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1.
Releases of halocarbons into the atmosphere over the last 50 years are among the factors that have contributed to changes in the Earth’s climate since pre-industrial times. Their individual and collective potential to contribute directly to surface climate change is usually gauged through calculation of their radiative efficiency, radiative forcing, and/or Global Warming Potential (GWP). For those halocarbons that contain chlorine and bromine, indirect effects on temperature via ozone layer depletion represent another way in which these gases affect climate. Further, halocarbons can also affect the temperature in the stratosphere. In this paper, we use a narrow-band radiative transfer model together with a range of climate models to examine the role of these gases on atmospheric temperatures in the stratosphere and troposphere. We evaluate in detail the halocarbon contributions to temperature changes at the tropical tropopause, and find that they have contributed a significant warming of ~0.4 K over the last 50 years, dominating the effect of the other well-mixed greenhouse gases at these levels. The fact that observed tropical temperatures have not warmed strongly suggests that other mechanisms may be countering this effect. In a climate model this warming of the tropopause layer is found to lead to a 6% smaller climate sensitivity for halocarbons on a globally averaged basis, compared to that for carbon dioxide changes. Using recent observations together with scenarios we also assess their past and predicted future direct and indirect roles on the evolution of surface temperature. We find that the indirect effect of stratospheric ozone depletion could have offset up to approximately half of the predicted past increases in surface temperature that would otherwise have occurred as a result of the direct effect of halocarbons. However, as ozone will likely recover in the next few decades, a slightly faster rate of warming should be expected from the net effect of halocarbons, and we find that together halocarbons could bring forward next century’s expected warming by ~20 years if future emissions projections are realized. In both the troposphere and stratosphere CFC-12 contributes most to the past temperature changes and the emissions projection considered suggest that HFC-134a could contribute most of the warming over the coming century.  相似文献   

2.
Abstract

To evaluate future climate change in the middle atmosphere and the chemistry–climate interaction of stratospheric ozone, we performed a long-term simulation from 1960 to 2050 with boundary conditions from the Intergovernmental Panel on Climate Change A1B greenhouse gas scenario and the World Meteorological Organization Ab halogen scenario using the chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC). In addition to this standard simulation we performed five sensitivity simulations from 2000 to 2050 using the rerun files of the simulation mentioned above. For these sensitivity simulations we used the same model setup as in the standard simulation but changed the boundary conditions for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone-depleting substances (ODS). In the first sensitivity simulation we fixed the mixing ratios of CO2, CH4, and N2O in the boundary conditions to the amounts for 2000. In each of the four other sensitivity simulations we fixed the boundary conditions of only one of CO2, CH4, N2O, or ODS to the year 2000.

In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO2 mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH4, which also forms additional H2O in the upper stratosphere and mesosphere. Increasing N2O mixing ratios makes the smallest contributions to the cooling. The simulated ozone recovery leads to warming of the middle atmosphere.

In the EMAC model the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. The strongest contribution to this ozone production is cooling due to increasing CO2 mixing ratios, followed by increasing CH4. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NOx and HOx mixing ratios due to increased N2O and CH4 lead to intensified ozone destruction, primarily in the middle and upper stratosphere, from additional NOx; in the mesosphere the intensified ozone destruction is caused by additional HOx. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NOx is of similar importance in some regions, especially in the middle stratosphere. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport. In the polar stratosphere increased downwelling leads to additional ozone in the future, especially at high northern latitudes. The dynamical impact on ozone development is higher at some altitudes in the polar stratosphere than the ozone increase due to cooler temperatures. In the tropical lower stratosphere increased residual vertical upward transport leads to a decrease in ozone.  相似文献   

3.
Increases in chlorinated and brominated halocarbons are believed to be responsible for the depletion of stratospheric ozone observed over much of the globe in the past decade or so. Ozone depletion is in turn believed to lead to a negative radiative forcing, tending to cool the stratosphere and the surface. We show that the increasing atmospheric concentrations of ozone-depleting halocarbons and onset of related ozone depletion likely led to a negative forcing of the climate system in the 1980s that slowed significantly the rate of change of total anthropogenic radiative forcing due to the combined effect of all greenhouse gases over that decade. Within the next decade, emissions of these halocarbons are expected to rapidly decrease, with corresponding impacts on ozone and radiative forcing. As the emissions of ozone-depleting gases are reduced and eventually phased out, the rate of ozone depletion is expected to decrease and eventually reverse. All other things being equal, we show that the change from deepening ozone depletion in the 1980s to ozone increases in the future should lead to a pronounced increase in the decadal rate of change of anthropogenic greenhouse forcing of the next few decades, perhaps to levels unprecedented in this century.  相似文献   

4.
系统总结和介绍了20世纪90年代以来作者所开展的有关人类活动对东亚和中国气候影响的一系列研究活动.其中包括温室气体辐射强迫及其气候效应,大气微量气体的全球增温潜能,对流层和平流层气溶胶的辐射气候效应,气候系统外部因子对中国气候影响的总体评估,人类活动对中国和东亚地区未来气候变化的影响,以及20世纪和21世纪东亚及中国的气候变化.同时给出了一系列研究成果,这些研究成果对于正确认识和准确预测东亚地区以及中国气候变化具有十分重要的意义.  相似文献   

5.
The leading mode of southern hemisphere (SH) climatic variability, the southern annular mode (SAM), has recently seen a shift towards its positive phase due to stratospheric ozone depletion and increasing greenhouse gas (GHG) concentrations. Here we examine how sensitive the SAM (defined as the leading empirical orthogonal function of SH sea level pressure anomalies) is to future GHG concentrations. We determine its likely evolution for three intergovernmental panel on climate change (IPCC) special report on emission scenarios (SRES) for austral summer and winter, using a multi-model ensemble of IPCC fourth assessment report models which resolve stratospheric ozone recovery. During the period of summer ozone recovery (2000–2050), the SAM index exhibits weakly negative, statistically insignificant trends due to stratospheric ozone recovery which offsets the positive forcing imposed by increasing GHG concentrations. Thereafter, positive SAM index trends occur with magnitudes that show sensitivity to the SRES scenario utilised, and thus future GHG emissions. Trends are determined to be strongest for SRES A2, followed by A1B and B1, respectively. The winter SAM maintains a similar dependency upon GHG as summer, but over the entire twenty-first century and to a greater extent. We also examine the influence of ozone recovery by comparing results to models that exclude stratospheric ozone recovery. Projections are shown to be statistically different from the aforementioned results, highlighting the importance of ozone recovery in governing SAM-evolution. We therefore demonstrate that the future SAM will depend both upon GHG emissions and stratospheric ozone recovery.  相似文献   

6.
气候变化的归因与预估模拟研究   总被引：14，自引：2，他引：12  
本文总结了近五年来中国科学院大气物理研究所在气候变暖的归因模拟与预估研究上的主要进展。研究表明,利用海温、太阳辐射和温室气体等实际强迫因子驱动大气环流模式,能够较为合理地模拟全球平均地表气温在20世纪的演变,但是难以模拟出包括北大西洋涛动／北极涛动和南极涛动在内的高纬度环流的长期变化趋势。利用温室气体和硫酸盐气溶胶等“历史资料”驱动气候系统模式,能够较好地模拟出20世纪后期的全球增暖,但如果要再现20世纪前期(1940年代)的变暖,还需同时考虑太阳辐射等自然外强迫因子。20世纪中国气温演变的耦合模式模拟技巧,较之全球平均情况要低;中国气候在1920年代的变暖机理目前尚不清楚。对于近50年中国东部地区“南冷北暖”、“南涝北旱”的气候变化,基于大气环流模式特别是区域气候模式的数值试验表明,夏季硫酸盐气溶胶的负辐射效应超过了温室气体的增暖效应,从而对变冷产生贡献。但现有的数值模拟证据,不足以说明气溶胶增加对“南涝北旱”型降水异常有贡献。20世纪中期以来,青藏高原主体存在明显增温趋势,温室气体浓度的增加对这种增暖有显著贡献。多模式集合预估的未来气候变化表明,21世纪全球平均温度将继续增暖,增温幅度因不同排放情景而异;中国大陆年均表面气温的增暖与全球同步,但增幅在东北、西部和华中地区较大,冬季升温幅度高于夏季、日最低温度升幅要强于日最高温度;全球增暖有可能对我国中东部植被的地理分布产生影响。伴随温室气体增加所导致的夏季平均温度升高,极端温度事件增多;在更暖的气候背景下,中国大部分地区总降水将增多,极端降水强度加大且更频繁发生,极端降水占总降水的比例也将增大。全球增暖有可能令大洋热盐环流减弱,但是减弱的幅度因模式而异。全球增暖可能不是导致北太平洋副热带－热带经圈环流自20世纪70年代以来变弱的原因。文章同时指出了模式预估结果中存在的不确定性。  相似文献   

7.
郭艳君  王国复 《气象学报》2019,77(6):1073-1085
基于118站探空资料研究了近60年中国850—100 hPa气温变化趋势及季节和区域特征,并通过与1979—2017年卫星微波气温的对比研究了中国探空气温均一化的不确定性。研究表明,1958—2017年中国平均对流层气温呈上升趋势,300 hPa升温最为显著,平流层下层（100 hPa）为降温趋势。冬季对流层上层升温趋势和夏季平流层下层降温趋势较强。1979—2017年较整个时段对流层升温趋势较强,平流层下层降温趋势较弱。青藏高原和西北地区对流层上层升温趋势较强。通过与卫星微波气温和邻近探空站探空气温的对比以及均一化前后日夜气温差值检测出中国探空均一化气温仍残存非均一性问题。由于参照序列的局限性,均一化未能完全去除21世纪最初10年中国探空系统变化造成的对流层中、上层至平流层下层气温系统性下降的影响,导致中国对流层上层升温趋势被低估和平流层下层降温趋势被高估。未来可通过参考卫星微波气温和邻近探空站序列调整非均一性订正顺序并增加合理性检验等方法改进中国探空气温均一化方案。   相似文献   

8.
两类极区平流层异常增温的特征及其与850hPa温度的关系   总被引：1，自引：0，他引：1  
采用NCEP/NCAR逐日再分析资料,将冬季极区平流层增温分为两种类型:Ⅰ型和Ⅱ型,并分析了两种类型增温的特征、机制及其与850hPa温度的关系。结果表明,波动强迫的强度和对流层的热量能否向上到达平流层是决定两类平流层异常增温的两个主要因素。Ⅰ型平流层增温期间,对流层也表现出了明显的增温特征,850hPa与平流层温度距平场呈现相当正压结构,极区和中纬度异常表现为反位相的振荡,呈现典型的北极涛动的特征;Ⅱ型平流层异常增温期间,增温异常仅局限在平流层范围内,平流层的中低层与高层呈现反位相的距平分布,850hPa温度距平场呈现无规则的分布特征。  相似文献   

9.
Temperature trends in the upper stratosphere are investigated using satellite measurements from Stratospheric Sounding Unit(SSU) outputs and simulations from chemistry–climate models(CCMs) and the Coupled Model Intercomparison Project Phase 6(CMIP6). Observational evidence shows a lack of cooling in the Antarctic, in contrast to strong cooling at other latitudes, during austral winter over 1979–97. Analysis of CCM simulations for a longer period of1961–97 also shows a significant contrast in the...  相似文献   

10.
Wilhelm May 《Climate Dynamics》2008,31(2-3):283-313
In this study, concentrations of the well-mixed greenhouse gases as well as the anthropogenic sulphate aerosol load and stratospheric ozone concentrations are prescribed to the ECHAM5/MPI-OM coupled climate model so that the simulated global warming does not exceed 2°C relative to pre-industrial times. The climatic changes associated with this so-called “2°C-stabilization” scenario are assessed in further detail, considering a variety of meteorological and oceanic variables. The climatic changes associated with such a relatively weak climate forcing supplement the recently published fourth assessment report by the IPCC in that such a stabilization scenario can only be achieved by mitigation initiatives. Also, the impact of the anthropogenic sulphate aerosol load and stratospheric ozone concentrations on the simulated climatic changes is investigated. For this particular climate model, the 2°C-stabilization scenario is characterized by the following atmospheric concentrations of the well-mixed greenhouse gases: 418 ppm (CO2), 2,026 ppb (CH4), and 331 ppb (N2O), 786 ppt (CFC-11) and 486 ppt (CFC-12), respectively. These greenhouse gas concentrations correspond to those for 2020 according to the SRES A1B scenario. At the same time, the anthropogenic sulphate aerosol load and stratospheric ozone concentrations are changed to the level in 2100 (again, according to the SRES A1B scenario), with a global anthropogenic sulphur dioxide emission of 28 TgS/year leading to a global anthropogenic sulphate aerosol load of 0.23 TgS. The future changes in climate associated with the 2°C-stabilization scenario show many of the typical features of other climate change scenarios, including those associated with stronger climatic forcings. That are a pronounced warming, particularly at high latitudes accompanied by a marked reduction of the sea-ice cover, a substantial increase in precipitation in the tropics as well as at mid- and high latitudes in both hemispheres but a marked reduction in the subtropics, a significant strengthening of the meridional temperature gradient between the tropical upper troposphere and the lower stratosphere in the extratropics accompanied by a pronounced intensification of the westerly winds in the lower stratosphere, and a strengthening of the westerly winds in the Southern Hemisphere extratropics throughout the troposphere. The magnitudes of these changes, however, are somewhat weaker than for the scenarios associated with stronger global warming due to stronger climatic forcings, such as the SRES A1B scenario. Some of the climatic changes associated with the 2°C-stabilization are relatively strong with respect to the magnitude of the simulated global warming, i.e., the pronounced warming and sea-ice reduction in the Arctic region, the strengthening of the meridional temperature gradient at the northern high latitudes and the general increase in precipitation. Other climatic changes, i.e., the El Niño like warming pattern in the tropical Pacific Ocean and the corresponding changes in the distribution of precipitation in the tropics and in the Southern Oscillation, are not as markedly pronounced as for the scenarios with a stronger global warming. A higher anthropogenic sulphate aerosol load (for 2030 as compared to the level in 2100 according to the SRES A1B scenario) generally weakens the future changes in climate, particularly for precipitation. The most pronounced effects occur in the Northern Hemisphere and in the tropics, where also the main sources of anthropogenic sulphate aerosols are located.  相似文献   

11.
To analyze the mechanism by which water vapor increase leads to cooling in the stratosphere, the effects of water-vapor increases on temperature in the stratosphere were simulated using the two-dimensional, interactive chemical dynamical radiative model (SOCRATES) of NCAR. The results indicate that increases in stratospheric water vapor lead to stratospheric cooling, with the extent of cooling increasing with height, and that cooling in the middle stratosphere is stronger in Arctic regions. Analysis of the radiation process showed that infrared radiative cooling by water vapor is a pivotal factor in middle-lower stratospheric cooling. However, in the upper stratosphere (above 45 km), infrared radiation is not a factor in cooling; there, cooling is caused by the decreased solar radiative heating rate resulting from ozone decrease due to increased stratospheric water vapor. Dynamical cooling is important in the middle-upper stratosphere, and dynamical feedback to temperature change is more distinct in the Northern Hemisphere middle-high latitudes than in other regions and signiffcantly affects temperature and ozone in winter over Arctic regions. Increasing stratospheric water vapor will strengthen ozone depletion through the chemical process. However, ozone will increase in the middle stratosphere. The change in ozone due to increasing water vapor has an important effect on the stratospheric temperature change.  相似文献   

12.
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。  相似文献   

13.
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.  相似文献   

14.
This paper examines in detail the statement in the 2007 IPCC Fourth Assessment Report that “Most of the observed increase in global average temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations”. We use a quantitative probabilistic analysis to evaluate this IPCC statement, and discuss the value of the statement in the policy context. For forcing by greenhouse gases (GHGs) only, we show that there is a greater than 90 % probability that the expected warming over 1950–2005 is larger than the total amount (not just “most”) of the observed warming. This is because, following current best estimates, negative aerosol forcing has substantially offset the GHG-induced warming. We also consider the expected warming from all anthropogenic forcings using the same probabilistic framework. This requires a re-assessment of the range of possible values for aerosol forcing. We provide evidence that the IPCC estimate for the upper bound of indirect aerosol forcing is almost certainly too high. Our results show that the expected warming due to all human influences since 1950 (including aerosol effects) is very similar to the observed warming. Including the effects of natural external forcing factors has a relatively small impact on our 1950–2005 results, but improves the correspondence between model and observations over 1900–2005. Over the longer period, however, externally forced changes are insufficient to explain the early twentieth century warming. We suggest that changes in the formation rate of North Atlantic Deep Water may have been a significant contributing factor.  相似文献   

15.
温室气体和硫酸盐气溶胶的辐射强迫作用   总被引：5，自引：4，他引：5  
对GOALS4 .0海 陆 气耦合模式的相关部分进行了改进 ,主要改进包括温室气体的扩充和硫酸盐气溶胶“显式”方案的引入 ,并引入 2 0世纪温室气体的实际浓度变化以及硫循环模式模拟的硫酸盐气溶胶的三维全球浓度分布 ,模拟了温室气体和硫酸盐气溶胶造成的辐射强迫的空间分布和时间变化。全球平均的温室气体和硫酸盐气溶胶的辐射强迫分别为 2 .17W /m2 和 - 0 .2 9W /m2 ;温室气体造成的辐射强迫在空间上呈现明显的纬向结构 ,最大值 (大于 2 .5W/m2 )和最小值 (小于 1W /m2 )分别位于副热带和两极地区 ,在北半球主要工业区硫酸盐气溶胶的辐射强迫绝对值接近温室气体的辐射强迫值 (大于 - 2 .0W /m2 )。  相似文献   

16.
工业革命以来,大气中温室气体不断增加,驱动了全球变暖。IPCC第五次评估报告(AR5)指出,人类排放的温室气体导致的地球系统能量增加中90%以上都被海洋吸收,使得海洋增暖,海洋热含量增加。IPCC最新发布的《气候变化中的海洋和冰冻圈特别报告》(SROCC)发现：自1970年以来,几乎确定海洋上层2000 m在持续增暖。1993—2017年间的增暖速率至少为1969—1993年的2倍,体现出显著的变暖增强趋势。此外,在20世纪90年代以后,2000 m以下的深海也已观测到了变暖信号,尤其是在南大洋(30°S以南)。在1970—2017年间,南大洋上层2000 m储存了全球海洋约35%~43%的热量,在2005—2017年期间增加到45%~62%。基于耦合气候模型预估,几乎可确定海洋将在21世纪持续增暖,2018—2100年间海洋热含量上升幅度可能是1970—2017年间的5~7倍(RCP8.5情景)或2~4倍(RCP2.6情景)。变暖导致的热膨胀效应贡献了1993年以来全球海平面上升的约43%。  相似文献   

17.
Abstract

A coupled 1‐D radiative‐convective and photochemical diffusion model is used to study the influence of ozone photochemistry on changes in the vertical temperature structure and surface climate resulting from the doubling of atmospheric CO2, N2O, CH4 and increased stratospheric aerosols owing to the El Chichón volcanic eruption. It is found when CO2 alone is doubled, that the total ozone column increases by nearly 6% and the resulting increase in the solar heating contributes a smaller temperature decrease in the stratosphere (up to 4 K near the stratopause level). When the concentration of CO2, N2O and CH4 are simultaneously doubled, the total ozone column amount increases by only 2.5% resulting in a reduced temperature recovery in the stratosphere. Additional results concerning the effect of the interaction of ozone photochemistry with the stratospheric aerosol cloud produced by the El Chichón eruption show that it leads to a reduction in stratospheric ozone, which in turn has the effect of increasing the cooling at the surface and above the cloud centre while causing a slight warming below in the lower stratosphere.  相似文献   

18.
IPCC AR6报告解读：水循环变化   总被引：1，自引：0，他引：1  
水循环在全球和区域气候变化中扮演重要角色,与全球变暖背景下水循环变化密切相关的淡水资源短缺、副热带干旱区扩张、极端旱涝灾害频发等问题日益突出,严重制约生态系统和人类社会的可持续发展。在IPCC第六次评估报告中,第一工作组首次单独设立一章,即第八章,用于系统性评估全球水循环变化。评估显示,自20世纪中叶以来,人类活动已经显著地改变了全球水循环,包括大气湿度和降水强度的整体性增加,全球干旱模态改变,南半球风暴轴向极地移动等。已经发生的水循环变化受到温室气体、气溶胶、土地利用在内的多种人类强迫的影响,而未来全球水循环变化将逐渐由温室气体主导。  相似文献   

19.
As the global climate warms due to increasing greenhouse gases, the regional climate of the Gulf of Mexico and Caribbean region will also change. This study presents the latest estimates of the expected changes in temperature, precipitation, tropical cyclone activity, and sea level. Changes in temperature and precipitation are derived from climate model simulations produced for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), by comparing projections for the mid- and late-21st century to the late 20th century and assuming a “middle-of-the-road” scenario for future greenhouse gas emissions. Regional simulations from the North America Regional Climate Change Program (NARCCAP) are used to corroborate the IPCC AR4 rainfall projections over the US portion of the domain. Changes in tropical cyclones and sea level are more uncertain, and our understanding of these variables has changed more since IPCC AR4 than in the case of temperature and precipitation. For these quantities, the current state of knowledge is described based on the recent peer-reviewed literature.  相似文献   

20.
The frequent coincidence of volcanic forcing with El Niño events disables the clear assignment of climate anomalies to either volcanic or El Niño forcing. In order to select the signals, a set of four different perpetual January GCM experiments was performed (control, volcano case, El Niño case and combined volcano/El Niño case) and studied with advanced statistical methods for the Northern Hemisphere winter. The results were compared with observations. The signals for the different forcings are discussed for three variables (temperature, zonal wind and geopotential height) and five levels (surface, 850 hPa, 500 hPa, 200 hPa and 50 hPa). The global El Niño signal can be selected more clearly in the troposphere than in the stratosphere. In contrast, the global volcano signal is strongest in the stratospheric temperature field. The amplitude of the perturbation for the volcano case is largest in the Atlantic region. The observed effect of local cooling due to the volcanic reduction of shortwave radiation over large land areas (like Asia) in subtropical regions, the observed advective warming over Eurasia and the advective cooling over Greenland are well simulated in the model. The radiative cooling near the surface is important for the volcano signal in the subtropics, but it is weak in high latitudes during winter. A statistically significant tropospheric signal of El Niño forcing occurs in the subtropics and in the midlatitudes of the North Pacific. The local anomalies in the El Niño forcing region in the tropics, and the warming over North America in middle and high latitudes are simulated as observed. The combined signal is different from a simple linear combination of the separate signals. It leads to a climate perturbation stronger than for forcing with El Niño or stratospheric aerosol alone and to a somewhat modified pattern.  相似文献   

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