平流层爆发性增温及其影响研究进展

平流层爆发性增温(stratospheric sudden warming,SSW)是冬季平流层大气环流结构的一种突变现象,在短时间内平流层中高纬度的温度、风和极涡都会发生剧烈变化。因此,SSW也就成为平流层大气环流及其变化研究的重要方面之一。在强SSW期间,高纬地区温度急剧升高,西风被东风取代,极涡几乎全部崩溃。SSW极大地影响着北半球对流层大气,甚至整个中高层大气,包括对平流层乃至中层大气微量气体分布的重要影响。随着临近空间飞行平台的研究应用,以及由此而提出的临近空间环境条件的保障问题,作为临近空间重要组成部分的平流层环流变化将更加引起人们的关注。本文就SSW的特征、发生机制、对上下层相互作用的重要影响,以及SSW与准两年振荡、ENSO等的密切关系和SSW的数值模拟等方面的研究工作,进行了回顾和总结。     

A two-way stratosphere-troposphere coupling of submonthly zonal-mean circulations in the Arctic

This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particular emphasis on interactive stratosphere-troposphere processes. The submonthly variability is identified and measured using a daily NAM index, which concentrates primarily on zonally symmetrical circulation. A schematic lifecycle of submonthly variability is developed that reveals a two-way coupling pro- cess between the stratosphere and troposphere in the NH polar region. Specifically, anomalous tropospheric zonal winds in the Atlantic and Pacific sectors of the Arctic propagate upwards to the low stratosphere, disturbing the polar vortex, and resulting in an anomalous stratospheric geopotential height （HGT） that subsequently propagates down into the troposphere and changes the sign of the surface circulations. From the standpoint of planetary-scale wave activities, a feedback loop is also evident when the anoma- lous planetary-scale waves （with wavenumbers 2 and 3） propagate upwards, which disturbs the anomalous zonally symmetrical flow in the low stratosphere, and induces the anomalous HGT to move poleward in the low stratosphere, and then propagates down into the troposphere. This increases the energy of waves at wavenumbers 2 and 3 in the low troposphere in middle latitudes by enhancing the land-sea contrast of the anomalous HGT field. Thus, this study supports the viewpoint that the downward propagation of stratospheric NAM signals may not originate in the stratosphere.     

涡动在南北半球平流层极涡崩溃过程中作用的比较

比较了南北半球春季平流层极涡的崩溃过程以及涡动在此崩溃过程中的作用。极涡的崩溃时间以平流层极夜急流核区最后一次西风转换为东风的时间来确定。结果表明南北半球平流层极涡的崩溃过程有着共同的特点,涡动和非绝热加热过程都对极涡的崩溃起着重要的作用,在极涡崩溃前平流层行星尺度波动活动明显,极涡崩溃以后,这种波动活动便迅速减弱。其中从对流层上传的行星波决定着极涡的具体崩溃时间。两个半球的差别主要表现在南半球极涡崩溃过程一般始于平流层高层,然后逐渐下传,而北半球这种下传不是很明显。其次,北半球平流层极涡崩溃偏晚年,极涡的减弱有两次过程,第一次为快速变化过程,第二次变化比较缓慢,而南半球平流层极涡崩溃无论早晚年只有一次减弱过程。长期的变化趋势分析表明南北半球平流层极涡的崩溃时间逐渐推迟,特别是20世纪90年代中后期以来,这种推迟更加明显。进一步的研究还发现,伴随着平流层极涡的崩溃过程平流层和对流层存在强烈的动力耦合,南北半球极涡迅速减弱前,各自半球的环状模指数也由负指数增加为正指数,表明低层环流对于平流层极涡的崩溃起到重要的作用;同时极涡不同强度所对应的低层环状模指数也不同,这可能与不同强度平流层极涡对于上传的行星波的反射有关。     

北半球平流层大气环流转型的基本气候特征

利用1948—2009年NCEP/NCAR逐日高度场和风场再分析资料探讨了平流层各主要层次上环流转型的年际、年代际时空演变特征。结果表明:北半球平流层冬季环流转为夏季环流的过程是高层环流转型早,低层环流转型晚,但在各层次上环流转型早晚存在着区域性差异。自新地岛到西伯利亚北部地区的环流转型最早,且该区域与北半球环流平均转型时间的年际以及年代际特征最相近。北半球平流层环流转型的气候平均时间早于东亚热带季风爆发时间,从而可能成为季风预测的前兆信号。分析还得到平流层各主要层次环流转型时间具有明显的年代际特征,环流转型时间呈现由偏晚到偏早、又从偏早到偏晚的变化特征,只是年代际转折年份在不同区域、不同层次存在差异。此外,平流层环流转型时间普遍存在准2年、准3~6年、准9~12年以及准21~24年的周期,可能与气候系统其他成员有密切联系。     

Interaction of atmospheric chemistry and climate and its impact on stratospheric ozone

The interactively coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM is employed in sensitivity calculations to investigate feedback mechanisms of dynamic, chemical, and radiative processes. Two multi-year model simulations are carried out, which represent recent atmospheric conditions. It is shown that the model is able to reproduce observed features and trends with respect to dynamics and chemistry of the troposphere and lower stratosphere. In polar regions it is demonstrated that an increased persistence of the winter vortices is mainly due to enhanced greenhouse gas mixing ratios and to reduced ozone concentration in the lower stratosphere. An additional sensitivity simulation is investigated, concerning a possible future development of the chemical composition of the atmosphere and climate. The model results in the Southern Hemisphere indicate that the adopted further increase of greenhouse gas mixing ratios leads to an intensified radiative cooling in the lower stratosphere. Therefore, Antarctic ozone depletion slightly increases due to a larger PSC activity, although stratospheric chlorine is reduced. Interestingly, the behavior in the Northern Hemisphere is different. During winter, an enhanced activity of planetary waves yields a more disturbed stratospheric vortex. This "dynamical heating" compensates the additional radiative cooling due to enhanced greenhouse gas concentrations in the polar region. In connection with reduced stratospheric chlorine loading, the ozone layer clearly recovers.     

CFSv2 prediction skill of stratospheric temperature anomalies

This study evaluates the prediction skill of stratospheric temperature anomalies by the Climate Forecast System version 2 (CFSv2) reforecasts for the 12-year period from January 1, 1999 to December 2010. The goal is to explore if the CFSv2 forecasts for the stratosphere would remain skillful beyond the inherent tropospheric predictability time scale of at most 2 weeks. The anomaly correlation between observations and forecasts for temperature field at 50 hPa (T50) in winter seasons remains above 0.3 over the polar stratosphere out to a lead time of 28 days whereas its counterpart in the troposphere at 500 hPa drops more quickly and falls below the 0.3 level after 12 days. We further show that the CFSv2 has a high prediction skill in the stratosphere both in an absolute sense and in terms of gain over persistence except in the equatorial region where the skill would mainly come from persistence of the quasi-biennial oscillation signal. We present evidence showing that the CFSv2 forecasts can capture both timing and amplitude of wave activities in the extratropical stratosphere at a lead time longer than 30 days. Based on the mass circulation theory, we conjecture that as long as the westward tilting of planetary waves in the stratosphere and their overall amplitude can be captured, the CFSv2 forecasts is still very skillful in predicting zonal mean anomalies even though it cannot predict the exact locations of planetary waves and their spatial scales. This explains why the CFSv2 has a high skill for the first EOF mode of T50, the intraseasonal variability of the annular mode while its skill degrades rapidly for higher EOF modes associated with stationary waves. This also explains why the CFSv2’s skill closely follows the seasonality and its interannual variability of the meridional mass circulation and stratosphere polar vortex. In particular, the CFSv2 is capable of predicting mid-winter polar stratosphere warming events in the Northern Hemisphere and the timing of the final polar stratosphere warming in spring in both hemispheres 3–4 weeks in advance.     

Observational evidence of the delayed response of stratospheric polar vortex variability to ENSO SST anomalies

The temporal and spatial relationship between ENSO and the extratropical stratospheric variability in the Northern Hemisphere is examined. In general, there exists a negative correlation between ENSO and the strength of the polar vortex, but the maximum correlation is found in the next winter season after the mature phase of ENSO event, rather than in the concurrent winter. Specifically, the stratospheric polar vortex tends to be anomalously warmer and weaker in both the concurrent and the next winter season following a warm ENSO event, and vice versa. However, the polar anomalies in the next winter are much stronger and with a deeper vertical structure than that in the concurrent winter. Our analysis also shows that, the delayed stratospheric response to ENSO is characterized with poleward and downward propagation of temperature anomalies, suggesting an ENSO-induced interannual variability of the global mass circulation in the stratosphere. Particularly, in response to the growing of a warm ENSO event, there exist warm temperature and positive isentropic mass anomalies in the midlatitude stratosphere since the preceding summer. The presence of an anomalous wavenumber-1 in the concurrent winter, associated with an anomalous Aleutian high, results in a poleward extension of warm anomalies into the polar region, and thus a weaker stratospheric polar vortex. However, the midlatitude warm temperature and positive isentropic mass anomalies persist throughout the concurrent winter till the end of the next summer. In comparison with the concurrent winter, the strengthening of poleward heat transport by an anomalous wavenumber-2 in the next winter results in a much warmer and weaker polar vortex accompanied with a colder midlatitude stratosphere.     

Involvement of the Brewer–Dobson circulation in changes of stratospheric temperature and ozone

Wintertime temperature and ozone in the Northern Hemisphere stratosphere vary significantly between years. Largely random, those variations are marked by compensating changes at high and low latitudes, a feature that reflects the residual mean circulation of the stratosphere. Interannual changes of temperature and ozone each track anomalous forcing of the residual circulation. This relationship is shown to be obeyed even over the Arctic, where transport is augmented by heterogeneous chemical processes that destroy ozone. Chlorine activation obeys a similar relationship, reflecting feedback between changes of the residual circulation and anomalous photochemistry.Changes of stratospheric dynamical and chemical structure are found be accompanied by coherent changes in the troposphere. Vertically extensive, they reflect inter-dependent changes in the stratosphere and troposphere, which are coupled by the residual circulation through transfers of mass. The corresponding structure is shown to share major features with empirical modes of interannual variability associated with the AO and its cousin, the NAO.A 3D model of dynamics and photochemistry is used to simulate anomalous temperature and ozone. Driven by anomalous wave activity representative of that observed, the model reproduces the salient structure of observed interannual changes. Anomalous temperature and ozone follow in the integrations from anomalous downwelling, which, under disturbed conditions, renders temperature over the Arctic anomalously warm, and from anomalous poleward transport, which renders Arctic ozone anomalously rich.Accompanying random interannual changes in the observed record was a systematic decline of Northern Hemisphere temperature and ozone during the 1980s and early 1990s. Comprising decadal trends, these systematic changes are shown to have the same essential structure and seasonality as random changes, which, in turn, vary coherently with anomalous forcing of the residual circulation. Implications of the findings to the interpretation of stratospheric trends are discussed in light of anomalous residual motion, photochemistry, and feedback between them.     

平流层臭氧变化对对流层气候影响的研究进展

平流层对对流层的作用是准确评估、预测对流层气候变化的一个重要方面。其中平流层成分尤其是臭氧的变化,可以改变平流层乃至对流层的辐射平衡,从而影响平流层、对流层的热动力过程。本文从辐射、动力2个角度介绍了平流层臭氧影响对流层气候变化的若干研究进展。平流层臭氧可以通过长短波辐射的方式对对流层大气造成辐射强迫,利用大气化学气候模式可以定量计算平流层臭氧变化引起的辐射强迫,但是辐射强迫的估算受模式中辐射传输模块本身缺陷的影响存在不确定性。动力方面,平流层臭氧变化产生的辐射效应可以改变温度的垂直和经向梯度,造成波折射指数的变化,进而影响平流层甚至对流层内波的折射与反射,通过上对流层下平流层区域内的波—流相互作用,对对流层气候产生影响。另外,南极臭氧损耗可通过大气环状模影响冬春季中高纬度对流层的天气气候,但是其影响的强度大小以及物理机制仍需进一步的确认。值得注意的是,北极平流层臭氧的变化与北半球中高纬度气候变化之间的关系相比南半球要更加复杂,需要更为深入的研究。     

Observed and simulated precursors of stratospheric polar vortex anomalies in the Northern Hemisphere

The Northern Hemisphere stratospheric polar vortex is linked to surface weather. After Stratospheric Sudden Warmings in winter, the tropospheric circulation is often nudged towards the negative phase of the Northern Annular Mode (NAM) and the North Atlantic Oscillation (NAO). A strong stratospheric vortex is often associated with subsequent positive NAM/NAO conditions. For stratosphere?Ctroposphere associations to be useful for forecasting purposes it is crucial that changes to the stratospheric vortex can be understood and predicted. Recent studies have proposed that there exist tropospheric precursors to anomalous vortex events in the stratosphere and that these precursors may be understood by considering the relationship between stationary wave patterns and regional variability. Another important factor is the extent to which the inherent variability of the stratosphere in an atmospheric model influences its ability to simulate stratosphere?Ctroposphere links. Here we examine the lower stratosphere variability in 300-year pre-industrial control integrations from 13 coupled climate models. We show that robust precursors to stratospheric polar vortex anomalies are evident across the multi-model ensemble. The most significant tropospheric component of these precursors consists of a height anomaly dipole across northern Eurasia and large anomalies in upward stationary wave fluxes in the lower stratosphere over the continent. The strength of the stratospheric variability in the models was found to depend on the variability of the upward stationary wave fluxes and the amplitude of the stationary waves.     

北半球冬季行星波的传播及其输运作用

利用变换欧拉平均方程讨论了行星波动力学。观测和模拟结果都表明,在北半球冬季准定常行星波的经向传播存在两支波导。一支为高纬度波导,另一支则为低纬度波导。这些结果与理论分析相当一致。通过对EP通量进一步的研究表明,平流层爆发性增温是沿高纬度波导传播的异常行星波与平均气流相互作用的结果。而热带风场的准两年周期振荡（QBO）是低纬度平流层下层大气纬向平均流的一个重要年际变化,它可以影响行星波沿低纬度波导的传播;此外,由一个行星波一平均流耦合模式模拟的结果表明,这个热带风场的变化还可以通过波流相互作用调制行星波沿高纬度波导的传播。 行星波对臭氧的输运作用在文中也进行了分析。行星波强迫出的剩余平均环流表明,耗散的行星波有强的输运作用;向北的涡动热量输送可以强迫出一个正的输运环流,其在低纬度上升并在高纬度下沉。同时研究还表明,热带风场的QBO对行星波传播的调制对输运环流也有重要影响,模式结果表明,在QBO的东风位相期间行星波引起的输运作用明显增强,其结果可用于解释平流层高纬度臭氧的年际变化。     

北半球极区平流层冬季12月与1—2月气候变化形势的对比

根据1980—2000年ERA-Interim再分析的风场和温度场资料,计算12月与1—2月北半球行星波的EP通量及其散度,并按冬季不同月份分析了平流层整层温度和风场从20世纪80年代到90年代变化的特征及其与行星波活动变化的关系。结果表明,12月高纬度地区中低平流层呈增温趋势;而1—2月温度变化呈冷却趋势。在12月中高纬度中上平流层纬向风明显减速;而在1—2月高纬度中高平流层,随着纬度和高度的增加,纬向风呈明显加速趋势。冬季北半球行星波主要沿低纬度和极地波导两支波导向上传播。但是,12月行星波沿低纬度波导的传播减弱,沿极地波导向平流层整层的传播则明显增强。而1—2月行星波沿低纬度波导的传播明显增强,沿极地波导向平流层的传播则减弱。因此,北半球极区平流层1980—2000年间12月与1—2月波流相互作用的年代际变化形势趋于相反,有必要针对冬季不同月份分开进行讨论。     

Dust Storms in North China in 2002： A Case Study of the Low Frequency Oscillation

The low frequency oscillation in both hemispheres and its possible role in the dust weather storm events over North China in 2002 are analyzed as a case study. Results show that the Aleutian Low is linked with the Circumpolar Vortex in the Southern Hemisphere on a 30-60-day oscillation, with a weak Circumpolar Vortex tending to deepen the Aleutian Low which may be helpful for the generation of dust storm events. The possible mechanism behind this is the inter-hemispheric interaction of the mean meridional circulation, with the major variability over East Asia. The zonal mean westerly wind at high latitudes of the Southern Hemisphere in the upper level troposphere may lead that of the Northern Hemisphere, which then impacts the local circulation in the Northern Hemisphere. Thus, the low frequency oscillation teleconnection is one possible linkage in the coupling between the Southern Hemisphere circulation and dust events over North China. However, the interannual variation of the low frequency oscillation is unclear.     

A review of the temporal and spatial variability of Arctic and Antarctic atmospheric circulation based upon ERA-40

A survey of the spatial and temporal behavior of the atmospheric general circulation as it relates to both polar regions is presented. The review is based on the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-year reanalysis (ERA-40), updated using ECMWF operational analyses. The analysis spans 1960–2005 in the Northern Hemisphere, but is restricted to 1979–2005 in the Southern Hemisphere because of difficulties experienced by ERA-40 prior to the modern satellite era.The seasonal cycle of atmospheric circulation is illustrated by focusing on winter and summer. The huge circulation contrasts between the land-dominated Northern Hemisphere and the ocean-dominated Southern Hemisphere stand out. The intensification of the North Atlantic Oscillation/Northern Annular Mode and the Southern Annular Mode in DJF is highlighted and likely due to warming of the tropical Indian Ocean. The Arctic frontal zone during northern summer and the semi-annual oscillation throughout the year in the Southern Hemisphere are prominent features of the high latitude circulation in the respective hemispheres.Rotated principal component analysis (RPCA) is used to describe the primary modes of temporal variability affecting both polar regions, especially the links with the tropical forcing. The North Atlantic Oscillation is a key modulator of the atmospheric circulation in the North Atlantic sector, especially in winter, and is the dominant control on the moisture transport into the Arctic Basin. The Pacific-South American teleconnection patterns are primary factors in the high southern latitude circulation variability throughout the year, especially in the Pacific sector of Antarctica where the majority of moisture transport into the continent occurs.     

Midlatitude Mesosphere/Lower Thermosphere Region Winds and Their Connection with European and Asian Tropospheric Parameters

Summary Investigation of long-term measurements of winter mesosphere/lower thermosphere (MLT) region zonal winds has shown a connection of northern hemisphere tropospheric parameters and MLT conditions. These are on one hand due to a connection of the stratospheric polar vortex and the North Atlantic Oscillation (NAO) and on the other hand forced by a coupling of the troposphere/lower stratosphere and the MLT region through planetary wave propagation and wave-mean flow interaction. The connection between European and Asian winter climatological parameters and the NAO leads to the fact, that the signal of Eurasian winter conditions can be found in the interannual variability of MLT winds. Some of these winter tropospheric parameters influence the strength of the Indian monsoon in the following summer, and this leads to a correlation between winter MLT winds and summer Indian rainfall, so that the midlatitude MLT winter dynamics can be used as a precursory signal of the strength of the Indian monsoon. Received July 21, 1998 Revised November 1, 1999     

Stratospheric circulation in seasonal forecasting models: implications for seasonal prediction

Accurate seasonal forecasts rely on the presence of low frequency, predictable signals in the climate system which have a sufficiently well understood and significant impact on the atmospheric circulation. In the Northern European region, signals associated with seasonal scale variability such as ENSO, North Atlantic SST anomalies and the North Atlantic Oscillation have not yet proven sufficient to enable satisfactorily skilful dynamical seasonal forecasts. The winter-time circulations of the stratosphere and troposphere are highly coupled. It is therefore possible that additional seasonal forecasting skill may be gained by including a realistic stratosphere in models. In this study we assess the ability of five seasonal forecasting models to simulate the Northern Hemisphere extra-tropical winter-time stratospheric circulation. Our results show that all of the models have a polar night jet which is too weak and displaced southward compared to re-analysis data. It is shown that the models underestimate the number, magnitude and duration of periods of anomalous stratospheric circulation. Despite the poor representation of the general circulation of the stratosphere, the results indicate that there may be a detectable tropospheric response following anomalous circulation events in the stratosphere. However, the models fail to exhibit any predictability in their forecasts. These results highlight some of the deficiencies of current seasonal forecasting models with a poorly resolved stratosphere. The combination of these results with other recent studies which show a tropospheric response to stratospheric variability, demonstrates a real prospect for improving the skill of seasonal forecasts.     

Progress in Research of Stratosphere-Troposphere Interactions： Application of Isentropic Potential Vorticity Dynamics and the Effects of the Tibetan Plateau

This paper reviews recent progress in understanding isentropic potential vorticity （PV） dynamics during interactions between the stratosphere and troposphere, including the spatial and temporal propagation of circulation anomalies associated with the winter polar vortex oscillation and the mechanisms of stratosphere- troposphere coupling in the global mass circulation framework. The origins and mechanisms of interannual variability in the stratospheric circulation are also reviewed. Particular attention is paid to the role of the Tibetan Plateau as a PV source （via its thermal forcing） in the global and East Asian atmospheric circulation. Diagnosis of meridional isentropic PV advection over tile Tibetan Plateau and East Asia indicates that the distributions of potential temperature and PV over the east flank of the Tibetan Plateau and East Asia favor a downward and southward isentropic transport of high PV from the stratosphere to the troposphere. This transport manifests the possible influence of the Tibetan Plateau on the dynamic coupling between the stratosphere and troposphere during summer, and may provide a new framework for understanding the climatic effects of the Tibetan Plateau.     

北半球准定常行星波气候平均态的资料分析和数值模拟

利用NCEP/NCAR再分析资料和大气环流模式(CCSR/NIES AGCM Ver 5.6),对北半球准定常行星波的气候平均态分布进行分析和模拟.再分析资料分析的结果表明:北半球冬季,准定常行星波沿两支波导向上传播,其中一支在对流层上层转向中低纬度传播,另外一支折向高纬度,通过极地波导上传到平流层.其中,1波和2波可以上传到平流层,因而其振幅分布除在中低纬的对流层上层出现一个次大值外,在高纬度平流层中上层会出现一个最大值,3波则主要限制在对流层,其振幅分布除在副热带对流层上层出现一个次大值外,最大值出现在中纬度对流层上层.北半球夏季,整个平流层为东风环流,极地波导不存在,行星波不能上传到平流层,在对流层活动也较弱,1波、2波、3波的传播情况大致相似,表现为在对流层上层由中纬度向赤道地区的传播.相应的振幅分布是,对1波和2波而言,最大值出现在中低纬对流层顶附近,同时在中高纬对流层上层出现一个次大值,而3波的振幅分布正好相反,最大值出现在中高纬对流层上层,次大值则在中低纬对流层顶附近.利用大气环流模式进行的数值模拟表明,模式可以比较好地模拟冬夏季准定常行星波的传播路径,但模拟的北半球冬季沿极地波导向平流层的传播明显偏弱,其结果是对1波、2波而言,高纬度平流层中上层的振幅最大值明显小于再分析资料的数值.文中还讨论了数值模拟与资料分析中行星波的差异可能对大气环流模拟的影响.     

热带加热异常影响冬季平流层极涡强度的数值模拟

本文利用大气环流模式SAMIL/LASG,通过选择两种对流参数化方案,研究了热带加热异常对热带外平流层模拟的影响。结果表明,因不同对流参数化方案引起的热带对流加热状况的差异,可显著影响模式对北半球冬季平流层极涡强度的模拟偏差。与采用Manabe对流参数化方案相比,采用Tiedtke参数化方案可以显著改善对平流层极涡强度的模拟,使平流层极涡“过强”及极区“过冷”的模拟偏差得到明显改善。研究其中的影响过程发现,由于Manabe方案最大凝结潜热加热高度过低,在对流层中低层;而Tiedtke方案的最大凝结潜热加热位置在对流层中上层,因而Tiedtke(Manabe)方案时热带大气温度在对流层中上层较为偏暖(偏冷),在平流层低层较为偏冷(偏暖)。自秋季开始,与热带对流层高层温度的暖偏差相联系,热带外对流层高层以及热带平流层低层出现伴随的温度冷偏差;与之对应,平流层中纬度从秋季开始也出现持续的温度暖偏差。另外,随着秋冬季节平流层行星波活动的出现,Tiedtke方案时热带外地区行星波1波的强度也明显强于Manabe方案,使得秋冬季节涡动引起的向极热通量在Tiedtke方案时明显偏强,从而造成了冬季平流层极区温度偏暖、极涡强度偏弱。     

Response of the Météo-France climate model to changes in CO2 and sea surface temperature

The climate response to an increase in carbon dioxide and sea surface temperatures is examined using the Météo-France climate model. This model has a high vertical resolution in the stratosphere and predicts the evolution of the ozone mixing ratio. This quantity is fully interactive with radiation and photochemical production and loss rates are accounted for. Results from a 5-year control run indicate a reasonable agreement with observed climatologies. A 5-year simulation is performed with a doubled CO₂ concentration using, as lower boundary conditions, mean surface temperatures anomalies and sea ice limits predicted for the years 56–65 of a 100-year transient simulation performed at Hamburg with a global coupled atmosphere-ocean model. The perturbed simulation produces a global mean surface air warming of 1.4 K and an increase in global mean precipitation rate of 4%. Outside the high latitudes in the Northern Hemisphere, the model simulates a strong cooling in the stratosphere reaching 10 K near the stratopause. Temperature increases are noticed in the lower polar stratosphere of the Northern Hemisphere caused by an intensification in the frequency of sudden warmings in the perturbed simulation. The low and mid-latitude stratospheric cooling leads to an ozone column enhancement of about 5%. Other features present in similar studies are exhibited in the troposphere such as the stronger surface warming over polar regions of the Northern Hemisphere, the summer time soil moisture drying in mid-latitudes and the increase in high convective cloudiness in tropical regions.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil Correspondence to: JF Mahfouf