China Sea(SCS) and the west of the tropical WNP,which results in landfalling TCs forming more westward in canonical La Ni a years.During La Ni a Modoki years,the landfalling TC frequency are below normal,owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N.Since the western North Pacific subtropical high(WNPSH) in La Ni a Modoki years is located in the westernmost region,TCs mainly make landfall on the south coast of China.