Interactions between the 30–60 day oscillation,the walker circulation and the convective activities in the tropical western pacific and their relations to the interannual oscillation

In this paper, interactions between the 30-60 day oscillation, the Walker circulation and the convective activities in the tropical western Pacific during the Northern Hemisphere summer are analyzed by using the observed data of wind fields and high-cloud amounts for the period from 1980 to 1989.The analyzed results show that the 30-60 day oscillation (hereafter called LFO) may be largely affected by the convective activities in the tropical western Pacific. The LFO in the tropical western Pacific during the strong convective activities around the Philippines stronger than those during the weak convective activities around the Philippines. Moreover, in the case of strong convective activities around the Philippines, the LFO in the tropical west-ern Pacific and tropical eastern Indian Ocean generally propagates westward, and it is intensified by the LFO with a westward propagating center of maximum oscillation from the east to 140oE. However, in the case of weak convective activities around the Philippines, the LFO gradually becomes stronger with a eastward propagating center of maximum oscillation from the eastern Indian Ocean to the tropical western Pacific.Corresponding to the 30-60 day oscillation, the Walker circulation is also in oscillation over the tropical Pacific and its circulation cell seems to shift gradually westward from the tropical western Pacific to the tropical eastern In-dian Ocean with strong convective activities around the Philippines. This may maintain the intensification of convective activities there. However, during the weak convective activities around the Philippines, the Walker circula-tion gradually moves eastward and an ascending flow may appear in the equatorial central Pacific. This may cause convective activities to be intensified over the equatorial central Pacific.The analyzed results also show that the LFO in the tropical western Pacific and East Asia may be associated with the interannual oscillation of the SST anomaly in the tropical western Pacific.     

南亚高压季节内变化与热带季节内振荡之间的关系

采用观测分析和数值试验等方法,分析夏季南亚高压与热带季节内振荡(ISO)之间的关系,并对两者之间的相互作用进行量化诊断,探讨其物理过程.主要结果表明:南亚高压ISO与热带ISO活动关系密切,当热带ISO处于印度洋位相(第1、2、3位相),则南亚高压东脊点位置偏西,当ISO处于太平洋位相(第5、6、7位相),则南亚高压东...     

两类El Niño型对西北太平洋季风槽及热带气旋生成的可能影响

通过对1948~2015年不同El Ni?o事件下西北太平洋季风槽变化和热带气旋(tropical cyclone,TC)生成进行分析,初步探讨了不同El Ni?o型事件对季风槽及其对TC的可能影响。分析结果表明,较东太平洋增暖(eastern Pacific warming,EPW)年,中太平洋增暖(central Pacific warming,CPW)年季风槽偏弱,位置相对偏西、偏北。在CPW年,中(西和东)太平洋海温增暖(降低)引起了从中到西太平洋热带地区的西风异常和中太平洋地区上升运动及对流活动加强,使得季风槽加强东伸,同时西太平洋副高偏弱、偏北,季风槽向北推进;而在EPW年,赤道东(西)太平洋海温增暖(降低)使得赤道地区西风异常显著加强东扩,异常Walker环流的上升支东移至东太平洋,季风活动加强,副高偏强、偏南,这使得季风槽较CPW年相比更强、更偏东。利于TC生成的大尺度环境因子随季风槽强度和位置的变化而发生改变,在CPW年,低层气旋性涡度、高层辐散、高的中层相对湿度以及低垂直风切变区随着季风槽向北移动;而在EPW年,这些因子随季风槽向南、向东偏移。这些大尺度环境因子的变化使得西北太平洋TC生成的位置在CPW年比EPW年更加偏北、偏西。     

厄尼诺现象对热带大气环流影响的研究

应用NMC 17年热带格点风及OLR资料，对比分析了厄尼诺年与反厄尼诺年热带环流的差异，发现厄尼诺现象使多年平均位于西太平洋上的最强盛的对流加热区东移到中太平洋，太平洋热带地区东西向对流加热梯度减弱，造成中东太平洋上的Walker环流及西太平洋与印度洋上的反Walker环流场比常年减弱；同时，厄尼诺现象也使中东太平洋地区经向反Hadley环流及美洲大陆上空的Hadley环流减弱。     

冬/夏季热带太平洋与印度洋海表温度年际异常关系的年代际变化

利用NCEP/NCAR再分析资料、全球海温海冰GISST 2.3b资料, 用EOF技术分析了热带太平洋海表温度的年际异常 (SSTA) 变化特征表明:可用Ni?o3指数表示热带太平洋SSTA, 并用该指数来讨论热带太平洋、热带印度洋SSTA间的关系。分季节分析表明:冬季Ni?o3指数与热带印度洋SSTA间的关系表现为热带印度洋整体相关系数为正的单极形态, 且1976年以后两者的关系减弱, 其原因是冬季为ENSO事件的盛期, 另外, 冬季西太平洋暖水区东移导致太平洋Walker环流上升支强盛处的东移, 造成两洋的垂直纬向环流耦合减弱。夏季两者关系表现为偶极形态 (热带西印度洋与Ni?o3指数同相变化, 热带东印度洋则相反), 但1976年以后两者的关系有所加强, 是因为夏季为偶极子盛期, 也是ENSO事件的发展期, 同时夏季西太平洋暖水区东移并未引起太平洋Walker环流上升支强盛处的明显东移, 且印度洋季风环流、太平洋Walker环流的上升支强盛处的强度增大了, 造成两洋的垂直纬向环流耦合更强烈。即1976年以后, 冬季热带两洋SSTA间的关系减弱了, 而夏季两者关系则变得更密切。     

印度洋海温年际异常与热带夏季季节内振荡的关系及其数值模拟研究

利用观测分析资料和SINTEX-F海气耦合长时间(70年)数值模拟结果,分析了印度洋海温年际异常与热带夏季季节内振荡(BSISO)各种传播模态之间关系及其物理过程。结果表明,印度洋海温年际异常与热带BSISO关系密切,当印度洋为正(负)偶极子情况,中东印度洋北传BSISO减弱(加强);当印度洋为正(负)海盆异常(BWA)情况,印度洋西太平洋赤道地区(40°E -180°)东传BSISO加强(减弱)。印度洋海温年际变化通过大气环流背景场和BSISO结构影响热带BSISO不同传播模态强度的年际变化。在负(正)偶极子年夏季,由于对流层大气垂直东风切变加强(减弱),对流扰动北侧的正压涡度、边界层水汽辐合加强更明显(不明显),导致形成BSISO较强(弱)的经向不对称结构,因此北传BSISO偏强(减弱)。印度洋BWA模态通过影响赤道西风背景以及海气界面热力交换,导致赤道东传BSISO强度产生变化。在正BWA年夏季,赤道地区西风较明显,当季节内振荡叠加在这种西风背景下,扰动中心的东侧(西侧)风速减弱(加强)更明显,海面蒸发及蒸发潜热减弱(加强)更明显,导致扰动中心的东侧(西侧)海温升高(降低)幅度更大,从而使边界层产生辐合(辐散)更强、水汽更多(少),因此赤道东传BSISO偏强;而在负BWA年,赤道地区西风背景减弱,以上物理过程受削弱使赤道东传BSISO偏弱。     

对1972年厄尼诺过程中印度洋和太平洋赤道地区风场变化的分析

1972—1973年发生了一次强厄尼诺过程。已有不少人对这次厄尼诺过程中海洋要素和气象要素的变化进行了分析。这些讨论均将范围局限于太平洋地区。本文利用了COADS资料,对印度洋、太平洋赤道地区风场和海温场的变化作了综合分析,井对它们的变化与厄尼诺的关系进行了讨论。     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。      

Possible Linkage Between Tropical Indian Ocean SST Anomalies and the Date ofFirst and Last Tropical Cyclones Landfalling in the Chinese Mainland

Bases on the NCEP/NCAR reanalysis products, Had ISST dataset, and data of tropical cyclone(TC)landfalling in the Chinese mainland during 1960-2019, the possible impacts of Indian Ocean Dipole(IOD) mode and Indian Ocean basin(IOB) mode on the last-TC-landfall date(LLD) and first-TC-landfall date(FLD), respectively, are investigated in this study. The LLD is in significantly negative correlation with autumn IOD on the interannual timescale and their association is independent of El Nino-Southern O...     

热带太平洋-印度洋海温联合模及其气候影响

本文基于观测资料和LICOM2.0模拟结果的分析研究,简要介绍讨论了太平洋—印度洋海温(异常)联合模(PIOAM)的存在、特征、演变及其影响等问题。热带太平洋—印度洋区域乃至全球范围的海表温度异常(SSTA)资料进行EOF分解,都清楚表明其第一分量在热带太平洋—印度洋的空间形态与太平洋—印度洋海温(异常)联合模(PIOAM)非常相似,说明PIOAM是热带太平洋—印度洋实实在在存在的一种海温异常模态。对应PIOAM的正、负位相,热带印度洋和西太平洋地区的夏季(JJA)850 hPa距平风场有近乎相反的异常流场形势;对流层低层的Walker环流支和亚洲夏季风都出现了不同特征的(近乎相反)异常;在PIOAM正(负)位相将使得100 hPa的南亚高压位置偏东(西)。对热带太平洋和印度洋温跃层曲面上的海温异常(为了方便将其称为SOTA)进行EOF分解,发现其第一模态也是一个三极子模态,即当赤道中西印度洋大部分海域与赤道中东太平洋大部分海域偏暖(偏冷)时,赤道东印度洋和赤道西太平洋大部分海域则偏冷(偏暖);它与太平洋—印度洋表层的PIOAM十分类似,也表明PIOAM在海洋次表层也是存在的。高分辨海洋环流模式LICOM2.0的模拟结果,无论是对太平洋—印度洋表层还是次表层的PIOAM的特征和演变都刻画得很好,这从另一个角度进一步说明PIOAM是热带太平洋—印度洋实际存在的一种海温变化模态。PIOAM正、负位相不仅对亚洲及西太平洋地区的天气气候有非常不一样的影响(不少地方有反向的特征),还会对南北美洲和非洲一些地区产生不同影响;而且其影响与单独的厄尔尼诺(El Ni?o)及印度洋偶极子(IOD)都不尽相同。     

太阳活动11年周期对ENSO事件海温异常演变和东亚降水的影响

本文利用美国NCEP/NCAR再分析资料、海温、降水和反映太阳活动强弱的太阳10.7 cm射电流量资料,研究了1952～2010年太阳活动11年周期对ENSO年海温异常演变以及与之相联系的东亚降水的影响,在此基础上着重分析了ENSO发展期秋季东亚地区降水异常对太阳射电流量高(HS)/低(LS)的不同响应以及相关的物理过...     

孟加拉湾西南季风与南海热带季风季节内振荡特征的比较

采用美国国家环境预报中心的向外长波辐射和风场资料及日本气象厅的降水资料,用30-60d滤波后的夏季风指数在孟加拉湾和南海的区域平均值分别代表孟加拉湾西南季风和南海热带季风季节内振荡,对两支季风的季节内振荡特征进行比较分析,发现孟加拉湾西南季风的季节内振荡和南海热带季风的季节内振荡在夏季风期间(5-10月)都有约3次半的波动.夏季风期间,在阿拉伯海-西太平洋纬带上,夏季风的季节内振荡有4次从阿拉伯海的东传和3次从西太平洋的西传,其中7月后东传可直达西太平洋.孟加拉湾和南海在夏季风期间都有4次季节内振荡的经向传播,但孟加拉湾在约15°N以南为季节内振荡从热带东印度洋的北传,在约15°N以北则为副热带季风季节内振荡的南传;而在南海则是4次季节内振荡从热带的北传.在以孟加拉湾西南季风季节内振荡和南海热带季风季节内振荡分别划分的6个位相中,都存在1-3位相和4-6位相中低频对流、环流形势相反的特征,这是由热带东印度洋季节内振荡的东传和北传所致.热带印度洋季节内振荡沿西南-东北向经过约14d传到孟加拉湾,激发了孟加拉湾西南季风季节内振荡的东传,经过约6d到达南海,激发了南海热带季风季节内振荡的北传,经过约25d到达华南,形成热带印度洋季节内振荡向华南的经纬向接力传播(45d).孟加拉湾西南季风季节内振荡所影响的降水主要是在20°N以南的热带雨带随低频对流的东移而东移;而南海热带季风季节内振荡所影响的降水除了这种热带雨带随低频对流的东移外,还有在20°N以北的东亚副热带地区存在雨带随南海低频对流的北移而北移.     

The Moisture Structure of ISO in Western North Pacific Revealed by AIRS

Using the humidity profiles from the Atmospheric Infrared Sounder (AIRS) dataset, rainfall from the Tropical Rainfall Measuring Mission (TRMM) Global Precipitation Index (GPI), and surface winds from QuickSCAT (QSCAT) as well as SST from the Advanced Microwave Scanning Radiometer for NASA's Earth Observing System (AMSR-E), we analyzed the structure of summer intraseasonal oscillation (ISO) over the western North Pacific region in 2003--2004. We find that the signal of 20--90-day oscillations in the western North Pacific originates from the equatorial Indian Ocean, and propagates eastward to Philippine Sea and then moves northwestward to South China. The AIRS humidity data reveal that the boundary-layer moisture leads the mid-troposphere moisture during the ISO propagation. The positive SST anomaly may play an important role to moistening the boundary-layer, which preconditions the ISO propagation.Therefore, the intraseasonal SST anomaly could positively feed back to the atmosphere through moistening the boundary-layer,destabilizing the troposphere, and contributing to the northwestward propagation of the ISO in western North Pacific. On the other hand, the salient feature that the boundary-layer moisture anomaly leads mid-troposphere moisture does not exist in ECMWF/TOGA analysis.     

1998和1999年西北太平洋热带气旋的异常特征及其大尺度条件

应用联合台风警报中心 (JTWC)的资料 ,研究了 1998和 1999年西北太平洋 (WNP)热带气旋 (TC)的活动 ,发现这两年具有较为相似的异常特征 :台风个数明显偏少 ,台风的生成源地显著偏西。对导致这种异常的大尺度条件场的分析表明 ,1998和 1999年的台风季季风槽、垂直风切变、海平面气压等因子的分布都不利于台风在WNP东部海域的生成 ,因此是导致这两年台风偏少和生成源地异常偏西的重要原因。其中 ,季风槽的异常偏西及在盛夏的异常偏北对TC的异常活动产生了主要影响。对低纬大气环流异常的进一步分析表明 ,WNP地区的环流异常是导致季风槽和垂直风切变场异常的主要原因 ,而 1999年异常环流的出现可能是由于低纬大气对印尼附近异常热源强迫的响应所致。由于该热源的存在 ,在其东侧 (WNP地区 )激发出东传的Kelvin波 ,而相应的异常风场则表现为低层盛行异常东风 ,而高层盛行异常西风 ,因此造成了WNP东部和西部海域垂直切变场的近乎相反的变化。同时 ,由于低层异常强的东风不利于季风西风的向东延伸 ,从而使季风槽明显偏西 ,未到达菲律宾以东的热带气旋频发区的位置。     

赤道印度洋海温偶极子型振荡及其气候影响

对近百年观测资料的分析表明赤道印度洋海温(SST)确实存在着偶极子型振荡的变化特征,它在9～11月最强,而在1～4月最弱;年际变化(4～5年周期)和年代际变化(主要为20～25年周期)也十分清楚.这个偶极子主要有正位相型(海温西高东低)和负位相型(海温东高西低);一般正位相型的振幅强于负位相型.尽管在极个别年赤道印度洋海温偶极子似乎与太平洋ENSO无关,但总体而论,赤道印度洋海温偶极子与赤道太平洋海温偶极子(类似ENSO)有很好负相关.它们的联系主要是赤道大气纬向(Walker)环流.资料分析表明,赤道印度洋海温偶极子与亚洲南部流场、青藏高压和西太平洋副高都有明显关系,表明它对亚洲季风活动有重要影响.     

Modulation of Madden-Julian Oscillation Activity by the Tropical Pacific-Indian Ocean Associated Mode

In this study, the impacts of the tropical Pacific–Indian Ocean associated mode (PIOAM) on Madden–Julian Oscillation (MJO) activity were investigated using reanalysis data. In the positive (negative) phase of the PIOAM, the amplitudes of MJO zonal wind and outgoing longwave radiation are significantly weakened (enhanced) over the Indian Ocean, while they are enhanced (weakened) over the central and eastern Pacific. The eastward propagation of the MJO can extend to the central Pacific in the positive phase of the PIOAM, whereas it is mainly confined to west of 160°E in the negative phase. The PIOAM impacts MJO activity by modifying the atmospheric circulation and moisture budget. Anomalous ascending (descending) motion and positive (negative) moisture anomalies occur over the western Indian Ocean and central-eastern Pacific (Maritime Continent and western Pacific) during the positive phase of the PIOAM. The anomalous circulation is almost the opposite in the negative phases of the PIOAM. This anomalous circulation and moisture can modulate the activity of the MJO. The stronger moistening over the Indian Ocean induced by zonal and vertical moisture advection leads to the stronger MJO activity over the Indian Ocean in the negative phase of the PIOAM. During the positive phase of the PIOAM, the MJO propagates farther east over the central Pacific owing to the stronger moistening there, which is mainly attributable to the meridional and vertical moisture advection, especially low-frequency background state moisture advection by the MJO’s meridional and vertical velocities.     

热带印度洋MJO活动异常对四川盆地降水的影响

利用四川省132个气象观测站降水资料和NOAA的逐日向外长波辐射(OLR)资料,分析了主汛期热带东印度洋MJO活动异常年低频对流传播的显著差异,及其影响四川盆地主汛期降水的物理过程。探讨了热带东印度洋MJO活跃年低频振荡向四川盆地传播的路径和源头,以及孟加拉湾西南季风系统、东亚副热带季风系统的低频振荡分别对四川盆地主汛期低频对流活动的影响。结果表明:热带印度洋的低频对流激发了孟加拉湾西南季风ISO进入活跃期,并在西南气流的引导下继续向四川盆地传播;低频对流先从热带印度洋东传至菲律宾群岛南部的热带洋面,并向东亚副热带地区北传,激发了东亚副热带季风ISO的活跃加强,进而向四川盆地西传。热带印度洋MJO活动异常对四川盆地降水的调制,正是通过两支季风系统(孟加拉湾夏季风和东亚副热带夏季风)的共同作用,影响了四川盆地主汛期异常的对流活动以及降水的多寡。      

2014年8月西北太平洋和南海无TC生成之原因分析

利用常规气象观测资料、NCEP/NCAR 1°×1°的月平均再分析资料、NOAA卫星观测的OLR资料和中国气象局台风年鉴资料,对2014年8月西北太平洋和南海无TC生成的原因进行了诊断分析,结果表明：极地冷空气南侵,造成8月上中旬副热带高压偏东偏南,下旬冷空气减弱,副热带高压偏西偏南,致使副热带高压南侧偏东信风与赤道西风的汇合区位置异常偏南;马斯克林高压偏弱,导致索马里急流和东印度洋越赤道气流也弱,印度半岛中低层季风低压或季风槽极其不活跃。澳大利亚高压路径偏东或偏西和势力偏弱,则南海南部越赤道气流亦弱。8月上中旬台风主要源地的海表温度明显偏低,不能酿成低层高温高湿的大气;月内西北太平洋和南海大气的对流活动很弱,层结较稳定、风速垂直切变大,均不利于TC发生发展。在南海到菲律宾以东洋面低层为弱的正涡度区和负散度区,有辐合上升运动,但垂直速度很小,不能满足TC尺度的环流发生和发展;南亚高压和副高南侧东风扰动造成对流层高层为弱上升区,不能形成高空辐散机制,不利于上升气流维持和加强。故此,8月在异常偏南的ITCZ中生成的4个热带扰动最终均未能发展成台风。     

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 ISO Events in the Winter of 2007

The intraseasonal oscillation (ISO) events that occurred from November 2007 to February 2008 in the tropical Indian Ocean region were investigated by analyzing observational oceanic and atmospheric datasets.The results reveal that two ISO events were generated and developed from November 2007 to February 2008 in the tropical area of the Indian Ocean,which both originated from the southern African continent and propagated along a northeastward direction and finally penetrated into the equatorial eastern Indian Ocean.Compared with the general winter MJO event,which tended to travel along the equator from the western Indian Ocean into the western Pacific,the ISO of winter 2007 propagated not only along the equator into the eastern part of the Indian Ocean but was also transported northward into the subtropical region in the eastern Indian Ocean,which is more similar to the behavior of traditional summer ISO events.