两个大气环流模式SAMIL和BCC_AGCM对北半球冬季极涡振荡的模拟对比

基于与NCEP再分析资料的比较, 本文利用大气环流模式SAMIL和北京气候中心大气环流模式BCC_AGCM的1950～1999年的AMIP试验模拟数据, 对北半球冬季环流及平流层极涡振荡的模拟性能进行了评估分析。结果表明两个模式都可以再现北半球环流基本型以及环流振荡的主导模态。对冬季气候平均态的模拟, 两个模式模拟的热带—热带外温度梯度均偏大, 极夜急流偏强, 极涡偏冷偏强;100～20 hPa平均位势高度场谐波分析表明两个模式模 拟的行星波偏弱;气候平均的10 hPa极夜急流均存在1个月的季节漂移, 200 hPa副热带西风急流较NCEP偏弱。两个模式模拟的环流变化的主导模态均代表极涡振荡, SAMIL极涡振荡的强度大于BCC_AGCM, BCC_AGCM极涡振荡的频率要高于SAMIL。连续功率谱分析表明, NCEP资料中极涡振荡存在4.6个月的显著周期, 相应地, SAMIL中为5.5个月的显著周期, BCC_AGCM中为4.8个月。NCEP资料中的极涡振荡主要发生在12～3月, SAMIL模拟的极涡振荡主要发生在2～3月, BCC_AGCM模拟的极涡振荡主要发生在2～4月。     

Changes in Winter Stratospheric Circulation in CMIP5 Scenarios Simulated by the Climate System Model FGOALS-s2

Diagnosis of changes in the winter stratospheric circulation in the Fifth Coupled Model Intercomparison Project(CMIP5) scenarios simulated by the Flexible Global Ocean-Atmosphere-Land System model,second version spectrum(FGOALS-s2),indicates that the model can generally reproduce the present climatology of the stratosphere and can capture the general features of its long-term changes during 1950-2000,including the global stratospheric cooling and the strengthening of the westerly polar jet,though the simulated polar vortex is much cooler,the jet is much stronger,and the projected changes are generally weaker than those revealed by observation data.With the increase in greenhouse gases(GHGs) effect in the historical simulation from 1850 to 2005(called the HISTORICAL run) and the two future projections for Representative Concentration Pathways(called the RCP4.5 and RCP8.5 scenarios) from 2006 to 2100,the stratospheric response was generally steady,with an increasing stratospheric cooling and a strengthening polar jet extending equatorward.Correspondingly,the leading oscillation mode,defined as the Polar Vortex Oscillation(PVO),exhibited a clear positive trend in each scenario,confirming the steady strengthening of the polar vortex.However,the positive trend of the PVO and the strengthening of the polar jet were not accompanied by decreased planetary-wave dynamical heating,suggesting that the cause of the positive PVO trend and the polar stratospheric cooling trend is probably the radiation cooling effect due to increase in GHGs.Nevertheless,without the long-term linear trend,the temporal variations of the wave dynamic heating,the PVO,and the polar stratospheric temperature are still closely coupled in the interannual and decadal time scales.     

Improved atmospheric circulation over Europe by the new generation of CMIP6 earth system models

Global Climate Models (GCMs) generally exhibit significant biases in the representation of large-scale atmospheric circulation. Even after a sensible bias adjustment these errors remain and are inherited to some extent by the derived downscaling products, impairing the credibility of future regional projections. In this study we perform a process-based evaluation of state-of-the-art GCMs from CMIP5 and CMIP6, with a focus on the simulation of the synoptic climatological patterns having a most prominent effect on the European climate. To this aim, we use the Lamb Weather Type Classification (LWT, Lamb British isles weather types and a register of the daily sequence 736 of circulation patterns 1861-1971. METEOROL OFF, GEOPHYS MEM; 737 GB; DA 1972; NO 116; PP 1-85; BIBL 2P1/2, 1972), a subjective classification of circulation weather types constructed upon historical simulations of daily mean sea level pressure. Observational uncertainty has been taken into account by considering four different reanalysis products of varying characteristics. Our evaluation unveils an overall improvement of salient atmospheric circulation features consistent across observational references, although this is uneven across models and large frequency biases still remain for the main LWTs. Some CMIP6 models attain similar or even worse results than their CMIP5 counterparts, although in most cases consistent improvements have been found, demonstrating the ability of the new models to better capture key synoptic conditions. In light of the large differences found across models, we advocate for a careful selection of driving GCMs in downscaling experiments with a special focus on large-scale atmospheric circulation aspects.

     

Winter season stratospheric circulation in the SAMIL/LASG general circulation model

In this paper, we examine the performance of the 26-level version of the SAMIL/LASG GCM (R42/L26) in simulating the seasonal cycle and perpetual winter mean stratospheric circulation as well as its variability by comparing them with the NCEP/NCAR reanalysis. The results show that the model is capable of reproducing many key features of the climatology and seasonal variation of the stratospheric circulation despite that the model’s mean polar vortex is stronger and more zonally symmetric compared to the obse...     

Extra-tropical atmospheric response to ENSO in the CMIP5 models

The seasonal mean extra-tropical atmospheric response to El Niño/Southern Oscillation (ENSO) is assessed in the historical and pre-industrial control CMIP5 simulations. This analysis considers two types of El Niño events, characterized by positive sea surface temperature (SST) anomalies in either the central equatorial Pacific (CP) or eastern equatorial Pacific (EP), as well as EP and CP La Niña events, characterized by negative SST anomalies in the same two regions. Seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the Walker circulation cell in the tropical Pacific, upper tropospheric ENSO teleconnections and the polar stratospheric response. In the CMIP5 ensembles, the magnitude of the Walker cell disruption is correlated with the strength of the mid-latitude responses in the upper troposphere i.e., the North Pacific and South Pacific lows strengthen during El Niño events. The simulated responses to El Niño and La Niña have opposite sign. The seasonal mean extra-tropical, upper tropospheric responses to EP and CP events are indistinguishable. The ENSO responses in the MERRA reanalysis lie within the model scatter of the historical simulations. Similar responses are simulated in the pre-industrial and historical CMIP5 simulations. Overall, there is a weak correlation between the strength of the tropical response to ENSO and the strength of the polar stratospheric response. ENSO-related polar stratospheric variability is best simulated in the “high-top” subset of models with a well-resolved stratosphere.     

Climatic analysis of tropopause during the northwestern Indian Ocean tropical cyclones

In this research, tropopause temperature (TT) and tropopause geopotential height (TGH) over the inner-core and environmental regions of all tropical cyclones (TCs) over the northwest of the Indian Ocean (NWIO) from 1990 to 2019 were investigated. To this aim, observational/analysis/reanalysis data and also simulated data from both historical and Representative Concentration Pathway 8.5 (RCP8.5) experiments of some global climate models (GCMs) from the Coupled Model Intercomparision Project (CMIP5) were used. Dynamical and thermo-dynamical environmental factors controlling TC, together with their correlation with different phases of some climatic indices were considered. Results indicated that the eastern part of the NWIO was more favorable for TC genesis and intensification.Lower-level stratospheric (upper-level tropospheric) cooling (warming) was detected over the NWIO during 1990−2019. Over the both inner-core and environmental regions of the NWIO TCs, the coldest tropopause occurred at a CS-Category and the warmest tropopause happened at the first stage of a VSCS event. Over the inner-core (environmental) region, the highest tropopause was detected at the first stage of a CS event (at the end of a VSCS life cycle). A significant majority of the used CMIP5 GCMs produced stratospheric cooling and tropospheric warming trends over the NWIO, similar to those obtained using ERA5 reanalysis dataset. Finally, the decreasing trend of TT over the both inner-core and environmental regions of NWIO TCs together with temperature decreasing trend obtained from the CMIP5 GCMs simulations suggest that the NWIO is prone to experience more TCs, especially the intense ones, in the future.     

Evaluating the performance of CMIP3 and CMIP5 global climate models over the north-east Atlantic region

One of the main sources of uncertainty in estimating climate projections affected by global warming is the choice of the global climate model (GCM). The aim of this study is to evaluate the skill of GCMs from CMIP3 and CMIP5 databases in the north-east Atlantic Ocean region. It is well known that the seasonal and interannual variability of surface inland variables (e.g. precipitation and snow) and ocean variables (e.g. wave height and storm surge) are linked to the atmospheric circulation patterns. Thus, an automatic synoptic classification, based on weather types, has been used to assess whether GCMs are able to reproduce spatial patterns and climate variability. Three important factors have been analyzed: the skill of GCMs to reproduce the synoptic situations, the skill of GCMs to reproduce the historical inter-annual variability and the consistency of GCMs experiments during twenty-first century projections. The results of this analysis indicate that the most skilled GCMs in the study region are UKMO-HadGEM2, ECHAM5/MPI-OM and MIROC3.2(hires) for CMIP3 scenarios and ACCESS1.0, EC-EARTH, HadGEM2-CC, HadGEM2-ES and CMCC-CM for CMIP5 scenarios. These models are therefore recommended for the estimation of future regional multi-model projections of surface variables driven by the atmospheric circulation in the north-east Atlantic Ocean region.     

BCC_AGCM2.1模式对平流层环流变化特征的数值模拟及其模式评估

使用国家气候中心大气环流模式BCC_AGCM2.1的30年模拟试验资料,对平流层纬向环流场、高空急流、极涡及爆发性增温过程进行了数值模拟研究,并使用欧洲中期天气预报中心（ECMWF）和美国国家环境预报中心（NCEP）的再分析资料对模式输出结果进行了对比、分析。结果表明：（1） 在观测海温、二氧化碳、气溶胶等外强迫地驱动下,BCC模式能够很好地再现出与再分析资料一致的平流层纬向平均风场、温度场的分布特征和季节变化过程;模拟得到的温度廓线和高空急流与再分析资料的主要差别出现在南、北半球冬季的中高纬度地区;模拟得到的平流层温度普遍偏低,主要的差异位于对流层顶区域和平流层高层。（2） 模拟的对流层上层的副热带急流位置偏南、强度也偏弱,而平流层中的绕极极夜急流则位置偏北、强度更大。这样的急流分布特征使模拟的行星波向赤道的波导更强,向极的波导偏弱;同时由于模式中本身可以形成的行星波就比再分析资料弱,因此导致模拟结果中北半球冬季的平流层极涡更加稳定、极区温度更低。（3） BCC模式对于平流层极涡的季节变化特征模拟得较好,但对强极涡扰动过程,即北半球冬季的平流层爆发性增温（SSW）事件则模拟效果不佳,不论是增温事件出现的频率,还是增温的时间、强度,模拟结果和再分析资料都还存在一定偏差,需要在今后的工作中逐步改善。     

The Indo-Australian monsoon and its relationship to ENSO and IOD in reanalysis data and the CMIP3/CMIP5 simulations

A large spread exists in both Indian and Australian average monsoon rainfall and in their interannual variations diagnosed from various observational and reanalysis products. While the multi model mean monsoon rainfall from 59 models taking part in the Coupled Model Intercomparison Project (CMIP3 and CMIP5) fall within the observational uncertainty, considerable model spread exists. Rainfall seasonality is consistent across observations and reanalyses, but most CMIP models produce either a too peaked or a too flat seasonal cycle, with CMIP5 models generally performing better than CMIP3. Considering all North-Australia rainfall, most models reproduce the observed Australian monsoon-El Niño Southern Oscillation (ENSO) teleconnection, with the strength of the relationship dependent on the strength of the simulated ENSO. However, over the Maritime Continent, the simulated monsoon-ENSO connection is generally weaker than observed, depending on the ability of each model to realistically reproduce the ENSO signature in the Warm Pool region. A large part of this bias comes from the contribution of Papua, where moisture convergence seems to be particularly affected by this SST bias. The Indian summer monsoon-ENSO relationship is affected by overly persistent ENSO events in many CMIP models. Despite significant wind anomalies in the Indian Ocean related to Indian Ocean Dipole (IOD) events, the monsoon-IOD relationship remains relatively weak both in the observations and in the CMIP models. Based on model fidelity in reproducing realistic monsoon characteristics and ENSO teleconnections, we objectively select 12 “best” models to analyze projections in the rcp8.5 scenario. Eleven of these models are from the CMIP5 ensemble. In India and Australia, most of these models produce 5–20 % more monsoon rainfall over the second half of the twentieth century than during the late nineteenth century. By contrast, there is no clear model consensus over the Maritime Continent.     

平流层极涡振荡与ENSO热带海温异常的时空联系

利用一个在等熵位涡坐标下建立的平流层极涡振荡(Polar Vortex Oscillation)指数,以及NCEP/NCAR再分析资料和NOAA_OISST_V2逐周海温资料,研究了月尺度以上热带海温异常与平流层极涡振荡的时间和空间联系,通过相关、回归以及合成分析发现,两者的显著联系主要发生在3—5年的年际时间尺度上,表现为ENSO型海温异常与极涡振荡年际趋势之间的时空关联。首先,两者的关系并不表现在同期相关上,而是当ENSO海温异常超前极涡振荡年际异常9—11个月时,两者具有最大的负相关关系。当前期热带海温偏暖(冷)时,9—11个月后极涡振荡的年际趋势为负(正)的异常,即极涡偏弱(强)或负(正)振荡事件为主。统计合成结果进一步证实,前期热带ENSO海温暖事件背景下,后期极涡振荡负事件的发生比正事件更多,强度更强,持续时间也更长,反之亦然;另外,前期热带ENSO暖海温背景下,极涡正、负振荡事件的发生均更频繁。研究连接热带ENSO海温异常与平流层极涡振荡的过程发现,热带海温异常不仅可在热带地区引起大气温度的异常响应,而且可以引发从平流层热带到极区的一系列温度异常同时向下和向极区的传播过程,并与9—11个月以后发生在极区的极涡振荡异常相联系。表明与热带海温异常相联系的极涡振荡年际异常,可能存在与季节尺度极涡振荡中类似的全球质量环流的异常变化。     

Current and future atmospheric circulation at 500 hPa over Greenland simulated by the CMIP3 and CMIP5 global models

The Greenland ice sheet is projected to be strongly affected by global warming. These projections are either issued from downscaling methods (such as Regional Climate Models) or they come directly from General Circulation Models (GCMs). In this context, it is necessary to evaluate the accuracy of the daily atmospheric circulation simulated by the GCMs, since it is used as forcing for downscaling methods. Thus, we use an automatic circulation type classification based on two indices (Euclidean distance and Spearman rank correlation using the daily 500 hPa geopotential height) to evaluate the ability of the GCMs from both CMIP3 and CMIP5 databases to simulate the main circulation types over Greenland during summer. For each circulation type, the GCMs are compared to three reanalysis datasets on the basis of their frequency and persistence differences. For the current climate (1961–1990), we show that most of the GCMs do not reproduce the expected frequency and the persistence of the circulation types and that they simulate poorly the observed daily variability of the general circulation. Only a few GCMs can be used as reliable forcings for downscaling methods over Greenland. Finally, when applying the same approach to the future projections of the GCMs, no significant change in the atmospheric circulation over Greenland is detected, besides a generalised increase of the geopotential height due to a uniform warming of the atmosphere.     

Evaluation of pan-Arctic melt-freeze onset in CMIP5 climate models and reanalyses using surface observations

The seasonal melt-freeze transitions are fundamental features of the Arctic climate system. The representation of the pan-Arctic melt and freeze onset (north of 60°N) is assessed in two reanalyses and eleven CMIP5 global circulation models (GCMs). The seasonal melt-freeze transitions are retrieved from surface air temperature (SAT) across the land and sea-ice domains and evaluated against surface observations. While monthly averages of SAT are reasonably well represented in models, large model-observation and model–model disparities of timing of melt and freeze onset are evident. The evaluation against surface observations reveals that the ERA-Interim reanalysis performs the best, closely followed by some of the climate models. GCMs and reanalyses capture the seasonal melt-freeze transitions better in the central Arctic than in the marginal seas and across the land areas. The GCMs project that during the 21st century, the summer length—the period between melt and freeze onset—will increase over land by about 1 month at all latitudes, and over sea ice by 1 and 3 months at low and high latitudes, respectively. This larger summer-length increase over sea ice at progressively higher latitudes is related to a retreat of summer sea ice during the 21st century, since open water freezes roughly 40 days later than ice-covered ocean. As a consequence, by the year 2100, the freeze onset is projected to be initiated within roughly 10 days across the whole Arctic Ocean, whereas this transition varies by about 80 days today.     

通用地球系统模式对亚洲夏季风降水的模拟能力评估

通过与观测/再分析资料和参加第五次耦合模式比较计划(CMIP5)的模式模拟结果进行对比,评估了通用地球系统模式(CESM,1.0.3版本)对亚洲夏季风降水的模拟能力。结果表明:CESM能够合理地模拟出亚洲夏季风降水的气候平均态,但与其他CMIP5模式模拟结果类似,对中国东南地区降水模拟偏少,而对中国西部高原地区降水模拟偏多;CESM可以再现亚洲季风区降水冬弱夏强、雨带北进南退的季节变化特征,其模拟偏差具有区域性和季节性差异;从EOF分析结果来看,CESM能够模拟出亚洲夏季风降水的时空变化特征,且能较好地抓住亚洲夏季风降水与厄尔尼诺-南方涛动(El Ni?o-Southern Oscillation,简称ENSO)的相关关系。总的说来,CESM对亚洲夏季风降水的模拟是合理的,模拟水平与4个最好的CMIP5模式相当。     

Assessment of the Summer South Asian High in Eighteen CMIP5 Models

The South Asian High(SAH) is one of the most important components of the Asian summer monsoon system. To understand the ability of state-of-the-art general circulation models(GCMs) to capture the major characteristics of the SAH, the authors evaluate 18 atmospheric models that participated in the Coupled Model Intercomparison Project Phase 5/Atmospheric Model Intercomparison Project(CMIP5/AMIP). Results show that the multi-model ensemble(MME) mean is able to capture the climatological pattern of the SAH, although its intensity is slightly underestimated. For the interannual variability of the SAH, the MME exhibits good correlation with the reanalysis for the area and intensity index, but poor skill in capturing the east-west oscillation of the SAH. For the interdecadal trend, the MME shows pronounced increasing trends from 1985 to 2008 for the area and intensity indexes, which is consistent with the reanalysis, but fails to capture the westward shift of the SAH center. The individual models show different capacities for capturing climatological patterns, interannual variability, and interdecadal trends of the SAH. Several models fail to capture the climatological pattern, while one model overestimates the intensity of the SAH. Most of the models show good correlations for interannual variability, but nearly half exhibit high root-mean-square difference(RMSD) values. Six models successfully capture the westward shift of the SAH center in the interdecadal trends, while other models fail. The possible causes of the systematic biases involved in several models are also discussed.     

Equatorial Atlantic variability and its relation to mean state biases in CMIP5

Coupled general circulation model (GCM) simulations participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analyzed with respect to their performance in the equatorial Atlantic. In terms of the mean state, 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial SST gradient whose sign is opposite to observations. Westerly surface wind biases in boreal spring play an important role in the reversed SST gradient by deepening the thermocline in the eastern equatorial Atlantic and thus reducing upwelling efficiency and SST cooling in the following months. Both magnitude and seasonal evolution of the biases are very similar to what was found previously for CMIP3 models, indicating that improvements have only been modest. The weaker than observed equatorial easterlies are also simulated by atmospheric GCMs forced with observed SST. They are related to both continental convection and the latitudinal position of the intertropical convergence zone (ITCZ). Particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability. The dependence of equatorial easterlies on ITCZ latitude shows a marked asymmetry. From the equator to 15°N, the equatorial easterlies intensify approximately linearly with ITCZ latitude. When the ITCZ is south of the equator, on the other hand, the equatorial easterlies are uniformly weak. Despite serious mean state biases, several models are able to capture some aspects of the equatorial mode of interannual SST variability, including amplitude, pattern, phase locking to boreal summer, and duration of events. The latitudinal position of the boreal spring ITCZ, through its influence on equatorial surface winds, appears to play an important role in initiating warm events.     

Differences between CMIP6 and CMIP5 Models in Simulating Climate over China and the East Asian Monsoon

We compare the ability of coupled global climate models from the phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6, respectively) in simulating the temperature and precipitation climatology and interannual variability over China for the period 1961–2005 and the climatological East Asian monsoon for the period1979–2005. All 92 models are able to simulate the geographical distribution of the above variables reasonably well.Compared with earlier CMIP5 models, current CMIP6 models have nationally weaker cold biases, a similar nationwide overestimation of precipitation and a weaker underestimation of the southeast–northwest precipitation gradient, a comparable overestimation of the spatial variability of the interannual variability, and a similar underestimation of the strength of winter monsoon over northern Asia. Pairwise comparison indicates that models have improved from CMIP5 to CMIP6 for climatological temperature and precipitation and winter monsoon but display little improvement for the interannual temperature and precipitation variability and summer monsoon. The ability of models relates to their horizontal resolutions in certain aspects. Both the multi-model arithmetic mean and median display similar skills and outperform most of the individual models in all considered aspects.     

ENSO stability in coupled climate models and its association with mean state

In this study, using the Bjerknes stability (BJ) index analysis, we estimate the overall linear El Niño-Southern Oscillation (ENSO) stability and the relative contribution of positive feedbacks and damping processes to the stability in historical simulations of Coupled Model Intercomparison Project Phase 5 (CMIP5) models. When compared with CMIP3 models, the ENSO amplitudes and the ENSO stability as estimated by the BJ index in the CMIP5 models are more converged around the observed, estimated from the atmosphere and ocean reanalysis data sets. The reduced diversity among models in the simulated ENSO stability can be partly attributed to the reduced spread of the thermocline feedback and Ekman feedback terms among the models. However, a systematic bias persists from CMIP3 to CMIP5. In other words, the majority of the CMIP5 models analyzed in this study still underestimate the zonal advective feedback, thermocline feedback and thermodynamic damping terms, when compared with those estimated from reanalysis. This discrepancy turns out to be related with a cold tongue bias in coupled models that causes a weaker atmospheric thermodynamical response to sea surface temperature changes and a weaker oceanic response (zonal currents and zonal thermocline slope) to wind changes.     

CMIP6模式大气中南北半球际涛动的季节循环

利用1958—2014年47个CMIP6模式输出资料和NCEP/NCAR再分析资料,研究了模式大气中南北涛动(InterHemispheric Oscillation,IHO)的季节变化特征,且评估了CMIP6对IHO季节特征的模拟能力。结果表明:47个CMIP6模式都能模拟出IHO的季节演变特征,但模式间存在一定差异。通过比较,筛选出模拟IHO季节循环较好的16个模式,它们能成功模拟出半球大气质量的时间演变和空间结构。进一步分析表明,水汽对IHO季节变化有抵消作用且半球内部水汽质量变化可驱动越赤道质量流的产生;地表净短波辐射夏高冬低,其加热造成的水汽蒸发在水汽质量变化中起到重要作用;地表净长波辐射在春秋变化幅度较大,与大气质量逐月变化吻合。对比再分析资料表明,CMIP6模式模拟的半球大气质量的峰谷值变化有明显的月份偏差,且CMIP6模式模拟的地表气压异常值的偏差主要出现在北太平洋、欧亚大陆、南半球中纬度地区和两极极区,模拟的南北半球的蒸发和降水量、赤道风场、地表净长波和短波辐射通量等均存在明显的偏差。     

Atmospheric Precursors of and Response to Anomalous Arctic Sea Ice in CMIP5 Models

This study examines pre-industrial control simulations from CMIP5 climate models in an effort to better understand the complex relationships between Arctic sea ice and the stratosphere, and between Arctic sea ice and cold winter temperatures over Eurasia. We present normalized regressions of Arctic sea-ice area against several atmospheric variables at extended lead and lag times. Statistically significant regressions are found at leads and lags, suggesting both atmospheric precursors of, and responses to, low sea ice; but generally, the regressions are stronger when the atmosphere leads sea ice, including a weaker polar stratospheric vortex indicated by positive polar cap height anomalies. Significant positive midlatitude eddy heat flux anomalies are also found to precede low sea ice. We argue that low sea ice and raised polar cap height are both a response to this enhanced midlatitude eddy heat flux. The so-called "warm Arctic, cold continents" anomaly pattern is present one to two months before low sea ice, but is absent in the months following low sea ice, suggesting that the Eurasian cooling and low sea ice are driven by similar processes. Lastly, our results suggest a dependence on the geographic region of low sea ice, with low Barents–Kara Sea ice correlated with a weakened polar stratospheric vortex, whilst low Sea of Okhotsk ice is correlated with a strengthened polar vortex. Overall, the results support a notion that the sea ice, polar stratospheric vortex and Eurasian surface temperatures collectively respond to large-scale changes in tropospheric circulation.     

Uncertainty estimation of the global temperature trends for multiple radiosondes, reanalyses, and CMIP3/IPCC climate model simulations

Based on three groups of datasets that include radiosondes, reanalyses, and climate model simulations (e.g., Coupled Model Intercomparison Project, CMIP3) from 1979 to 2008, the interannual variability, global temperature trends, and their uncertainty using ensemble spread among intra-group and inter-group datasets have been discussed. The results show that the interannual temperature variability increased from the troposphere to stratosphere, and the maximum occurs around 50?hPa. The CMIP3 climate models have the largest discrepancy in the stratosphere. The intra-group correlations at 500?hPa generally show high similarity within each data group while the inter-group correlations between reanalyses and the CMIP3 climate model simulations indicate lesser similarity. In contrast, the inter-group correlation at 50?hPa is improved except with the Japanese 25-year Reanalysis Project (JRA-25) dataset, and the Twentieth Century Reanalysis (20CR) reanalysis shows a weak cross correlation. The global temperature trends are highly dependent on the individual data sources. Compared to the radiosondes, the reanalyses show a large ensemble spread of trends in the stratosphere, and the CMIP3 climate model simulations have a large ensemble spread in the height of the crossover point where tropospheric warming changes into stratospheric cooling. The largest ensemble spread among the reanalyses in the stratosphere is mainly from the large discrepancy in the JRA-25 reanalysis after 1998 and a relatively weak anomaly in the 20CR before 1986. The largest ensemble spread among the CMIP3 climate models in the troposphere is related to the influence of both volcanic eruptions and El Ni?o/La Ni?a–Southern Oscillation events. The strong anomalies corresponding to the volcanic eruptions of El Chichon in 1982 and Mt Pinatubo in 1991 are clearly identified in the stratosphere. These volcanic eruptions reduced the warming in the troposphere and strengthened the cooling in the stratosphere during the most recent 30?years.