2008年西北太平洋热带气旋活动异常特征及成因分析

2008年西北太平洋热带气旋活动的特点:(1)初台异常偏早;(2)生成热带气旋异常偏少,但登陆热带气旋异常偏多,登陆热带气旋与生成热带气旋比例高;(3)从热带气旋的生成源地来看,2008年的热带气旋生成位置明显偏西.2008年热带气旋生成年频数异常偏少的主要原因:2008年仍处在生成热带气旋偏少的气候背景下,对流层低层...     

DYNAMIC FACTORS RELATED TO DECAY PROCESS OF OFFSHORE TROPICAL CYCLONES IN NORTHWEST PACIFIC

Intensity variation of tropical cyclones(TCs),especially that of coastal or landfalling TCs,is of great concern in current research.Most of the research papers,however,focus on intensification processes of TCs;only a few discuss decay processes in the lifetime of a TC.In the daily weather operation related to TCs,it is challenging when a TC weakens and/or disappears suddenly,because it brings more difficulties than the forecast of intensifying TCs does.Overestimation of a decaying landfalling TC would lead to over-preparation of defensive measures and result in"crying wolf"mentality with adverse effects.This study summarized physical mechanisms that dominate the decaying process of TCs and listed several possible dynamical factors:reduced level of air temperature,too large or too small speed,contraction of TC size amplification of TC’s core,and lightning number in a TC.     

APPLICATIONS OF THE CLOUDSAT TROPICAL CYCLONE PRODUCT IN ANALYZING THE VERTICAL STRUCTURE OF TROPICAL CYCLONES OVER THE WESTERN PACIFIC

Cloud profiling radar (CPR) onboard CloudSat allows for deep penetration into dense clouds/precipitation. In this study, tropical cyclones (TCs) are classified into three stages as developing, mature, and decaying. The circular TC area with the radius of 500 km is divided into five regions. The vertical structure characteristics of 94 Western Pacific TCs at different stages in different regions from June 2006 to February 2014 are statistically quantified using the CloudSat tropical cyclone overpass product (the CSTC Product). Contoured frequency by altitude diagrams (CFADs) of radar reflectivity show an arc-like feature and exhibit opposite distributions with a boundary at 5 km. Bright bands are found at this altitude, indicating melting layers. Deep convective (DC) clouds have the largest occurrence probability in the inner region, while Ci clouds occur more frequently in the outer region at 10-15 km. As clouds have the second largest vertical scale after DC clouds. Distributions of Ac, Cu, and Ns clouds at different stages have few distinctions. As the altitude increases, the ice effective radius and the distribution width parameter decrease while the particle number concentration increases. Moist static energy (MSE), cloud thickness (CT), liquid water path (LWP), ice water path (IWP), water vapor (WV), and rain rate (RR) all diminish along the radial direction and are significantly larger at the mature stage. The average value of MSE at the developing stage is larger than that at the decaying stage.     

SIMULATION OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC AND LANDFALLING IN CHINA BY REGCM4

This study evaluates the performance of the regional climate model RegCM4 in simulating tropical cyclone (TC) activities over the Western North Pacific (WNP) and their landfalling in China. The model is driven by ERA-Interim boundary conditions at a grid spacing of 25 km, with the simulation period as 1991–2010. Results show that RegCM4 performs well in capturing the main structural features of observed TCs, and in simulating the genesis number and annual cycle of the genesis. The model reproduces the general pattern of the observed TC tracks and occurrence frequency. However, significant underestimation of the occurrence frequency as well as the TC intensity is found. Number of the landfalling TCs over China is also much less than the observed. Bias of the model in reproducing the large-scale circulation pattern and steering flow may contribute to the underestimated landfalling TC numbers.     

西北太平洋双热带气旋相互作用统计分类及其特征分析

采用中国气象局与上海台风研究所提供的1949-2007年西北太平洋热带气旋最佳路径资料,统计分析了西北太平洋上的双(多)热带气旋相互作用现象.针对统计出的双热带气旋样本,根据相互作用两气旋的单独移动路径和它们相互作用的路径特征,归纳得到7种相互作用类型( A～G),并用聚类分析方法拟合得到每种类型的平均回归路径.分析讨...     

DIFFERENCES AMONG DIFFERENT DATABASES IN THE NUMBER OF TROPICAL CYCLONES FORMING OVER THE WESTERN NORTH PACIFIC

As shown in comparisons of the characteristics of inter-annual and inter-decadal variability and periodical changes in the number of tropical cyclones forming over the western North Pacific by three major forecast centers, i.e. China Meteorological Administration (CMA), Regional Specialized Meteorological Center of Tokyo (JMA) and Joint Typhoon Warning Center (JTWC) of Guam, there are the following important points. (1) Climatology of tropical cyclone (TC) or typhoon (TC on the intensity of TS or stronger) shows some difference in tropical cyclone frequency among the centers, which is more notable with TC than with typhoon. Both of them are more at the database of CMA than at those of the other two centers. (2) The difference is too significant to ignore in the inter-annual variability of tropical cyclone frequency between CMA and JTWC, which mainly results from the obvious difference in the inter-annual variability of the number of generated tropical depression (TD) between the two databases. The difference is small in the inter-annual variability of TS formations among all the three databases, and consistence is good between JMA and CMA or JTWC. (3) Though differences are not significant in the periodical variation of TC formations between CMA and JTWC, they are markedly apart in the inter-decadal variability, which is mainly shown by an anti-phase during the 1990s. (4) Non-homogeneity may exist around the late stage of the 1960s in the data of tropical cyclone frequency.     

IMPACT OF TROPICAL INTRASEASONAL OSCILLATION ON THE TRACKS OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

In this work,an index of tropical 20-90 d oscillation(intra-seasonal oscillation;ISO)in the western North Pacific(WNP)was determined via the combined empirical orthogonal function(EOF)method using daily outgoing longwave radiation(OLR)field data from the National Oceanic and Atmospheric Administration(NOAA),daily wind field data(at 850 hPa)from the European Centre for Medium-Range Weather Forecasts(ECMWF)and referencing the Madden-Julian oscillation(MJO)index proposed by Wheeler and Hendon.An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone(TC)tracks in the WNP during different ISO phases.The research results indicate that during the easterly phase of the ISO,under the impact of the northeastern airflow of anti-cyclonic ISO circulation,the easterly airflow south of the western Pacific subtropical high is relatively weak,and TCs generated in the subtropical high tend to change their tracks east of 140°E;during the westerly phase,there is a relatively high probability that TCs change their tracks west of 140°E.This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic(anti-cyclonic)circulation coincides with that of the cyclone.     

夏季季节内振荡对西北太平洋台风活动的影响

利用夏季季节内振荡(Boreal Summer Intraseasonal Oscillation, BSISO)指数和台风密集度分析了夏季季节内振荡和西北太平洋台风活动的关系。台风密集度定义为一天内500 km范围内台风出现的概率,与台风经纬度位置相比,台风密集度可更灵活地表达台风生成及移动特征。结果表明夏季季节内振荡对台风活动有明显的调制作用。当夏季季节内振荡指数1(BSISO1)处于第1、5、6、7、8位相时,南海及菲律宾以东海域台风活动明显增强;当夏季季节内振荡指数2(BSISO2)处于第2、3、4位相时,西北太平洋台风活动也明显增强。当夏季季节内振荡处于这些位相时,台风活动增强与南海及菲律宾以东海域环流气旋式异常、对流活动正异常相一致。      

ANALYSIS OF STRUCTURE EVOLUTION AND ENVIRONMENTAL CONDITIONS OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC DURING EXTRATROPICAL TRANSITION

Fifty-eight extratropical transition (ET) cases in the years 2000-2008, including 2,021 observations (at 6-hour intervals), over the western North Pacific are analyzed using the cyclone phase space (CPS) method, in an effort to get the characteristics of the structure evolution and environmental conditions of tropical cyclones (TCs) during ET over this area. Cluster analysis of the CPS dataset shows that strong TCs are more likely to undergo ET. ET begins with the increment of thermal asymmetry in TCs, along with the generation and intensification of an upper-level cold core, and ends with the occurrence of a lower-level cold core. ET lasts an average duration of about 28 hours. Dynamic composite analysis of the environmental field of different clusters shows that, in general, when TCs move northward, they are gradually embedded in the westerlies and gradually transform into extratropical cyclones under the influence of the mid- and higher-latitude baroclinic systems. As for those TCs which complete ET, there is always much greater potential vorticity gradient in the northwest of them and obvious water vapor transport channels in the environment.     

西北太平洋热带气旋移动路径的年际变化及其机理研究

利用JTWC的热带气旋资料、NCEP/NCAR再分析的风场资料以及Scripps海洋研究所的海温资料分析了西北太平洋热带气旋(TC)移动路径的年际变化及其机理。结果表明,西北太平洋TC移动路径有明显的年际变化并与西太平洋暖池热状态有很密切的关系。当西太平洋暖池处于暖状态,西北太平洋上空TC移动路径偏西,影响中国的台风个数偏多;相反,当西太平洋暖池处于冷状态,西北太平洋的TC移动路径偏东,影响日本的台风个数偏多,而影响中国的台风个数可能偏少。本研究以西太平洋暖池处于冷状态的2004年与西太平洋暖池处于暖状态的2006年的西北太平洋TC移动路径的差别进一步论证了这一分析结果并从动力理论方面分析了在西太平洋暖池不同热状态下,季风槽对赤道西传天气尺度的Rossby重力混合波转变成热带低压型波动(TD型波动)的影响,以此揭示西太平洋暖池的热状态对西北太平洋TC生成位置与移动路径年际变化的影响机理。分析结果表明,当西北太平洋暖池处于暖状态时,季风槽偏西,使得热带太平洋上空对流层低层Rossby重力混合波转变成TD型波动的位置也偏西,从而造成TC生成平均位置偏西,并易于出现西行路径;相反,当西太平洋暖池处于冷状态时,季风槽偏东,这造成了对流层低层Rossby重力混合波转变成TD型波动的区域,以及TC生成的平均位置都偏东,从而导致TC移动路径以东北转向为主。     

ANALYSIS OF TROPICAL CYCLONE PRECIPITATION FOR DIFFERENT INTENSITY CLASS IN NORTHWEST PACIFIC WITH TRMM DATA

Combined with TRMM products and Tropical Cyclone (TC) best track data in Northwest Pacific from 1 January 2003 to 31 December 2009, a total of 118 TCs, including 336 instantaneous TC precipitation observations are established as the TRMM TC database, and the database is stratified into four intensity classes according to the standard of TC intensity adopted by China Meteorological Administration (CMA): Severe Tropical Storm (STS), Typhoon (TY), Severe Typhoon (STY) and Super Typhoon (SuperTY). For each TC snapshot, the mean rainfall distribution is computed using 10-km annuli from the TC center to a 300-km radius, then the axisymmetric component of TC rainfall is represented by the radial distribution of the azimuthal mean rain rate; the mean rain rates, rain types occurrence and contribution proportion are computed for each TC intensity class; and the mean quadrantal distribution of rain rates along TCs motion is analyzed. The result shows that: (1) TCs mean rain rates increase with their intensity classes, and their radial distributions show single-peak characteristic gradually, and furthermore, the characteristics of rain rates occurrence and contribution proportion change from dual-peak to single-peak distribution, with the peak rain rate at about 5.0 mm/h; (2) Stratiform rain dominate the rain type in the analysis zone, while convective rain mainly occurred in the eye-wall region; (3) The values of mean rain rate in each quadrant along TCs motion are close to each other, relatively, the value in the right-rear quadrant is the smallest one.     

西北太平洋热带气旋迅速增强特征及其影响因子

选取西北太平洋上热带气旋(TC)24小时风速变化累积频率达95%所对应的15.4 m/s作为迅速增强(RI)的标准,研究了RI个例的基本特征以及TC自身特征因子与环境因子对RI的作用。结果表明,TC迅速增强过程的持续时间平均为33小时,最长可达78小时,并且TC经过迅速增强过程几乎都达到了台风级别以上,其中,一半以上达到了强台风级别以上。对比迅速增强(RI)和非迅速增强(non-RI)个例得到,RI个例相对于non-RI个例发生区域偏南偏东,两者的移动速度没有明显差异,但RI个例有较大向西移动分量并且前12小时增强较大;相对于non-RI个例,RI个例离最大潜在强度较远并且发生在较暖水区和55%～75%的低层相对湿度的条件下;RI个例发生在较小的垂直风切变和较弱的对流层上层东风气流情况下,由上层槽或冷低压引起的强迫弱于平均状况时RI较易发生。TC前12小时强度变化(DVMX)、海表面温度(SST)和垂直风切变(SHR)是影响迅速增强的主要因子,当DVMX≥6.3 m/s时RI发生的可能性最大,达到17.2%。当有若干个影响因子共同起作用时发生RI可能性显著增加,其中以较大的前12小时强度变化(DVMX≥6.3 m/s)、较高的海表面温度(SST≥29.4℃)、较弱的垂直风切变(SHR≤5.9 m/s)、较小的相对涡旋角动量通量辐合(REFC≤-1.6 m/(s.d))、偏东经度(LON≥138.2°E)和低纬度(LAT≤16.7°N)共同作用时,RI发生的可能性达到最大,可达66.7%。     

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.     

A CLIMATOLOGY OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

Based on best-track data and JRA-25 reanalysis, a climatology of western North Pacific extratropical transition (ET) of tropical cyclone (TC) is presented in this paper. It was found that 35% (318 out of 912) of all TCs underwent ET during 1979–2008. The warm-season (June through September) ETs account for 64% of all ET events with the most occurrence in September. The area 120°E–150°E and 20°N–40°N is the most favorable region for ET onsets in western North Pacific. The TCs experience ET at latitudes 30°N–40°N and have the greatest intensity in contrast to other latitude bands. The distribution of ET onset locations shows obviously meridional migration in different seasons. A cyclone phase space (CPS) method was used to analyze the TC evolution during ET. Except for some cases of abnormal ET at relatively high latitudes, typical phase evolution paths—along which TC firstly showed thermal asymmetry and an upper-level cold core and then lost its low-level warm core—can be used to describe the main features of ET processes in western North Pacific. Some seasonal variations of ET evolution paths in CPS were also found at low latitudes south of 15°N, which suggests different ET onset mechanisms there. Further composite analysis concluded that warm-season ETs have generally two types of evolutions, but only one type in cold season (October through next May). The first type of warm-season ETs has less baroclinicity due to long distance between the TC and upper-level mid-latitude system. However, significant interactions between a mid-latitude upper -level trough and TC, of either approaching or being absorbed into the trough, and TC’s relations with downstream and upstream upper-level jets, are the fingerprints for both a second type of warm-season ETs and almost all the cold-season ETs. For each type of ETs, detailed structural characteristics as well as precipitation distribution are illustrated by latitude.     

MEAN SQUARE DEVIATION ANALYSIS OF INTERANNUAL SST VARIABILITY IN TROPICAL PACIFIC AND INDIAN OCEAN

Using the SST data series in tropical ocean(20°N-20°S,50°E-80°W)during 1951-1997 to calculate its monthly mean square deviation,the work obtains results showing that interannual SST variability of the Pacific is more significant than that of the Indian Ocean.Especially near the central and eastern equatorial Pacific(165°W-90°W,6°N-6°S）。where it ranges from 2℃ to 4℃.The interannual SST variability is obvious in November and December but small in March and April.The interannual variabiltiy of “warm pool“SST is not so obvious as that of the eastern equatorial Pacific,Howerver,interannual SST variability of the Indian Ocean ranges from 1℃to 2℃ or so,being smaller than that of the Pacific,In the Indian ocean.Interannual SST variability of the Southern Hemisphere is more obvious than that of the Northern Hemisphere,According to above characterstics of interannual SST variability,the key sectors are determined.     

STUDY ON THE CHARACTERISTICS OF TROPICAL CYCLONES ACTIVITY OVER THE WESTERN NORTH PACIFIC IN 2004 AND THE CAUSATION

In this paper, we summarized the characteristics of tropical cyclones (TC) activity over the western North Pacific in 2004 and analyzed their causation. Compared with the normal, the annual frequency of TC in 2004 was slightly higher, tropical cyclones in 2004 had a longer life span and occurred in a concentrated period, the source of TC were situated eastward; in all tracks of TC, the recurvature tracks took up larger proportion, the landfall regions of TC were located northward, which concentrated from East China to Japan. The primary causes were revealed as follows. Firstly, the intensity and area of the western North Pacific subtropical high was stronger and larger than usual respectively, and its ridge was frequently in the form of cells and stretched northwestward. Secondly, the convergence of intertropical convergence zone (ITCZ) was reinforced and the convergence zone moved more eastward than average. Thirdly, the meridionality of the westerlies was larger than average and the cell-shaped ridge formed a saddle region, which is in favor of TC northward motion and recurature.     

南海-西北太平洋地区大气准双周振荡对TC生成的调节作用

通过对南海-西北太平洋地区大气10～20 d准双周振荡(QBWO)不同位相的划分(A～D),研究了QBWO对南海-西北太平洋海域热带气旋(TC)生成的调节作用。将TC分为强热带风暴及以下级别(TS)和台风及以上级别(TY),并将QBWO分为干湿位相,发现南海海域生成的TS(TY)在干湿位相的比与西北太平洋海域生成的TS(TY)在干湿位相的比相等,这表明QBWO对TS(TY)生成的调节作用在南海和西太平洋地区可能相同。从A位相到C位相,南海和西北太平洋地区TC的生成频数均逐渐增多,D位相时期,TC生成最少,多数TC发生在QBWO的对流活动湿位相,少数TC发生在干位相。南海-西北太平洋海域TC的生成受到QBWO的明显调制。从位相A到位相C,低频对流和低频风场逐渐向西北方向移动,低频对流强度持续加强,低频风场逐渐由异常西风-东风-西风转为异常东风-西风-东风配置,西北太平洋地区季风槽加强,使得TC生成频数逐渐增多。此外,在QBWO活跃位相,非绝热加热增强和纬向风垂直切变减弱也有利于TC的生成。     

热带太平洋和印度洋海温年际变化的均方差分析

运用1951～1997年热带（20°N～20°S,50°E～80°W）海温（SST）资料求出其各月的均方差,结果表明:太平洋海温变化相对印度洋海温变化要明显,特别是赤道中东太平洋附近 （165～90°W,6°N～6°S）的海温变化比较显著,其海温的变化范围在2～4°C左右,3～4月份海温年际变化小,11～12月海温年际变化大;“暖池”附近洋面海温年际变化也小。而印度洋海域的海温变化范围在1～2°C左右,在印度洋南半球洋面海温变化比北半球洋面海温变化相对较大。同时,根据上述海温变化特征确定了几个海温年际变化最大的关键区。     

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。     

影响我国热带气旋活动的气候特征及其与太平洋海温的关系

利用1956~2000年的热带气旋(简称TC,下同)资料对影响我国TC活动的气候特征进行了初步的统计分析,结果发现影响我国的TC活动具有明显的阶段性特征,1960年代影响我国的TC数明显偏少,而后进入偏多期,1990年代又相对偏少。影响我国的TC强度多集中于980~999 hPa,华东的闽、浙一带TC登陆比华南晚,但强度较大。在此基础上通过对影响我国的TC年个数与太平洋海温场进行相关分析,发现两个相关较密切的区域: 西太平洋暖池(120~150 E, 10~20 N)正相关区、赤道中东太平洋(180 ~90 W, 10 S~5 N)负相关区,这两个相关区具有较好的持续性。进一步分析影响我国的TC在El Ni駉年与La Ni馻年的气候特征发现,El Ni駉年影响我国的TC数较少,但强度较大,La Ni馻年则相反,影响我国TC多年和少年对应的太平洋海温距平分布形势分别与La Nia年和El Nio年的海温距平分布形势类似。