西北太平洋夏季风的变化对台风生成的影响

研究了西北太平洋夏季风特征及其季风槽结构对台风生成的影响。当西北太平洋季风槽增强并向东扩展使季风加强时,西北太平洋的风速垂直切变、高低空辐散风、湿度和海温等都对台风的生成产生有利的影响,台风数明显比季风槽弱时多。而且对台风生成的位置也有很大的影响,即季风槽强时,台风的生成位置偏东,季风槽弱时台风的位置偏西。这表明西北太平洋夏季风主要是通过季风槽活动影响台风的生成。而夏季风的强弱对台风也有影响,在西北太平洋夏季风的活跃阶段,西北太平洋夏季风强时,台风生成的比较多,夏季风中断时台风生成的比较少。西北太平洋夏季风通过季风的季节内振荡对西北太平洋台风也有显著的影响。季节内振荡对台风生成的影响主要以30—60 d振荡为主。在这种低频振荡对流活动的湿位相时期台风生成个数明显多,干位相时期台风生成的少。而且低频振荡的西风位相也有利于台风生成,在东风位相时生成的台风少。另外,还研究了多台风期西北太平洋夏季的特征(群发性),发现在这些时期,存在强的季风槽,弱的垂直切变与充足的水汽供应。这表明西北太平洋台风时空的群发性与夏季风活动的异常密切相关。     

西北太平洋夏季风对中国长江流域夏季降水的影响

利用1979～2005年NCEP/NCAR的环流场再分析资料和降水资料, 通过对季风期降水、 大气环流、 水汽输送及低频振荡等方面的分析, 分别从时间和空间上分析了西北太平洋夏季风与中国长江流域夏季降水的联系。结果表明:(1) 西北太平洋夏季风与中国长江流域夏季降水存在显著的负相关关系, 在西北太平洋夏季风强盛时, 副热带高压异常偏北, 其西侧的偏南气流异常偏弱, 使得我国长江流域形成低层异常环流及水汽输送的辐散区, 从而造成长江流域夏季降水偏少; 而在西北太平洋夏季风减弱的年份, 西太平洋副高异常偏南偏西, 在长江流域以南地区形成异常偏强的偏南风水汽输送, 使得长江流域成为南、 北距平风的汇合区, 其上空对流活动异常活跃, 非常有利于长江流域的降水。 (2) 东亚局地Hadley垂直环流在强、 弱季风年也显著不同, 在强季风年里, Hadley局地环流异常偏弱, 长江流域上空出现的下沉运动距平, 使得该地区降水减弱, 而弱季风年则正好相反。 (3) 西北太平洋夏季风存在显著的气候平均的大气季节内振荡 (CISO), 在西北太平洋夏季风减弱时期, 长江流域降水同时受到源自热带西北太平洋西传CISO和源自热带印度洋东传CISO的共同影响, 可能造成了某种锁相关系, 从而造成降水偏多; 而在强季风年里长江流域只受由西太平洋西传的CISO的影响, 不容易激发降水。     

热带西北太平洋10~30 d振荡对南海夏季风影响

采用1958—2011年NCEP/NCAR再分析资料以及ERSST海温资料,分析热带西太平洋夏季对流10~30 d振荡对南海夏季风的影响。在年际变化尺度上,热带西北太平洋夏季10~30 d振荡强度指数 (TWPI) 与南海夏季风强度有很好的正相关关系。在TWPI增强年份,海温主要呈El Ni?o分布,南海周边区域增强的异常西风产生强的正涡度切变,导致异常气旋性环流,为季风槽的增强提供了热量和水汽,从而增强南海夏季风强度。反之,在TWPI减弱年份,海温主要呈La Ni?a分布,南海夏季风强度减弱。在不同的年代际背景下,垂直切变和水汽-对流的总体变化是影响TWPI总体变化的重要因子,但不能影响南海夏季风强度的总体变化。海陆热力对比的总体变化是导致南海夏季风强度总体变化的主要影响因素。     

热带MJO和ENSO对西北太平洋热带气旋影响研究综述

对西北太平洋热带气旋的活动规律作了综合评述,简单回顾了热带季节内振荡（MJO）特征和厄尔尼诺/南方涛动（ENSO）特征以及两者间关系,较系统地总结了近年来国内外学者关于MJO和ENSO对西北太平洋海域热带气旋活动影响和机理等方面的研究成果。讨论的热带气旋活动特征包括源地、频数、路径、强度、生命期和登陆等几个方面,并简单讨论了目前该领域存在的科学问题和未来可能的研究方向。     

西北太平洋SST季内振荡及其与中国东部夏季降水季内振荡的关系

利用NOAA逐日海表面温度(sea surface temperature,SST)资料、NCEP/NCAR逐日风场和比湿资料以及中国国家气象信息中心提供的逐日降水资料,研究了西北太平洋气候SST的低频周期,进一步分析了夏季西北太平洋SST季节内振荡与中国东部同期降水异常的关系。结果表明:夏季西北太平洋季节内SST异常影响中国东部同期季节内降水最显著的三个区域为:长江中游及华南沿海;江淮流域;华北大部。其影响途径主要是通过西北太平洋季节内海温与850 h Pa环流场之间相互作用,在东亚沿岸自南向北逐渐形成气旋—反气旋—气旋(反气旋—气旋—反气旋)的波列结构,引起东亚沿海局地水汽的辐合辐散,使得中国东部夏季季节内雨带从江淮流域向华北推进(从华北南撤到长江中游及华南沿海地区)。     

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。      

El Ni?o衰退年夏季西北太平洋异常反气旋季节内演变特征及其机制

基于多种再分析资料和观测资料,分析El Ni?o衰退年北半球夏季西北太平洋异常反气旋(NWPAC)季节内演变特征及其机制。结果表明,较之El Ni?o衰退年6月,NWPAC在7月与8月北移,且其强度在7月与8月显著增强。NWPAC通过影响对流层低层水汽通量散度对东亚夏季季节内降水产生影响,使东亚夏季异常雨带随NWPAC北移而逐渐北移;与NWPAC相伴随的降水异常减弱与入射太阳短波辐射增强,可引起夏季中南半岛、菲律宾及我国南部地区地表气温正异常,且随着NWPAC北移,东亚地表气温异常也随之北移。局地海气相互作用过程可能是NWPAC夏季季节内北移的成因之一。NWPAC北侧短波辐射的减弱和海表潜热与感热释放的增强会造成其下海温负异常,而海温负异常有利于NWPAC的维持。与之相反,NWPAC南侧短波辐射的增强与海表潜热与感热释放的减弱会造成其下海温正异常,而海温正异常可能会激发对流不利于NWPAC的维持。     

GAMIL1.0大气模式模拟的西北太平洋夏季风：阵风参数化方案的影响

本文分析了中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室( LASG/IAP)发展的大气环流格点模式(GAMIL1.0)对1980～1999年西北太平洋夏季风的模拟,讨论了阵风参数化方案对模拟效果的影响.结果表明:GAMIL1.0能合理再现西北太平洋夏季风气候态和年际变率的主要特征,不足之处在于其...     

亚洲夏季风爆发前后西北太平洋和孟加拉湾热带气旋活动统计特征

亚洲夏季风爆发始于孟加拉湾,然后向中国南海和印度次大陆扩展,其过程约持续1个月。各地区夏季风爆发时间呈明显的年际变化。利用热带气旋资料和气象再分析资料,统计了1951-2010年孟加拉湾和中国南海夏季风爆发前后西北太平洋热带气旋、孟加拉湾气旋风暴活动和夏季风爆发的关系。结果表明,在孟加拉湾夏季风爆发过程中,共有36 a出现孟加拉湾气旋风暴,并且夏季风爆发偏早年出现风暴的几率最高,为80%。在孟加拉湾夏季风爆发偏早、正常和偏晚3种类型中,孟加拉湾风暴活动频率高峰期多出现在夏季风爆发前后几天内。并且在孟加拉湾风暴活动频率高峰出现前期,西北太平洋热带气旋最先出现活动频率高峰。孟加拉湾夏季风爆发前有40%-50%的年份西北太平洋出现热带气旋活动,其中,夏季风爆发偏早年,爆发前西北太平洋热带气旋活跃的时间偏早（4月第2候）,且多活动在中国南海和菲律宾附近;爆发正常年,西北太平洋热带气旋活跃的时间为4月第4候,多活动在略偏东的海域;爆发偏晚年,西北太平洋热带气旋活跃的时间为5月初,活动区域最偏东。中国南海夏季风爆发过程中,60 a中共有29 a西北太平出现热带气旋,其中爆发偏早和正常年出现热带气旋的频率较高,并且热带气旋多出现在爆发当日和爆发后一段时间。整体来看,亚洲夏季风爆发前,西北太平洋热带气旋活动频率最先开始增强,然后孟加拉湾风暴开始活跃并伴随着孟加拉湾夏季风爆发,夏季风爆发偏早和正常年,孟加拉湾夏季风爆发后,西北太平洋热带气旋再次增强,中国南海夏季风爆发。      

热带季节内振荡对西北太平洋台风生成的大尺度环境的影响

基于澳大利亚气象局发布的RMM(Real-time Multivariate Madden-Julian oscillation)指数,将热带大气季节内振荡划分为8个位相,统计分析了各位相西北太平洋台风生成频数和位置的变化特征,并进一步利用BDI(Box Difference Index)指数分析了台风生成的活跃和不活跃位相之间环境要素的差别。结果表明,相比于台风生成的不活跃位相(1、2、3位相),在利于台风生成的活跃位相(5、6、7位相)期间,环境场具有更强的低层辐合和高层辐散外流、更高的对流层中层相对湿度和更广的垂直切变较小区域。进一步研究表明,在台风生成的活跃和不活跃位相之间,大尺度环境场的差别主要体现在动力因子方面,尤其是低层辐合场。     

IMPACT OF CONVECTION OVER THE SOUTH CHINA SEA ON TROPICAL CYCLONE MOTION OVER THE WESTERN NORTH PACIFIC DURING SUMMER MONSOON

The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows.(1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active(inactive), the SCS-WNP monsoon trough stretches eastward(retreats westward) due to the activity(inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward(stretches westward), which enhances(suppresses) the monsoon circulation.(2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases.(3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase.(4) Simulation results show that the steering flow associated with the active(inactive)phases is in favor of straight-moving(recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.     

THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE MID-LATITUDE WESTERN PACIFIC ON THE ASIAN SUMMER MONSOON

By Using the P-σ five-layer primitive equation model,three sets of numerical experiments are performedwith normal zonal mean SST(the control case),the positive SST anomalies in the Kuroshio current andeast-of-Japan Ocean(the midlatitude western Pacific),and positive SST anomalies over both the midlatitudeand the equatorial western Pacific.The experimental results show that the positive SST anomalies over themidlatitude western Pacific have great influence on the Asian summer monsoon:the Indian monsoon is weak-ened and the East Asian monsoon is intensified.This happens just reverse to the effects of positive SSTanomalies over the equatorial westero Pacific on the Asian summer monsoon.Further,the influence mechanismof the SST anomalies over the midlatitude westcrn Pacific on the Asian summer monsoon is discussed.     

南海夏季风演变的气候学特征

本文总结南海北部地区夏季风演变的气候学特征，发现南海地区５月第３候对流层高层东风和北风爆发，对流层低层西风第１次跃升，东亚经向季风环流圈开始形成，这可以成为南海地区夏季风爆发的标志。对流层低层西风在６月中旬开始的第２次连续跃升对应江淮地区的梅雨爆发期。类似地，中国大陆夏季对流层低层５月初和６月初有两次爆发性增暖过程，第２次比第１次强烈得多。南海北部地区对流层低层纬向风速、比湿盛夏呈双峰型，纬向风速峰值分别出现在６月第５候和８月第４候，比湿峰值分别出现在６月第６候和８月第５候。比湿突升对应纬向风速突升，但略落后于风速峰值出现的时间。南海北部地区季风爆发前，温度是波动式上升的，南海季风爆发后，温度是波动式下降的。中国大陆东部及南海地区夏季对流层低层比湿分布有３次突变，即４月中旬南海北部比湿突增，并开始出现高比湿中心，而南海南部为最大比湿中心；５月中旬最大比湿中心已从南海南部跳到了南海北部－华南并向江淮流域扩展；６月中旬江淮流域比湿突增并一直维持到８月，同时南海南部高比湿带消失。而５月中旬ＯＬＲ有一次突变，ＯＬＲ低值区爆发性向北扩张，这对应于南海地区夏季风的爆发。而孟加拉湾地区夏季风演变的气候学特征与南海地区有较     

印度夏季风的年代际变化与我国北方的气候跃变

利用NCEP／NCAR再分析资料及台站实测资料分析了近几十年印度夏季风的年代际变化特征及我国北方所发生的气候变化，揭示了印度夏季风的减弱与我国北方地区的气候演变具有密切的联系。分析结果表明：在1960年代中期和1970年代后期印度夏季风环流经历了两次明显的减弱过程，这两次减弱过程的出现与我国北方地区所发生的气候跃变在时间上十分接近；印度夏季风的年代际变化与北方地区(包括华北、东北、蒙古东部及朝鲜半岛)对流层温度变化存在显著的正相关关系，北方地区对流层温度的不断下降改变了海陆之间的热力对比，从而引起印度夏季风的减弱。     

GENERAL SITUATION ABOUT ACTIVITY OF SUMMER MONSOON OVER SOUTH CHINA SEA IN 2004 ASIAN SUMMER MONSOON INDEX

Based on daily NCEP reanalysis data, OLR and satellite rainfall data, the characteristic of the activities of South China Sea summer monsoon(SCSSM) in 2004 were analyzed. The results showed that the establishment of SCSSM was little later than normal and the intensity was stronger than normal. Influenced by the location of the northwest Pacific subtropical high, which was much northward and westward than normal, SCSSM was active mainly in the South China Sea areas. There existed obvious intraseasonal oscillation and two significant periods of SCSSM, one was about 20-30 days and the other about 40-50 days. The transportation of moisture was concentrated on the South China Sea and the northwest Pacific regions, reducing the northward transportation and resulting in drought in southern China     

ON THE PROCESS OF SUMMER MONSOON ONSET OVER EAST ASIA

Using daily observational rainfall data covered 194 stations of China from 1961 to 1995 andNCEP model analyzed pentad precipitation data of global grid point from 1979 to 1997,thedistribution of onset date of rainy season over Asian area from spring to summer is studied in thispaper.The analyzed results show that there exist two stages of rainy season onset over East Asianregion from spring to summer rainy season onset accompanying subtropical monsoon and tropicalmonsoon respectively.The former rain belt is mainly formed by the convergence of cold air and therecurred southwesterly flow from western part of subtropical high and westerly flow from the so-called western trough of subtropical region occurring during winter to spring over South Asia.Thelatter is formed in the process of subtropical monsoon rain belt over inshore regions of South ChinaSea originally coming from south of Changjiang (Yangtze) River Basin advancing with northwardshift of subtropical high after the onset of tropical monsoon over South China Sea.The pre-floodrainy season over South China region then came into mature period and the second peak of rainfallappeared.Meiyu,the rainy season over Changjiang-Huaihe River Basin and North China thenformed consequently.The process of summer tropical monsoon onset over South China Sea in 1998is also discussed in this paper.It indicated that the monsoon during summer tropical monsoononset over South China Sea is the result of the westerly flow over middle part of South China Sea,which is from the new generated cyclone formed in north subtropical high entering into SouthChina Sea,converged with the tropical southwesterly flow recurred by the intensified cross-equatorial flow.     

SIMULATION OF SUMMER MONSOON CLIMATE OVER EASTERN CHINA USING A REGIONAL SPECTRAL MODEL

In this paper, we evaluate the characteristics of the surface air temperature and the precipitation of summer monsoon, using the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) for 20 years (1984-2003). The RSM model was designated over the eastern China with a horizontal grid spacing of approximately 30 km. The model is driven by the NCEP/NCAR reanalysis data and runs from May 21 to September 1 for each of the 20 years. The distribution and variation patterns of the 20-year summer mean surface air temperature and precipitation are reproduced by the RSM and the differences between the simulation and observation are small. However, the model overestimates the interannual variability of summer precipitation in eastern China. The correlation coefficients of the 20-year averaging summer precipitation over the whole region and the sub-domains are above 0.8. The simulated probability distributions of daily maximum and minimum temperatures are similar to the observations. Days of different precipitation intensities in the simulations are generally consistent with the observations: the simulated days of light rain, moderate rain, heavy rain and torrential rain closely resemble the observations, but the simulated maximum centers of the distribution are north of the observed ones.     

NUMERICAL EXPERIMENTS ON THE FORMATION OF THE EASTERN PACIFIC SUMMER MONSOON

In this paper,we use a two-dimensional primary equation model which contains (1) heating ofradiation,(2) heating of condensation,and (3) transfers of sensible and latent heat between air andthe underlying surface.To investigate the causes for the formation of the eastern North Pacific sum-mer monsoon,the data at 110°W are obtained and winds at underlying surface and at 200 hPa aremodified under the conditions (1) removing topography and (2) changing meridional sea surface tem-perature (SST) gradient.In the numerical modification,we find that by removing the topography,the center's location ofthe eastern North Pacific summer monsoon does not change,but the intensity of the summer monsoonis weakened.Also the onset of the summer monsoon is delayed to the end of May.The tropical east-erly jet is weakened obviously,even changes to westerly wind.On the other hand,we find that theSST gradient along 110°W influences the eastern North Pacific summer monsoon distinctly.If theSST gradient is decreased,the center of the southwest wind near 12°N does not exist any more.theintensity of the whole summer monsoon becomes very weak and the circulation pattern of the summermonsoon also changes a lot.Finally,we indicate that both topography and meridional SST gradient play important roles inthe occurrence of the eastern North Pacific summer monsoon.The meridional SST gradient is themost important factor that triggers the summer monsoon and the topography along 110°W influencesthe intensity and the onset time of the summer monsoon there mostly.     

ENSO对亚洲夏季风异常和我国夏季降水的影响

首先对ＥＮＳＯ过程中亚洲夏季风环流的变化进行了诊断分析，结果表明在Ｅｌ Ｎｉｎｏ事件和ＬａＮｉｎａ事件中亚洲夏季风系统各成员均发生不同程度的变化，甚至出现相反的变异特征。其中，对我国东部地区夏季降水进行了ＥＯＦ分析，并在此基础上分析了赤道太平洋ＳＳ－ＴＡ对我国东部地区夏季降水影响的区域和程度，该影响与ＥＮＳＯ循环的发展阶段密切相关，且在长江中下游地区和华南地区最为显著。