夏季105～125°E垂直经圈环流变化特征及其与海温的联系

采用NCEP/NCAR再分析资料,利用质量流函数方案和EOF（empirical orthogonal function,经验正交函数）分解,研究了1979—2006年夏季105～125°E范围垂直经圈环流的变化特征及其与邻近海域海温变化的联系。结果表明：1）在105～125°E区域,夏季北半球Hadley环流明显偏强,和南半球Hadley环流对称出现,形成明显的＂Hadley环流对＂。2）小波分析显示,Hadley环流变化有准2～4a和4～6a周期。近28a来,南半球Hadley环流有南退趋势,北半球Hadley环流逐渐增强,尤其是20世纪90年代中期之前,这种变化较显著。3）105～125°E区域夏季＂Hadley环流对＂的异常和邻近海域海表温度关系密切。无论是IOD（Indian Ocean Dipole）事件还是ENSO均对东亚经圈剖面内＂Hadley环流对＂产生影响,Hadley环流的主要模态EOF1与同期和滞后的SSTA的相关在太平洋上表现出El Nino发展期、盛期的海温分布形态。南半球Hadley环流偏北（南）,北半球Hadley环流减弱（增强）,则到来的冬季的El Nino（La Nina）发展,这对ENSO事件具有一定的预报意义。IOD事件对南半球Hadley环流的影响是显著的,当负IOD事件时,南半球Hadley环流减弱,但正IOD事件时并未显著相反。     

欧亚土壤湿度异常对北半球大气环流的显著影响

用44 a ERA40再分析资料的土壤湿度和大气环流变量场, 研究持续性的欧亚大陆土壤湿度异常对后期北半球大尺度大气环流的反馈作用。首先,运用经验正交函数分解去除ENSO遥相关及趋势影响后,分析了欧亚大陆中高纬度土壤湿度变率主要模态的季节变化特征,及相对应主分量时间序列显示的土壤湿度异常的衰减时间,结果表明土壤湿度异常的主要模态在全年都表现出很好的连续性。其次,对不同季节的连续3个月的月平均土壤湿度和500 hPa高度场进行滞后最大协方差分析,研究欧亚地区中高纬度土壤湿度异常与北半球大气环流异常之间的线性耦合。第一最大协方差模态的结果表明:全年的主导信号是大气强迫土壤湿度的变化,但在冬季和夏季,大气中类似于负位相北极涛动的环流型与之前月份(最长达4个月)土壤湿度的持续变化显著相关。最后,基于土壤湿度变率中心的回归分析也证实了秋季和春季欧亚土壤湿度,特别是北非副热带,欧亚内陆和西伯利亚地区的土壤湿度异常,分别与其后的冬季和夏季的大气环流显著相关。欧亚大陆土壤湿度异常超前大气环流的信号,将有助于改善冬季和夏季北半球季节气候预报能力。     

基于交叉小波分析方法的西太平洋副热带高压年际变率与热带海温及大气环流异常的相关性研究

西太平洋副热带高压的年际变率受热带多个关键海区的海-气相互作用过程调控, 但彼此间的因果关联和影响机制尚不清楚。为揭示西太平洋副热带高压的年际变率与热带海温及大气环流异常之间的内在关联特性, 定义了三个关键海区以及赤道纬向西风区的特征指数, 并分别与西太平洋副热带高压强度、脊线指数进行了交叉小波和相干小波分析。研究发现:西太平洋副热带高压指数存在显著的2~3年和准5年的周期振荡, 20世纪八九十年代后, 由于暖池区海温及赤道纬向西风区的Hadley环流强迫加强, 致使副热带高压特征指数的2~3年周期振荡加强; 从位相关系看, 先是西太平洋副热带高压减弱南撤导致纬向西风加强, 其后影响赤道东太平洋海温升高, 同时暖水向东传, 使赤道中太平洋以及暖池区海温逐渐升高, 在Hadley环流作用下使副高加强北抬。基于上述西太平洋副热带高压的年际变率与热带海温及大气环流异常变化相关性诊断研究, 进一步探讨了造成这种相关性的影响机理和因果关联, 为揭示西太平洋副热带高压年际变率与热带海温及大气环流异常的相关性做探索研究。      

热带太平洋、印度洋海温异常对处于厄尔尼诺事件成熟期的东亚Hadley环流的影响

分析了热带太平洋El Nino事件和热带印度洋海盆一致的暖海温异常事件（记为暖海盆模态）与东亚Hadley环流的关系及海温异常对东亚Hadley环流的影响。结果表明：（1）东亚Hadley环流与El Nino循环的关系密切,El Nino事件从开始到消亡的不同位相期,东亚地区表现为随位相变化的异常经向垂直环流,在El Nino成熟期由异常顺时针经向环流圈转换为异常逆时针经向环流圈,意味着东亚Hadley环流圈的显著减弱。（2）冬季Nino3指数、赤道印度洋海盆一致型模态指数（IOBMI）与东亚Hadley环流指数间呈负相关关系,相关系数分别为-0.42、-0.39,远超过0.01信度的显著性检验,表明当El Nino事件和印度洋暖海盆模事件发生时,东亚Hadley环流减弱。模拟结果与诊断分析结果一致。（3）鉴于印度洋海盆模态和太平洋El Nino事件的密切联系,在考虑冬季东亚Hadley环流变化时,应考虑El Nino事件和印度洋海盆一致型海温异常事件的共同作用。数值试验结果表明两大洋的共同作用会产生更强的东亚异常逆时针经向垂直环流,使得东亚Hadley环流显著减弱。     

北极涛动的年代际变化及其气候影响

北极涛动(Arctic Oscillation,AO)是北半球热带外地区大气环流变率的主导模态,对北半球以及区域尺度气温变化具有重要影响.AO可在没有外强迫条件下通过d波流相互作用形成,因此它被认为是全球气候系统内部变率的重要组成部分.研究年代际尺度上AO的变化及其气候影响,可加深对当前北半球气候变化规律的物理理解,也...     

东亚和太平洋地区上空的平均垂直环流----(二)冬季

本文继《东亚和太平洋地区上空的平均垂直环流(一)夏季》之后,分析了该地区冬季平均垂直环流的特点,得出以下主要结果: 冬季南亚季风区的经向环流为强大的Hadley环流所控制,这一环流在青藏高原南侧发展得最为强盛,出了高原向东其强度逐渐减弱;在中、东太平洋的中纬度逆环流成为主要环流系统,Hadley环流远弱于夏季,只存在于赤道低纬度的低空。 本文对该地区的纬向垂直环流也进行了讨论。     

气候系统模式对Hadley环流的模拟和未来变化预估

针对全球变暖背景下未来Hadley环流将如何变化这一问题,评估了气候系统模式对1970~1999年Hadley环流时空特征的模拟效能,并在此基础上选取能合理模拟Hadley环流空间结构、强度指数和边界指数变化的3个模式,通过多模式集合方法预估了未来Hadley环流在A1B排放情景下的可能演变。预估结果表明,在全球变暖背景下,相比于1970~1999年,到本世纪末期(2070~2099年),北半球Hadley环流在4个季节都将减弱,春季变化幅度相对较弱;南半球Hadley环流在冬季和夏季也会减弱,而在春季和秋季的变化不明显。另外,北半球Hadley环流的北边界除在夏季向南收缩外,在其它3个季节均向北伸展;南半球Hadley环流的南边界在4个季节均向极地方向移动。两个半球的Hadley环流在垂直方向还将向对流层上层伸展。       

1948-2004年全球平均Hadley环流强度指数与特征

利用NCEP/NCAR逐月平均风场资料,研究了全球平均Hadley环流特征.利用3层4个关键区的风定义并计算了1948年1月-2004年12月的全球纬向平均的南/北半球和全球Hadley环流逐月强度指数.结果表明:计算的Hadley环流指数可以合理地表示Hadley环流的强度;北半球Hadley环流除7-9月(南半球除5月)外都呈增强趋势;南/北半球的年平均Hadley环流也是增强的.年际相关分析表明:Hadley环流指数与SOI有非常高的负相关,Hadley环流强度的年际变化与ENSO关系密切.     

春季Hadley环流强度与我国东部地区夏季降水的联系

该文利用1983--2012年ERA—INTERIM风场的月平均资料以及中国160站月降水资料（1983-2012年）,研究Hadley环流的季节和年际变化特征,我国东部地区夏季降水分布及北半球春季Hadley环流强度与我国东部地区夏季降水的关系。结果表明：Hadley环流存在明显的季节变化特征,北半球环流强度在冬季最强,夏季时最弱,并且环流强度越强时,范围就越大;Hadley环流强度各季节年际变化较明显,而年代际变化秋季较明显。春季HMley环流强度与我国华南地区、长江流域地区和华北地区夏季降水呈“负正负”的相关关系。利用合成分析的得到的结果与其相一致。     

热带太平洋低层环流主模态与东亚大气环流的可能联系

利用1958—2001年NCEP/NCAR再分析资料,探讨了热带太平洋(100°E~60°W,10°S~10°N)10 m风场的时空变化特征及其与东亚大气环流的可能联系。结果表明:1)热带太平洋风场异常存在两种主模态,第一模态对应中西太平洋一致的西(东)风异常,关于赤道呈准对称分布,与ENSO(El Nio-Southern Oscillation)暖(冷)位相时风场的分布对应;第二模态则关于赤道呈反对称分布,西北太平洋存在显著的反气旋(气旋)式环流,中太平洋异常西风不再位于赤道上,而是南移到了10°S左右,对应ENSO暖(冷)位相向相反位相转换时的风场分布特征。2)两模态时间系数的主振荡周期不同,与ENSO循环的位相关系也不同。研究发现,当两模态呈正(负)位相分布时,贝加尔湖南侧(South to Lake Baikal,SLB)容易发生持续的高压(低压)异常环流。3)两模态与SLB异常环流的联系途径不同。第一模态正位相对应热带中东太平洋大范围暖海温引起的二极型Walker环流异常,SLB异常高压不仅能通过东亚沿岸北风和南海低槽的作用促进第一模态的前期发展,还对其后期维持起重要作用。负位相时,情况相反。该环流系统既与热带中东太平洋大范围垂直运动有关,还与邻近的中国东南沿海低层异常辐合有关;第二模态则对应热带西太平洋及东印度洋为主、大西洋为辅的暖海温引起的热带四极型Walker环流异常。此时热带西太平洋到东印度洋局地偏强的经圈Hadley环流可能是SLB异常环流维持的主要原因。     

Asymmetric Variations in the Tropical Ascending Branches of Hadley Circulations and the Associated Mechanisms and Effects

This study investigates the variations in the tropical ascending branches(TABs) of Hadley circulations(HCs) during past decades, using a variety of reanalysis datasets. The northern tropical ascending branch(NTAB) and the southern tropical ascending branch(STAB), which are defined as the ascending branches of the Northern Hemisphere HC and Southern Hemisphere HC, respectively, are identified and analyzed regarding their trends and variability. The reanalysis datasets consistently show a persistent increase in STAB during past decades, whereas they show less consistency in NTAB regarding its decadalto multidecadal variability, which generally features a decreasing trend. These asymmetric trends in STAB and NTAB are attributed to asymmetric trends in the tropical SSTs. The relationship between STAB/NTAB and tropical SSTs is further examined regarding their interannual and decadal-to multidecadal variability. On the interannual time scale, the STAB and NTAB are essentially modulated by the eastern-Pacific type of ENSO, with a strengthened(weakened) STAB(NTAB) under an El Ni ?no condition. On the decadal-to multidecadal time scale, the variability of STAB and NTAB is closely related to the southern tropical SSTs and the meridional asymmetry of global tropical SSTs, respectively. The tropical eastern Pacific SSTs(southern tropical SSTs) dominate the tropical SST–NTAB/STAB relationship on the interannual(decadal-to multidecadal)scale, whereas the NTAB is a passive factor in this relationship. Moreover, a cross-hemispheric relationship between the NTAB/STAB and the HC upper-level meridional winds is revealed.     

观测分析非洲南部地区土壤湿度异常对南半球大气环流的显著影响

本文基于44年ERA40再分析月平均土壤湿度资料和大气环流变量场资料,去除ENSO遥相关以及趋势影响后,利用滞后最大协方差方法分析非洲南部地区土壤湿度分布与南半球大气环流异常之间的线性耦合。第一最大协方差模态的结果表明:在南半球冬季（Jun-Jul-Aug,6～8月）和夏季（Jan-Feb-Mar,1～3月）,大气中类似南极涛动（Antarctic Oscillation,简称AAO）正位相的环流型与超前月份（最长时间达到5个月）的非洲南部地区土壤湿度的异常分布显著相关。基于土壤湿度变率中心的线性回归分析方法证实非洲南部地区其北部土壤湿度正异常、中南部土壤湿度负异常的空间分布对后期夏季和冬季的大气有显著的反馈作用。诊断结果显示由于夏秋季节和春季初夏非洲南部地区土壤湿度异常均有显著的持续性,同时对后期AAO产生持续增强作用,所以滞后最大协方差方法可以检测出它们对后期AAO的显著影响。以上非洲南部地区土壤湿度异常超前于南极涛动的信号,将有助于加强对土壤湿度反馈机制及其对南半球大尺度环流变率影响的认识。     

Simulation of the equatorially asymmetric mode of the Hadley circulation in CMIP5 models

The tropical Hadley circulation (HC) plays an important role in influencing the climate in the tropics and extra-tropics. The realism of the climatological characteristics, spatial structure, and temporal evolution of the long-term variation of the principal mode of the annual mean HC (i.e., the equatorially asymmetric mode, EAM) was examined in model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The results showed that all the models are moderately successful in capturing the HC's climatological features, including the spatial pattern, meridional extent, and intensity, but not the spatial or temporal variation of the EAM. The possible reasons for the poor simulation of the long-term variability of the EAM were explored. None of the models can successfully capture the differences in the warming rate between the tropical Southern Hemisphere (SH) and Northern Hemisphere (NH), which is considered to be an important driver for the variation of the AM. Most of the models produce a faster warming in the NH than in the SH, which is the reverse of the observed trend. This leads to a reversed trend in the meridional gradient between the SH and NH, and contributes to the poor simulation of EAM variability. Thus, this aspect of the models should be improved to provide better simulations of the variability of the HC. This study suggests a possible reason for the poor simulation of the HC, which may be helpful for improving the skill of the CMIP5 models in the future.     

Variability patterns of Rossby wave source

Rossby waves (RW) propagation due to a local forcing is one of the mechanisms responsible for wave trains configurations known as teleconnections. The term teleconnection refers to anomalies patterns that are correlated in several regions of the world, causing large-scale changes in atmospheric waves patterns and temperature and precipitation regimes. The aim of teleconnections studies is to provide a better understanding of atmospheric variability and their mechanisms of action in order to identify patterns that can be tracked and predicted. The purpose of this study was to characterize seasonal and spatial variability of atmospheric RW sources. The RW source at 200?hPa was calculated for the four seasons with reanalysis data of zonal and meridional wind. In the Northern Hemisphere (NH), the RW sources were located on East Asia, North America, North Atlantic and Pacific. The main RW sources in the Southern Hemisphere (SH) were located over Intertropical, South Pacific, South Atlantic and South Indian Convergence Zones. Extratropical regions were also identified, mainly to the south of Australia. The vortex stretching term (S1) and the advection of absolute vorticity by the divergent wind (S2) were analyzed to discuss the physical mechanisms for RW generation. In the NH, the source at East Asia in DJF changed to a sink in JJA, related to the dominance of S1 term in DJF and S2 term in JJA. In the SH, the vortex stretching term had the dominant contribution for RW source located to the south of Australia. The main forcing for RW sources at east of Australia was the advection of absolute vorticity by divergent flow. Over South America, both terms contributed to the source in DJF. The main modes of RW source variability were discussed by using empirical orthogonal functions analysis. RW variability was characterized by wave trains configurations in both hemispheres over regions of jet streams and storm tracks, associated with favorable and unfavorable areas for RW generation.     

东北冷涡持续活动时期的北半球500 hPa环流特征分析

分别对5月和6～8月东亚东北冷涡活动典型的多寡年份北半球500 hPa高度距平场进行合成、频次累积和相关分析,结果表明:东亚东北冷涡持续性活动不仅与前期、同期和后期北半球的大气环流异常密切相关,而且也是异常区的重要组成部分;500hPa 5月和6～8月东北冷涡活动多寡年的同期500hPa高度距平合成场差异显著;6～8月东北冷涡典型多寡年的同期距平场均与前冬(12～2月)的主要异常区反位相,存在半年尺度的遥相关,与北太平洋涛动(NPO)类同的500 hPa高度距平场,如前冬呈正位相,预报6～8月东北冷涡持续活动弱,反之,冷涡持续活动强;合成场和相关场通过信度检验的关键区主要位于东亚中高纬度至阿留申群岛及其以南的副热带地区、青藏高原接近巴基斯坦一侧和北非乍得盆地与撒哈拉大沙漠等地区;由此可以认为东亚地区中高纬度5月和6～8月东北冷涡持续性活动是北半球大气环流异常持续或调整的重要表征.     

A brief introduction to the issue of climate and marine fisheries

Climatic variability has profound effects on the distribution, abundance and catch of oceanic fish species around the world. The major modes of this climate variability include the El Niño-Southern Oscillation (ENSO) events, the Pacific Decadal Oscillation (PDO) also referred to as the Interdecadal Pacific Oscillation (IPO), the Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM) and the North Atlantic Oscillation (NAO). Other modes of climate variability include the North Pacific Gyre Oscillation (NPGO), the Atlantic Multidecadal Oscillation (AMO) and the Arctic Oscillation (AO). ENSO events are the principle source of interannual global climate variability, centred in the ocean–atmosphere circulations of the tropical Pacific Ocean and operating on seasonal to interannual time scales. ENSO and the strength of its climate teleconnections are modulated on decadal timescales by the IPO. The time scale of the IOD is seasonal to interannual. The SAM in the mid to high latitudes of the Southern Hemisphere operates in the range of 50–60 days. A prominent teleconnection pattern throughout the year in the Northern Hemisphere is the North Atlantic Oscillation (NAO) which modulates the strength of the westerlies across the North Atlantic in winter, has an impact on the catches of marine fisheries. ENSO events affect the distribution of tuna species in the equatorial Pacific, especially skipjack tuna as well as the abundance and distribution of fish along the western coasts of the Americas. The IOD modulates the distribution of tuna populations and catches in the Indian Ocean, whilst the NAO affects cod stocks heavily exploited in the Atlantic Ocean. The SAM, and its effects on sea surface temperatures influence krill biomass and fisheries catches in the Southern Ocean. The response of oceanic fish stocks to these sources of climatic variability can be used as a guide to the likely effects of climate change on these valuable resources.     

1948～2001年全球陆地及大尺度区域6～8月旱涝气候变化

用 1 948～ 2 0 0 1全球陆地月降水资料 (PREC/L) ,研究了全球、北半球、南半球及欧亚、非洲、澳洲、北美、南美和南极大陆等 6个大尺度区域 6～ 8月的旱涝气候变化。结果表明 ,全球及北、南半球 6～ 8月的旱涝有明显的年代际变化。 2 0世纪 40年代末～ 70年代为全球洪涝多发期 ,80～ 90年代为全球干旱多发期。北半球的特征与全球较为一致 ;南、北半球 6～ 8月的旱涝没有明显的联系 ,但发生暖 (冷 )事件时 ,两个半球可能同时出现干旱(洪涝 ) ;全球、半球的旱涝与ENSO有明显的联系。另外 ,非洲大陆和欧亚大陆旱涝年的分布有十分明显的年代际特征 ,6个大区域 6～ 8月的旱涝之间存在一定的联系。     

Predictability of Northwest Pacific climate during summer and the role of the tropical Indian Ocean

A seasonal forecast system based on a global, fully coupled ocean?Catmosphere general circulation model is used to (1) evaluate the interannual predictability of the Northwest Pacific climate during June?CAugust following El Ni?o [JJA(1)], and (2) examine the contribution from the tropical Indian Ocean (TIO) variability. The model retrospective forecast for 1983?C2006 captures major modes of atmospheric variability over the Northwest Pacific during JJA(1), including a rise in sea level pressure (SLP), an anomalous anticyclone at the surface, and a reduction in subtropical rainfall, and increased rainfall to the northeast over East Asia. The anomaly correlation coefficient (ACC) for the leading principal components (PCs) of SLP and rainfall stays above 0.5 for lead time up to 3?C4?months. The predictability for zonal wind is slightly better. An additional experiment is performed by prescribing the SST climatology over the TIO. In this run, designated as NoTIO, the Northwest Pacific anticyclone during JJA(1) weakens considerably and reduces its westward extension. Without an interactive TIO, the ACC for PC prediction drops significantly. To diagnose the TIO effect on the circulation, the differences between the two runs (Control minus NoTIO) are analyzed. The diagnosis shows that El Nino causes the TIO SST to rise and to remain high until JJA(1). In response to the higher than usual SST, precipitation increases over the TIO and excites a warm atmospheric Kelvin wave, which propagates into the western Pacific along the equator. The decrease in equatorial SLP drives northeasterly wind anomalies, induces surface wind divergence, and suppresses convection over the subtropical Northwest Pacific. An anomalous anticyclone forms in the Northwest Pacific, and the intensified moisture transport on its northwest flank causes rainfall to increase over East Asia. In the NoTIO experiment, the Northwest Pacific anticyclone weakens but does not disappear. Other mechanisms for maintaining this anomalous circulation are discussed.     

Interdecadal change in the connection between Hadley circulation and winter temperature in East Asia

Based on NCEP/NCAR reanalysis data, the interdecadal variability of Hadley circulation （HC） and its association with East Asian temperature in winter are investigated. Results indicate that the Northern Hemisphere winter HC underwent apparent change in the 1970s, with transition occurring around 1976/77. Along with interdecadal variability of HC, its linkage to surface air temperature （SAT） in East Asia also varied decadally, from weak relations to strong relations. Such a change may be related to the interaction between HC and the atmospheric circulation system over the Philippines, which is associated with the East Asian winter monsoon （EAWM）. Before the 1970s, the connection between HC and the anticyclonic circulation around the Philippines was insignificant, but after the late 1970s their linkage entered a strong regime. The intensification of this connection may therefore be responsible for the strong relations between HC and East Asian winter temperatures after the late 1970s.     

How predictable is the northern hemisphere summer upper-tropospheric circulation?

The retrospective forecast skill of three coupled climate models (NCEP CFS, GFDL CM2.1, and CAWCR POAMA 1.5) and their multi-model ensemble (MME) is evaluated, focusing on the Northern Hemisphere (NH) summer upper-tropospheric circulation along with surface temperature and precipitation for the 25-year period of 1981–2005. The seasonal prediction skill for the NH 200-hPa geopotential height basically comes from the coupled models’ ability in predicting the first two empirical orthogonal function (EOF) modes of interannual variability, because the models cannot replicate the residual higher modes. The first two leading EOF modes of the summer 200-hPa circulation account for about 84% (35.4%) of the total variability over the NH tropics (extratropics) and offer a hint of realizable potential predictability. The MME is able to predict both spatial and temporal characteristics of the first EOF mode (EOF1) even at a 5-month lead (January initial condition) with a pattern correlation coefficient (PCC) skill of 0.96 and a temporal correlation coefficient (TCC) skill of 0.62. This long-lead predictability of the EOF1 comes mainly from the prolonged impacts of El Niño-Southern Oscillation (ENSO) as the EOF1 tends to occur during the summer after the mature phase of ENSO. The second EOF mode (EOF2), on the other hand, is related to the developing ENSO and also the interdecadal variability of the sea surface temperature over the North Pacific and North Atlantic Ocean. The MME also captures the EOF2 at a 5-month lead with a PCC skill of 0.87 and a TCC skill of 0.67, but these skills are mainly obtained from the zonally symmetric component of the EOF2, not the prominent wavelike structure, the so-called circumglobal teleconnection (CGT) pattern. In both observation and the 1-month lead MME prediction, the first two leading modes are accompanied by significant rainfall and surface air temperature anomalies in the continental regions of the NH extratropics. The MME’s success in predicting the EOF1 (EOF2) is likely to lead to a better prediction of JJA precipitation anomalies over East Asia and the North Pacific (central and southern Europe and western North America).