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。     

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.     

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.     

On the Differences and Climate Impacts of Early and Late Stratospheric Polar Vortex Breakup

The stratospheric polar vortex breakup (SPVB) is an important phenomenon closely related to the seasonal transition of stratospheric circulation. In this paper, 62-year NCEP/NCAR reanalysis data were employed to investigate the distinction between early and late SPVB. The results showed that the anomalous circulation signals extending from the stratosphere to the troposphere were reversed before and after early SPVB, while the stratospheric signals were consistent before and after the onset of late SPVB. Arctic Oscillation (AO) evolution during the life cycle of SPVB also demonstrated that the negative AO signal can propagate downward after early SPVB. Such downward AO signals could be identified in both geopotential height and temperature anomalies. After the AO signal reached the lower troposphere, it influenced the Aleutian Low and Siberian High in the troposphere, leading to a weak winter monsoon and large-scale warming at mid latitudes in Asia. Compared to early SPVB, downward propagation was not evident in late SPVB. The high-latitude tropospheric circulation in the Northern Hemisphere was affected by early SPVB, causing it to enter a summer circulation pattern earlier than in late SPVB years.     

Three-dimensional dynamic features of two arctic oscillation types

We investigated the differences between stratospheric (S-type) and tropospheric (T-type) Arctic Oscillation (AO) events on the intraseasonal time scale, in terms of their influences on surface air temperature (SAT) over the Northern Hemisphere and the dynamic features associated with their spatial structures. S-type AO events showed a stratosphere-troposphere coupled structure, while T-type events exhibited a stratosphere-troposphere uncoupled structure. The annular SAT anomalies over the Northern Hemisphere were found to be associated with S-type AO events, whereas such an annular feature was substantially destructed in T-type AO events. The different horizontal structures in the troposphere of the two types could mainly be attributed to transient eddy feedback forcing. As for the vertically uncoupled structure of Ttype events, the underlying dynamical features that differentiate them from S-type events lie in the vertical propagation of zonally confined Rossby waves. In T-type events, the zonally confined Rossby wave packets can emanate from the significant height anomalies over Northeast Asia, where one vertical waveguide exists, and then propagate upward into the stratosphere. In contrast, such a vertical propagation was not evident for S-type events. The stratospheric anomalies associated with the upward injection of the zonally confined Rossby waves from the troposphere in T-type events can further induce the anomalous vertical propagation of planetary waves (PWs) through the interference between the climatological-mean PWs and anomalous PWs, leading to the final stratosphere-troposphere uncoupled structure of T-type events.     

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.     

Simulation of the Effect of Water-vapor Increase on Temperature in the Stratosphere

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.     

平流层异常下传对2009年12月北半球大范围降雪过程的影响

2009年12月北半球中纬度出现大范围持续低温、暴风雪等天气。采用NCEP／NCAR再分析资料研究了平流层AO（Arctic Oscillation,北极涛动）异常信号下传的特征及其对本次极端气候事件的影响,并讨论了与平流层异常信号下传相关的行星波活动。结果表明：1）与此次极端气候事件相联系的负位相A0异常11月首先发生在平流层,维持将近1个月后于12月初开始下传,并且迅速传至地面。12月整个对流层的位势高度及温度在极区附近出现强的正异常,而中纬度地区则为负异常。2）平流层AO异常信号下传后,地面出现有利于低温降雪过程的环流异常。12月上旬,亚洲大陆东部及北美大陆西部出现异常偏北风,造成了俄罗斯、北美西部大面积负的温度异常;12月中下旬,欧洲大陆盛行偏西北气流,同时蒙古高压增强,欧亚大陆北部包括中国北方出现大片负的温度异常。3）在此次极端气候事件之前,北半球高纬度地区有异常强的行星波上传至平流层,导致平流层出现负位相的AO异常,并维持了一个月;随后,上传到平流层的行星波减弱,同时平流层负位相的AO异常迅速传至地面,导致了有利于低温降雪的环流异常。     

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。     

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.     

Link between Arctic ozone and the stratospheric polar vortex

The stratospheric ozone layer protects life on earth by preventing solar ultraviolet radiation from reaching the surface. Owing to the large population in the Northern Hemisphere and extreme ozone loss in the Arctic, changes in Arctic stratospheric ozone (ASO) and their causes have attracted broad attention recently. Using monthly mean data during the period 1980–2020 from MERRA-2, the relationship between the stratospheric polar vortex (SPV) and ASO, along with the relative contributions of chemical and dynamic processes associated with the SPV to changes in ASO, were examined in this study. Results showed that the ASO in March has a strong out-of-phase link with the strength of the SPV in March, with no obvious lead–lag correlations, i.e., an increase (decrease) in ASO corresponds to a weakened (strengthened) SPV. Further analysis suggested that the strong out-of-phase link between the SPV and ASO is related to changes in Brewer–Dobson circulation (BDC). Strong SPV events, accompanied by a low temperature condition and weakened upward propagation of planetary waves over the Arctic in the stratosphere, result in weakened BDC. The weakened downwelling at high latitudes tends to transport less ozone-rich air in the upper stratosphere at lower latitudes into the lower stratosphere at high latitudes, facilitating a decrease in ASO. The BDC's vertical velocity plays the dominant role in modulating ASO.摘要利用1980–2020年MERRA-2资料, 分析了平流层极涡 (Stratospheric polar vortex, SPV) 和北极臭氧 (Arctic stratospheric ozone, ASO) 的关系, 评估了与SPV相关的化学, 动力过程在其中的相对作用. 结果表明, 3月份ASO与同期SPV强度反相关最大. SPV-ASO二者反相关与平流层剩余环流 (Brewer-Dobson circulation, BDC) 变化密切相关. 强SPV伴随的北极平流层低温条件和行星波向上传播减弱, 导致BDC减弱, 减弱的BDC下沉支将低纬度平流层上层臭氧含量较低的空气输送到北极平流层低层, 从而导致ASO减少. BDC垂直速度在其中起主导作用.     

Simulating the effects of the 1991 Mount Pinatubo volcanic eruption using the ARPEGE atmosphere general circulation model

The climate changes that occured following the volcanic eruption of Mount Pinatubo in the Phillippines on 15 June 1991 have been simulated using the ARPEGE atmosphere general circulation model （AGCM）. The model was forced by a reconstructed spatial-time distribution of stratospheric aerosols intended for use in long climate simulations. Four statistical ensembles of the AGCM simulations with and without volcanic aerosols over a period of 5 years following the eruption have been made, and the calculated fields have been compared to available observations. The model is able to reproduce some of the observed features after the eruption, such as the winter warming pattern that was observed over the Northern Hemisphere （NH） during the following winters. This pattern was caused by an enhanced Equator-to-pole temperature gradient in the stratosphere that developed due to aerosol heating of the tropics. This in turn led to a strengthening of the polar vortex, which tends to modulate the planetary wave field in such a way that an anomalously positive Arctic Oscillation pattern is produced in the troposphere and at the surface, favouring warm conditions over the NH. During the summer, the model produced a more uniform cooling over the NH.     

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.     

两类极区平流层异常增温的特征及其与850hPa温度的关系

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。     

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.     

平流层-对流层相互作用研究进展：等熵位涡理论的应用及青藏高原影响

系统介绍了近年来应用等熵位涡理论研究平流层-对流层动力相互作用所发现的一些新的事实和机理,包括平流层冬季极涡振荡过程中平流层、对流层环流异常的时空传播特征,以及等熵质量理论框架下的平流层-对流层动力耦合机理,还介绍了影响平流层环流年际尺度异常的因子及影响过程。回顾了夏季青藏高原的热力作用所激发的负位涡强迫源对东亚及全球大气环流的影响。并基于对夏季高原周边等熵位涡经向输送垂直分布的诊断进一步说明,夏季青藏高原的存在使高原东缘及东亚地区成为平流层和对流层物质交换的独特区域,探讨了夏季青藏高原影响平流层-对流层动力耦合的一种重要途径及其影响全球气候的重要意义。     

北半球平流层极涡崩溃早晚的环流特征及其对5月南亚降水的影响

本文采用1979—2014年NCEP/NCAR月平均再分析资料、CMAP和GPCP月平均降水资料,分析了北半球平流层极涡崩溃早晚的环流特征及其与南亚降水的关系。结果表明,北半球平流层极涡崩溃时间存在明显的年际变化特征。极涡崩溃偏早(偏晚)年,自3月开始异常信号从平流层向下传播,之后的4月,从平流层到对流层高层极区温度异常偏高(偏低),极涡异常偏弱(偏强),极夜急流异常偏弱(偏强)。结果还表明,5月南亚降水异常与平流层极涡崩溃时间的早晚存在显著相关,5月南亚降水异常与平流层极涡崩溃早晚年平流层异常信号的下传有关。当平流层极涡崩溃偏晚年,4月平流层极区表现为位势高度异常偏低,而中纬度则位势高度场异常偏高,并伴随位势高度异常场的向下传播,5月该位势高度异常场下传至阿拉伯海北部大陆上空对流层顶,形成有利于降水的环流场,导致南亚降水偏多。反之,则相反。     

东亚太平洋地区近地面臭氧的季节和年际变化特征及其与东亚季风的关系

利用东亚清洁背景站近地面臭氧观测资料,结合风场和降水资料,分析东亚各地区臭氧的多年季节变化特征,并探讨东亚太平洋地区臭氧的季节和年际变化与季风的关系以及影响近地层臭氧的主要因子。结果表明：东亚大部分地区与北半球背景站观测一致,近地层臭氧季节变化表现为春季最高、夏季最低的特征;但在东亚中纬度33～43°N,臭氧表现为夏季最高,而在东亚20°N以南地区臭氧则表现为冬末、春初最高。东亚太平洋沿岸近地面臭氧的季节变化主要受东亚冬、夏季风环流的季节变化控制。该地区不同纬度上春季峰值出现时间的差异与亚洲大陆春季不同时期污染物输送路径的差异有关。对东亚太平洋沿岸对流层顶附近位势涡度、高空急流和垂直环流季节变化的分析表明,冬春季可能是平流层向对流层输送的最强期,对近地面臭氧贡献最大。初夏至秋季（5-11月）,平流层向对流层输送较弱,对近地面臭氧贡献较小。东亚太平洋地区夏季风爆发的时间和强度以及季风环流型的年际差异是导致该地区春、夏季臭氧年际变化的主要原因;而季风降水和云带位置以及平流层一对流层交换是造成臭氧年际变化的其他原因。     

The cause of the spring strengthening of the Antarctic polar vortex

The stratospheric polar vortex strengthening from late winter to spring plays a crucial role in polar ozone depletion. The Arctic polar vortex reaches its peak intensity in mid-winter, whereas the Antarctic vortex usually strengthens in early spring. As a result, the strong ozone depletion is observed every year over the Antarctic, while over the Arctic short-term ozone loss occasionally occurs in late winter or early spring. However, the cause of such a difference in the life cycles of the Arctic and Antarctic polar vortices is still not completely clear. Based on the ERA-Interim reanalysis data, we show a high agreement between the seasonal variations of temperature in the subtropical lower stratosphere and zonal wind in the subpolar and polar lower stratosphere in the Southern Hemisphere. Thus, the spring strengthening of the Antarctic polar vortex can occur due to the seasonal temperature increase in the subtropical lower stratosphere in this period.     

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。