近百年全球平均气温年际变化型态的低频变率特征

利用时间上扩展的经验正交函数（TEEOF）分析方法，对近百年全球及南北半球平均气温一年、三年、六年和十年的变化形态及其频率进行诊断，结果表明，TEEOF第一模态占总方差贡献的50％以上，各种年际振动的第一模态基本上代表了与气候变化有关的年变化型，并能反映出气温的长期趋势变化，特别是十年际的第一模态，冬季气温湿示出较强的上升趋势，相应的第一时间主分量趋势与实际温度序列的走势非常一致。全球及南北半球各时域TEEOF除第一模态及一年TEEOF的第模态外，其它特同量所表示的年际变化型态各有差异，相应主分量都与一定的年际准周期振动结构的长期变率有关。年变化型态的T^2检验表明，南半球及全球的突变时间与年平均气温单要素t检验结果差异不大，而北半球的差异明显，表明T^2检验，对具有多变量的型态突变的检测比单要素的t检验理为合理。     

STUDY ON THE RELATIONSHIP BETWEEN THE DECADAL VARIATIONS OF ANNUALLY FIRST RAINY SEASON PRECIPITATION OF GUANGXI AND SEA SURFACE TEMPERATURE OF INDIAN OCEAN IN SOUTHERN HEMISPHERE

Decadal circulation differences between more and less rainfall periods in the annually first rainy season of Guangxi and their association with sea surface temperature (SST) of the austral Indian Ocean are investigated by using the NCEP/NCAR reanalysis data. The results are shown as follows. A pattern in which there is uniform change of the Guangxi precipitation shows a 20-year decadal oscillation and a 3-year interannual change. In contrast, a pattern of reversed-phase change between the north and the south of Guangxi has a 6-year interannual periodicity and quasi-biennial oscillation. In the period of more precipitation, the surface temperature in Eurasia is positively anomalous so as to lead to stronger low pressure systems on land and larger thermal contrast between land and ocean. Therefore, the air column is more unstable and ascending flows over Guangxi are intensified while the Hadley cell is weakened. Furthermore, the weaker western Pacific subtropical high and South Asia High, together with a stronger cross-equatorial flow, result in the transportation of more humidity and the appearance of more precipitation. The correlation analysis indicates that the Indian Ocean SST in Southern Hemisphere is closely associated with the variation of the seasonal precipitation of Guangxi on the decadal scale by influencing the Asian monsoon through the cross-equatorial flow.     

Physical processes responsible for the interannual variability of sea ice concentration in Arctic in boreal autumn since 1979

Arctic sea ice concentration (ASIC) in boreal autumn exhibits prominent interannual variability since 1979. The physical mechanism responsible for the year-to-year variation of ASIC is investigated through observational data analyses and idealized numerical modeling. It is found that the ASIC interannual variability is closely associated with the anomalous meridional circulations over the Northern Hemisphere, which is further linked with the tropical sea surface temperature (SST) forcing. A tropics-wide SST cooling anomaly leads to an enhanced meridional SST gradient to the north of the equator in boreal summer, generating strengthened and northward shifting Hadley circulation over the Northern Hemisphere. Consequently, the meridional circulations are enhanced and pushed poleward, leading to an enhanced descending motion at the North Pole, surrounded by an ascending motion anomaly; the surface outflow turns into easterly anomalies, opposing the mean-state winds. As a result, positive cloudiness and weakened surface wind speed emerge, which reduce ASIC through changes in the surface latent heat flux and the downward longwave radiation.     

广西前汛期降水年代际变化与南半球印度洋海温的关系

利用NCEP/NCAR月平均再分析资料对广西前汛期降水年代际变化的环流差异及其与前期南半球印度洋海温的关系进行研究,结果表明:广西前汛期整体一致变化的降水分布型具有20年左右年代际振荡及3年左右的年际周期,桂南、桂北反相变化的降水空间型具有6年和准两年振荡.在前汛期降水偏多期,欧亚大陆地表温度偏高,热力作用增强,造成大陆热低压偏强,海陆差异加大,广西区域气柱不稳定性增强,上升气流显著增强,Hadley环流减弱,西太平洋副高及南亚高压减弱,南北半球越赤道气流增强,高原南侧南支槽气流加强,水汽输送增多,造成广西降水偏多;降水偏少期形势相反.相关分析表明前期2～3月南半球中纬度印度洋海温与广西前汛期降水年代际变化呈明显负相关,意味着南半球海温对广西前汛期降水年代际变化有调控作用,这种作用是通过海温异常影响越赤道气流从而影响亚洲季风的强弱而实现的.     

1988～1998年北半球积雪时空变化特征分析

利用NOAA提供的北半球近10年(1988～1998)逐周雪盖观测资料，通过引入年或季节累积雪盖周数作为对雪量累积情况的定量衡量，对北半球雪盖变化时空特征进行了分析。结果表明:近10年来，北半球积雪年际变化的关键区位于青藏高原、蒙古高原、欧洲阿尔卑斯山脉及北美中西部，其中青藏高原是北半球积雪异常变化最强烈的区域。青藏高原和欧亚大陆其他地区积雪变化的关联表现为两种不同的时空变化型，第一种型表现为青藏高原地区和其他地区(如欧洲、俄罗斯远东地区)积雪的同位相趋势性增多；第二种型表现为青藏高原地区和中亚地区积雪变化同位相，而和蒙古高原－我国东北地区积雪变化反位相的年际振荡。     

Mean climatic characteristics in high northern latitudes in an ocean-sea ice-atmosphere coupled model

Emphasizing the model‘s ability in mean climate reproduction in high northern latitudes, resultsfrom an ocean-sea ice-atmosphere coupled model are analyzed. It is shown that the coupled model cansimulate the main characteristics of annual mean global sea surface temperature and sea level pressurewell, but the extent of ice coverage produced in the Southern Hemisphere is not large enough. The maindistribution characteristics of simulated sea level pressure and temperature at 850 hPa in high northernlatitudes agree well with their counterparts in the NCEP reanalysis dataset, and the model can reproducethe Arctic Oscillation (AO) mode successfully. The simulated seasonal variation of sea ice in the NorthernHemisphere is rational and its main distribution features in winter agree well with those from observations.But the ice concentration in the sea ice edge area close to the Eurasian continent in the inner Arctic Oceanis much larger than the observation. There are significant interannual variation signals in the simulated seaice concentration in winter in high northern latitudes and the most significant area lies in the GreenlandSea, followed by the Barents Sea. All of these features agree well with the results from observations.     

Interannual variation of the Asian-Pacific oscillation

Previous studies have identified an Asian-Pacific Oscillation (APO) teleconnection pattern, which exhibits an out-of-phase relationship in the summer tropospheric temperature with warming over the Eurasia and cooling over the Northern Pacific and the Northern America, and vice versa. But the interannual variation of this teleconnection remains obscure. This study points out that interannual variation of the APO teleconnection is associated with the second empirical orthogonal function (EOF) mode of the northern-hemisphere upper tropospheric temperature during boreal summer, which accounts for 14% of the variance. A heat budget analysis is conducted for the Eurasian region and the North Pacific region respectively to reveal the cause of the zonal dipole mode temperature structure. For the Eurasia region, the warming is contributed by the adiabatic heating process due to downward vertical motion anomalies. For the Northern Pacific region, the temperature variation is mainly contributed by zonal advection associated with interannual zonal wind perturbation acting on the climatological temperature gradient. Composite analysis and numerical experiments with an atmospheric general circulation model (AGCM) shows the interannual zonal wind perturbation is related to the sea surface temperature anomalies over the equatorial eastern Pacific.     

平流层30 hPa月平均高度场的气候特征

采用经验正交函数分解(EOF)方法对NCEP／NCAR全球再分析资料中1958—1997年共40年,30hPa月平均高度和月平均风场进行了分析,讨论了40年平流层的主要特征向量和相应时间系数的变化特征,发现高度场的EOF第一模态具有很好的空间整体性和明显的季节变化。在平流层中,北半球冬季为一较大的环极冷低压,夏季为一以整个半球为规模的环极暖高压。并以1月和7月代表冬、夏季,选取1月和7月的40年资料作为时间序列,用EOF分析了冬、夏季不同的空问振荡型的特征,运用小波分析方法考察了其年际及年代际变化周期。并据此定义了不同的振荡型指数,为以后分析平流层要素场与气候变化的关系奠定了基础。     

全球海气系统年际和年代际变化的时空特征分析

本文利用从1950－1998年共计49年的马里兰（Maryland）大学全球海洋同化分析资料和NCEP全球大气再分析资料，分析了全球海气系统年际和年代际变化的主要时空特征，结果表明：1）全球上层海洋年际变化的主要模态是位于热带太平洋的ENSO模态，海洋年代际变化的最显著区域为南半球高纬度及中纬度海洋特别是赤道以外区域的热带东太平洋和大西洋；2）全球大气年际和年代际变化都主要位于中高纬度地区尤其是两极地区，在年际时间尺度上，气温异常和气压异常没有明显的对应关系，但在年代际时间尺度上，气温增暖（变冷）常常伴随着气压的降低（升高）；3）在年际时间尺度上，发生在中高纬度陆地地区的大气年际变化和主要发生热带海洋上层海洋年际变化没有一致性的内在联系，前者主要表现为大气的内部（浑沌）变化，而后者主要为热带海气相互作用产生的ENSO变化；4）在年代际时间尺度上，全球海洋大气系统大约在70年代前后，均一致性地经历了一次跃变，其结果是导致80年代以来，全球大范围地区（尤其是两极和西伯利亚地区）气温明显偏暖，赤道两侧的热带东太平洋、北美和南美西海岸、及非洲西海岸等海域海表面温度偏高，伴随着这种全球大范围背景增暖现象，青藏高原北部和格陵兰岛区域气温具有变冷的趋势，而南半球高纬度海域海表温度也表现为降低。     

Spatio-temporal Variability of Northern Hemipheric Sea Level Pressure(SLP)and Precipitation over the Mid-to-Low Reaches of the Yangtze River

The spatio-temporal variability of Northern Hemisphere Sea Level Pressure(SLP)and precipitation over the mid-to-low reaches of the Yangtze River(PMLY)is analyzed jointly using the multi-taper/singular value decomposition method(MTM-SVD).Statistically significant narrow frequency bands are obtained from the local fractional variance(LFV)spectrum.Significant interdecadal(i.e.,16-to-18-year periods)and interannual(i.e.,3-to-6-year periods)signals are identified.Moreover,a significant quasi-biennial signal is identified but only for PMLY data.The spatial joint evolution of patterns obtained for peaks in the LFV spectrum sheds light on relationships between SLP and PMLY:the Arctic Oscillation(AO)modulates the variability of the PMLY while the interannual variability of PMLY is in phase with the Northern Atlantic Oscillation(NAO)and the Northern Pacific Oscillation(NPO).     

Spatio-temporal Variability Sea Level Pressure （SLP） the Mid-to-Low Reaches of Northern Hemipheric and Precipitation over of the Yangtze River

The spatio-temporal variability of Northern Hemisphere Sea Level Pressure （SLP） and precipitation over the mid-to-low reaches of the Yangtze River （PMLY） is analyzed jointly using the multi-taper/singular value decomposition method （MTM-SVD）. Statistically significant narrow frequency bands are obtained from the local fractional variance （LFV） spectrum. Significant interdecadal （i.e., 16-to-18-year periods） and interannual （i.e., 3-to-6-year periods） signals are identified. Moreover, a significant quasi-biennial signal is identified but only for PMLY data. The spatial joint evolution of patterns obtained for peaks in the LFV spectrum sheds light on relationships between SLP and PMLY： the Arctic Oscillation （AO） modulates the variability of the PMLY while the interannual variability of PMLY is in phase with the Northern Atlantic Oscillation （NAO） and the Northern Pacific Oscillation （NPO）.     

Stratospheric climate and variability from a general circulation model and observations

The climate and natural variability of the large-scale stratospheric circulation simulated by a newly developed general circulation model are evaluated against available global observations. The simulation consisted of a 30-year annual cycle integration performed with a comprehensive model of the troposphere and stratosphere. The observations consisted of a 15-year dataset from global operational analyses of the troposphere and stratosphere. The model evaluation concentrates on the simulation of the evolution of the extratropical stratospheric circulation in both hemispheres. The December–February climatology of the observed zonal mean winter circulation is found to be reasonably well captured by the model, although in the Northern Hemisphere upper stratosphere the simulated westerly winds are systematically stronger and a cold bias is apparent in the polar stratosphere. This Northern Hemisphere stratospheric cold bias virtually disappears during spring (March–May), consistent with a realistic simulation of the spring weakening of the mean westerly winds in the model. A considerable amount of monthly interannual variability is also found in the simulation in the Northern Hemisphere in late winter and early spring. The simulated interannual variability is predominantly caused by polar warmings of the stratosphere, in agreement with observations. The breakdown of the Northern Hemisphere stratospheric polar vortex appears therefore to occur in a realistic way in the model. However, in early winter the model severely underestimates the interannual variability, especially in the upper troposphere. The Southern Hemisphere winter (June–August) zonal mean temperature is systematically colder in the model, and the simulated winds are somewhat too strong in the upper stratosphere. Contrary to the results for the Northern Hemisphere spring, this model cold bias worsens during the Southern Hemisphere spring (September–November). Significant discrepancies between the model results and the observations are therefore found during the breakdown of the Southern Hemisphere polar vortex. For instance, the simulated Southern Hemisphere stratosphere westerly jet continuously decreases in intensity more or less in situ from June to November, while the observed stratospheric jet moves downward and poleward.This paper was presented at the Third International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 4–8 Sept. 1995 under the auspice of the Max Planck Institute for Meteorology, Hamburg. Editor for these papers is L. Dümenil.     

Evaluation of Surface Air Temperature Change over China and the Globe during the Twentieth Century in IAP AGCM4.0

Based on time series and linear trend analysis, the authors evaluated the performance of the fourth generation atmospheric general circulation model developed at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP AGCM4.0), in simulating surface air temperature (SAT) during the twentieth century over China and the globe. The numerical experiment is conducted by driving the model with the observed sea surface temperature and sea ice. It is shown that IAP AGCM4.0 can simulate the warming trend of the global SAT, with the major warming regions in the high latitudes of the Northern Hemisphere and the mid-latitudes of the Southern Hemisphere. While the simulated trend over the whole globe is close to the observation, the model under-estimates the observed trend over the continents. More-over, the model simulates the spatial distribution of SAT in China, with a bias of approximately-2°C in eastern China, but with a more serious bias in western China. Compared with the global mean, however, the correlation coefficient between the simulation and observation in China is significantly lower, indicating that there is large uncertainty in simulating regional climate change.     

20世纪70年代末前后北半球冬季对流层遥相关的时空演变研究

应用NOAA提供的1950～2008年月平均500 hPa高度场再分析资料、海表温度、太平洋年代际振荡(PDO)指数和大西洋三极模(ATM)指数, 研究了20世纪70年代末前后北半球冬季对流层遥相关的时空演变规律。相关分析、Mann-Kendall分析和凝聚小波分析的结果表明, 20世纪70年代末以来, 太平洋—北美(PNA)型、欧亚(EUP)型、西太平洋(WP)型和西大西洋(WA)型四种遥相关空间分布和时间演变产生较为显著的变化。空间分布的变化既体现在遥相关正、负异常中心的强度上, 也体现在正、负异常的范围上; 时间演变方面的变化则体现在PNA和WP遥相关指数具有上升趋势, EUP和WA遥相关指数具有一定下降趋势。20世纪70年代末以来, 影响北半球冬季5种遥相关型的海温关键区均有所改变。其中, 各大洋上影响EUP遥相关型的海温关键区面积显著缩小, 影响WA遥相关型的太平洋海温关键区面积显著缩小, 影响EA遥相关型海温关键区在北大西洋中南部改变明显; 在16年以上时间尺度上, PDO变化是造成北半球冬季PNA、 EUP、 WP三种遥相关型变化的主要原因; ATM变化是造成北半球冬季WA和EA两种遥相关型变化的主要原因。     

热带太平洋SST异常对IAP-9 LAGCM 年际变率影响的模拟

通过1960~1989年实测的热带太平洋(30.5°N~30.5°S,120°E~70°W)SST(热带太平洋区域以外用气候平均值)强迫AGCM得到的结果,以此来研究热带SST的变化对全球大气环流年际变化的影响。首先,我们分析了南方涛动,分别给出了Tahiti和Darwin海平面气压异常及赤道附近(-5°S~5°N)外逸长波辐射(OLR)时间演变,都能很好与观测相比较。然后,讨论了全球大气环流对热带SST的变化的响应,全球主要的遥相关型都能很好地再现。最后,通过奇异值分解(SVD)技术研究了热带SST与冬季北半球500 hPa位势高度主要的耦合型,模拟的相关型与NCEP再分析资料的相关型非常相似。     

Variability of seasonal-mean fields arising from intraseasonal variability. Part 3: Application to SH winter and summer circulations

A study has been made, using the National Centers for Environmental Prediction and National Center for Atmospheric Research re-analysis 500 hPa geopotential height data, to determine how intraseasonal variability influences, or can generate, coherent patterns of interannual variability in the extratropical summer and winter Southern Hemisphere atmospheric circulation. In addition, by separating this intraseasonal component of interannual variability, we also consider how slowly varying external forcings and slowly varying (interannual and longer) internal dynamics might influence the interannual variability of the Southern Hemisphere circulation. This slow component of interannual variation is more likely to be potentially predictable. How sea surface temperatures are related to the slow components is also considered. The four dominant intraseasonal modes of interannual variability have horizontal structures similar to those seen in both well-known intraseasonal dynamical modes and statistical modes of intraseasonal variability. In particular, they reflect intraseasonal variability in the high latitudes associated with the Southern Annular Mode, and wavenumber 4 (summer) and wavenumber 3 (winter) patterns associated with south Pacific regions of persistent anomalies and blocking, and possibly variability related to the Madden-Julian Oscillation (MJO). The four dominant slow components of interannual variability, in both seasons, are related to high latitude variability associated with the Southern Annular Mode, El Nino Southern Oscillation (ENSO) variability, and South Pacific Wave variability associated with Indian Ocean SSTs. In both seasons, there are strong linear trends in the first slow mode of high latitude variability and these are shown to be related to similar trends in the Indian Ocean. Once these are taken into account there is no significant sea surface temperature forcing of these high latitude modes. The second and third ENSO related slow modes, in each season, have high correlations with tropical sea surface temperature variability in the Pacific and Indian Oceans, both contemporaneously and at one season lag. The fourth slow mode has a characteristic South Pacific wave structure of either a wavenumber 4 (summer) or wavenumber 3 (winter) pattern, with strongest loadings in the South Pacific sector, and an association simultaneously with a dipole SST temperature gradient in the subtropical Indian Ocean.     

Variability of seasonal-mean fields arising from intraseasonal variability. part 2, application to nh winter circulations

A method for studying patterns of interannual variability arising from intraseasonal variability has been applied to the extratropical Northern Hemisphere wintertime 500 hPa geopotential height, using data from the NCEP-NCAR. These patterns describe the effects predominantly of intraseasonal variability and blocking. Removing this component from the sample interannual covariance matrix, one can define a residual, or slow, component of interannual variability that is more closely related to external forcings and very slowly varying (interannual/supra-annual) internal dynamics. For the Northern Hemisphere NCEP-NCAR reanalysis data, there are considerable differences between the intraseasonal patterns and the total patterns. The intraseasonal patterns are more spatially localized and more closely related to known intraseasonal variability, especially blocking events and the Madden-Julian Oscillation. Although the slow patterns and the total patterns look similar, they have some important differences. The slow patterns are more closely related to the slowly varying external forcing and very low-frequency internal dynamics than those derived by the sample covariance matrix. This is evidenced by the fact that the principal component time series of the slow patterns have a larger proportion of variability related to these factors. Where tropical SST forcing is important, the slow patterns tended to be more highly correlated with the interannual variations in the forcing. Three slow modes, related to the Tropical Northern Hemisphere, East Atlantic and Western Pacific teleconnections, are all significantly related to tropical SST variability associated predominantly with the El Nino-Southern Oscillation, in the case of the first two, and Indian Ocean variability, in the third case. The derived slow patterns and intraseasonal patterns may help to better understand the long-range predictability, uncertainty, and forcing of climate variables, for the wintertime circulation.     

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,也可为预估未来年代际尺度上气候变化及其不确定性提供科学依据。本文从AO影响东亚冬季风年代际变化的物理机制、AO对北半球冬季气温长期趋势的贡献、AO年代际影响的不确定性三个方面出发,简要回顾和总结了近年来有关年代际尺度上冬季AO时空变化及其对北半球气候影响的研究成果,并初步展望一些值得继续深入研究的问题。     

100hPa极涡、南亚高压的变化及大气环流分布特征

利用NCEP/NCAR高度场资料进行计算,对冬、夏极涡与南亚高压面积进行Morlet小波变换,并对100 hPa高度场进行EOF分解和长期趋势分析.结果表明:极涡、南亚高压具有相似的演变特征,这种相似特征在前期冬季极涡与南亚高压之间表现更为明显,体现了准5年尺度和准20年尺度的周期变化,在变化的位相上则相反.EOF分析表明,前期冬季高纬度地区与中低纬度地区的环流变化呈相反趋势,且第一模态的时间系数与前期冬季极涡的趋势一致,第一模态在一定程度上反映了前期冬季大气环流分布.夏季第一模态全场为负值,体现了夏季100 hPa整体异常性;第二模态反映了副热带中低纬度大气环流与高纬度大气环流变化相反.从其长期变化趋势来看,冬季高纬度地区的高度场呈负趋势变化,副热带地区呈正趋势变化,夏季除我国华北部分地区为负趋势变化外,均为正趋势变化.极涡、南亚高压的这种年代际变化与100 hPa高度场的长期线性趋势变化有关.