气溶胶对青藏高原气候变化影响的数值模拟分析

利用美国大气研究中心(NCAR)提供的2组数值试验结果对比,分析了只考虑温室气体增加(1%CO2试验)和综合考虑大气温室气体与气溶胶持续增加(50yrs试验)条件下,青藏高原地区地表温度、积雪深度及其他气候要素的变化,并在此基础上探讨了大气气溶胶含量变化对高原气候变化的可能影响.分析结果表明:只考虑大气CO2含量每年增加1%的变化时,青藏高原相对邻近地区地表温度显著增加,春、夏、秋及冬季地表温度线性增温率均表现出随着海拔高度升高而增强.例如,在海拔1.5～2 km,3～3.5 km和4.5～5 km范围内对应的冬季增温趋势分别为0.29 ℃/10 a,0.36 ℃/10 a和0.50 ℃/10 a.在温室气体引起的高原增暖过程中地表积雪深度普遍降低,且高海拔地区的积雪减少愈加明显.当综合考虑气溶胶和温室气体含量共同增加时,青藏高原地表增暖相对偏弱,春、夏和秋季增温也随海拔高度上升而加强,但冬季地面增温幅度随海拔上升反而下降,海拔1.5～2 km,3～3.5km和4.5～5 km范围内对应的冬季增温趋势分别为0.02 ℃/10 a,-0.03 ℃/10 a和-0.13 ℃/10 a.对比分析发现,大气气溶胶增加造成青藏高原冬季增温不明显甚至出现变冷趋势,地面积雪也随之增多,这可能歪曲了青藏高原地区气候变暖对海拔高度的依赖性.     

青藏高原地区气溶胶直接辐射强迫的数值模拟研究

通过比较EMAC模式模拟结果和卫星观测结果证实了模式的可信性,进而利用模拟结果分析研究了2010～2012年青藏高原上空气溶胶光学厚度及其直接辐射强迫的时空分布规律。结果表明:所有气溶胶组分中,沙尘、水溶性气溶胶和气溶胶中液态水是高原的主要消光物质,三者年平均消光占比分别为0.27、0.20和0.49。2011年夏季纳布罗火山爆发,高空气溶胶消光在海拔14 km以上显著增强。青藏高原气溶胶在大气顶和地表的直接辐射强迫分布总体上由北向南递减,沙尘气溶胶在高原北部边缘大气顶产生正辐射强迫,气溶胶大气层直接辐射强迫对大气有增温效应,主要出现在沙尘含量高的地区。此外,受纳布罗火山爆发的影响,平流层气溶胶在2011年秋、冬季产生了明显较强的负辐射强迫,相比于无火山爆发的2010年和 2012年,青藏高原上空平流层气溶胶负辐射强迫在2011年秋季和冬季分别增加了55.50%和52.38%。     

欧亚大陆夏季地表温度的气候特征及与大气环流的联系

采用1960—2010年NCEP/NCAR逐月再分析资料,利用经验正交函数(EOF)展开方法等,分析了欧亚大陆夏季地表温度变化特征及其与大气环流的关系。结果表明:欧亚大陆夏季地表温度的均方差在高纬度地区大于在低纬度地区。欧亚大陆夏季地表温度最主要的特征是全区一致变化,除了青藏高原东侧为降温趋势外,其他地区为变暖趋势,其中40~65°N增温明显;其次,高纬度地区表现出"-+-"变化特征。西风环流指数的变化与地表温度的增温密切相关,而EU指数与中高纬度地区地表温度异常的分布类型密切相关。根据欧亚大陆夏季地表温度的气候特征和时空变化特征,确定了5个关键区。各关键区指数都有增温趋势,但是变化特征不同。不同关键区指数的异常所对应的环流形势异常均不相同,与不同关键区地表温度密切联系的环流因子也不相同。     

全球变暖背景下青藏高原夏季大气中水汽含量的变化特征

利用中国气象局提供的0. 5°×0. 5°降水和温度的日值资料,联合ERA-Interim、MERRA2(second M odern-Era Retrospective analysis for Research and Applications)和JRA-55(Japanese 55-year Reanalysis)再分析资料以及全球陆面数据同化系统(Global Land surface Data Asimilation System,GLDAS-2. 0)资料,研究了全球变暖背景下青藏高原夏季地表气温及降水的变化特征,以及该地区大气中水汽含量及水汽输送特征。结果表明,1979—1998年期间,高原的地表气温呈增加趋势,降水呈减少趋势;而在全球增温减缓期间(1999—2010年),地表气温及降水较1979—1998年期间呈现更为显著的增加趋势。在青藏高原上空,大气中水汽含量在1979—2010年间整体呈增加趋势;然而,进一步分析表明,在此期间由外界向高原输送的水汽逐年降低,尤其在1998年后,由于西南季风强度的大幅减弱,使得外界向高原的净水汽输送量减少得更为显著;青藏高原地表蒸散量的分析表明,自1998年后,高原地表的蒸散量显著增加,成为高原地区大气中水汽增加的主要原因。     

1979—2014年全球变暖背景下青藏高原气候变化特征

近几十年来全球变暖受到越来越广泛的关注,然而全球变暖从1998年开始趋缓,但青藏高原却呈现加速增暖的趋势。本文基于前人研究,系统回顾了青藏高原气温、积雪、降水和大气热源等四方面在全球变暖背景下的变化,指出高原的加速增温导致了积雪迅速融化,降水明显增多的同时,高原热源却呈现减弱趋势。     

近50年中国东部夏季降水与贝加尔湖地表气温年代际变化的关系

最近50年全球变暖,陆地增温幅度大于海洋,主要的增温中心位于亚洲北部、欧洲和北美等地区。因此,全球变暖有可能通过改变大尺度季风环流而影响中国气候变化。利用美国国家航空航天局空间研究中心(GISS)的逐月地表气温资料、NCEP/NCAR再分析资料及中国604个站逐月气温和降水观测资料,重点讨论了1951—2007年中国东部夏季降水与同期的北半球大陆地表气温年代际尺度变化关系。结果表明,近50年中国东部夏季降水异常主要表现为南旱北涝与南涝北旱两者年代际异常之间的转换,但在1996年之后,伴随北方干旱区向南发展,呈现出华北和长江中下游地区降水同时减少的特征。研究发现中国华北地区夏季降水与同期的环贝加尔湖地表气温在年代际尺度上存在显著的负相关关系;贝加尔湖地区地表气温增暖可能导致蒙古高原对流层出现异常的暖性反气旋,使得位于蒙古高原的气旋频数减少和强度减弱。由于华北降水与蒙古气旋的活动直接相关,从而导致华北地区夏季降水的持续性减少。自1996年开始贝加尔湖地区的地表气温进一步升高,导致中国北方干旱化加剧。由于环贝加尔湖地区是过去50年全球变暖的最显著地区之一,因此,全球变暖可能是通过关键区域的温度变化对中国的气候变化产...     

气候变化的归因与预估模拟研究

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。     

近54年中国地面气温变化

采用国家基准气候站和基本气象站地面月平均气温资料,在严格质量控制和非均一性订正的基础上,分析了1951年以来中国大陆地区近地表年和季节平均气温演化的时间与空间特征.结果表明,我国近54年来年平均地表气温变暖幅度约为1.3℃,增温速率接近0.25℃/10 a,比全球或半球同期平均增温速率高得多.全国大范围增暖主要发生在近20余年.气温变化的季节差异和空间特征与前人分析结论基本一致,冬季增温速率高达0.39℃/10 a,春季为0.28℃/10 a,秋季0.20℃/10 a,夏季增温速率最小,但也达到0.15℃/10 a.我国20世纪80年代初期开始的明显增暖主要表现在冷季,但进入90年代以来夏季增暖也日趋明显.从区域上看,中国大陆地区最明显的增温发生在北方和青藏高原地区,而西南的四川盆地和云贵高原北部仍维持弱的降温趋势.值得提出的是,作者给出的结果尚未考虑城镇化对地面气温观测记录的影响.     

中国地区春季沙尘气溶胶短波辐射气候效应数值模拟研究

利用耦合了起沙模型(MEDM)的区域气候模式RegCM3,模拟研究了2000年春季中国地区沙尘气溶胶短波辐射气候效应。结果表明,春季中国沙尘气溶胶垂直负荷的大值区主要位于南疆盆地和阿拉善高原。引入沙尘气溶胶后,中国地区地表均出现负的辐射强迫,地面气温普遍降低,中低层(400 hPa层以下)大气温度则呈上升趋势。沙尘源区及其下游地区总云量及降水主要呈减少趋势,云量与降水的分布特征与空中流场的变化趋势一致性较好。     

1979年夏季青藏高原地区大气加热场特征

本文用1979年夏季6—8月青藏高原地区17个站资料（包括青藏高原科学实验资料），通过直接法求得长波辐射、短波辐射、凝结潜热和感热输送等四项加热分量，在此基础上求出高原地区的平均大气热量输送，并和国内外其它作者所估计的高原大气热源情况进行比较。计算结果表明，对高原大气热源的主要贡献是长波辐射，文中还探讨了青藏高原地区大气加热场与高原季风爆发前后以及高原季风活跃和中断时期环流的关系。     

Simulated Influence of the Atlantic Multidecadal Oscillation on Summer Eurasian Nonuniform Warming since the Mid-1990s

Based on ensemble experiments with three atmospheric general circulation models(AGCMs), this study investigates the role of the Atlantic Multidecadal Oscillation(AMO) in shaping the summer nonuniform warming over the Eurasian continent since the mid-1990 s. The results validate that the positive-phase AMO can indeed cause nonuniform warming,with predominant amplified warming over Europe–West Asia and Northeast Asia, but with much weaker warming over Central Asia. The underlying mechanism is then diagnosed from the perspective that the boundary forcing modulates the intrinsic atmospheric variability. The results highlight the role of the Silk Road Pattern(SRP), an intrinsic teleconnection pattern across the subtropical Eurasian continent propagating along the Asian jet. The SRP can not only be identified from the AGCM control experiments with the climatological sea surface temperature(SST), but can also be simulated by the AMO-related SST anomaly(SSTA) forcing. Furthermore, diagnostic linear baroclinic model experiments are conducted, and the results suggest that the SRP can be triggered by the AMO-related tropical diabatic heating. The AMO-triggered SRP-like responses feature anticyclonic circulations over Europe–West Asia and Northeast Asia, but cyclonic circulation over Central Asia. These responses cause increased warm advection towards Europe–West Asia and Northeast Asia, reduced precipitation and cloud cover, and then increased downward shortwave radiation. This increased warm advection and increased downward shortwave radiation together cause amplified warming in Europe–West Asia and Northeast Asia. The situation is opposite for Central Asia.     

Abrupt summer warming and changes in temperature extremes over Northeast Asia since the mid-1990s: Drivers and physical processes

This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990 s. Observations indicate an abrupt increase in summer mean surface air temperature(SAT) over Northeast Asia since the mid-1990 s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature(Tmax), daily minimum temperature(Tmin), annual hottest day temperature(TXx), and annual warmest night temperature(TNx) were observed. There were also increases in the frequency of summer days(SU) and tropical nights(TR).Atmospheric general circulation model experiments forced by changes in sea surface temperature(SST)/ sea ice extent(SIE),anthropogenic greenhouse gas(GHG) concentrations, and anthropogenic aerosol(AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes,although the abrupt decrease in precipitation since the mid-1990 s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA(through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990 s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease.     

Comparative Analysis of the Mechanisms of Intensified Summer Warming over Europe-West Asia and Northeast Asia since the Mid-1990s through a Process-based Decomposition Method

Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid-1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two regions remains unclear. In this study, we compared the individual contributions of influential factors for amplified warming over these two regions through a quantitative diagnostic analysis based on CFRAM (climate feedback-response analysis method). The changes in surface air temperature are decomposed into the partial changes due to radiative processes (including CO2concentration, incident solar radiation at the top of the atmosphere, surface albedo, water vapor content, ozone concentration, and clouds) and non-radiative processes (including surface sensible heat flux, surface latent heat flux, and dynamical processes). Our results suggest that the enhanced warming over these two regions is primarily attributable to changes in the radiative processes, which contributed 0.62 and 0.98 K to the region-averaged warming over Europe-West Asia (1.00 K) and Northeast Asia (1.02 K), respectively. Among the radiative processes, the main drivers were clouds, CO2concentration, and water vapor content. The cloud term alone contributed to the mean amplitude of warming by 0.40 and0.85 K in Europe-West Asia and Northeast Asia, respectively. In comparison, the non-radiative processes made a much weaker contribution due to the combined impact of surface sensible heat flux, surface latent heat flux, and dynamical processes, accounting for only 0.38 K for the warming in Europe-West Asia and 0.05 K for the warming in Northeast Asia.The resemblance between the influential factors for the amplified warming in these two separate regions implies a common dynamical origin. Thus, this validates the possibility that they originate from the Silk Road pattern.     

A decadal shift of summer surface air temperature over Northeast Asia around the mid-1990s

This study identifies a decadal shift of summer surface air temperature （SAT） over Northeast Asia,including southeastern parts of Russia,Mongolia and northern China,around the mid-1990s.The results suggest that the SAT over the Northeast Asia experienced a significant warming after 1994 relative to that before 1993.This decadal shift also extends to northern China,and leads to a warmer summer over Northeast China and North China after the mid-1990s.The decadal warming over Northeast Asia is found to concur with the enhancement of South China rainfall around the mid-1990s.On the one hand,both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift only in summer,but not in other seasons.On the other hand,both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift not only in the summer seasonal mean,but also in each month of summer （June,July and August）.Furthermore,the decadal warming is found to result from an anticyclonic anomaly over Northeast Asia,which can be interpreted as the response to the increased precipitation over South China,according to previous numerical results.Thus,we conclude that the warming shift of summer Northeast Asian SAT around the mid-1990s was a remote response to the increased precipitation over South China.     

Abnormal Warming of the Summer Surface Air Temperature in Central Asia from 1980 to 2019北大核心CSCD

This work analyzes the abrupt change in summer surface air temperature (SAT) in Central Asia (CA) and its relationship with sea surface temperature (SST) in the North Atlantic and snow cover in the Qinghai Tibet Plateau between 1980 and 2019 based on NCEP/NCAR reanalysis data, CRU SAT, and snow cover and global SST data. The results reveal a significant summer SAT change in CA in 2005. The standardized regional average temperature index in CA shifts from the previous negative phase to the subsequent positive phase, indicating a significant summer SAT increase in CA. Analysis of the anomalous atmospheric circulations related to interdecadal changes in summer SAT in CA shows the abnormally enhanced anticyclonic circulation system in the west of CA after 2005. The atmospheric subsidence associated with the anomalous anticyclone can cause warming. On the other hand, the reduction in the amount of cloud caused by this anticyclone anomaly enhancement results in the increase in downward short-wave radiation and thus is favorable for the increased summer temperature in CA. Furthermore, the interdecadal summer SAT changes in CA in 2005 are closely related to SST warming in the middle and high latitudes of the North Atlantic and the reduction in snow cover in the west of the Tibet Plateau (TP). The SST increase in the middle and high latitudes of the North Atlantic can stimulate a Rossby wave propagating downstream. The reduction in snow cover in the west of the TP can cause warming to the above atmosphere through the snow albedo effect. The changes in both the North Atlantic SST and the TP snow can strengthen the anticyclone over CA, leading to an abnormally high summer SAT over there. © 2023 Science Press. All rights reserved.     

Possible effect of the Tibetan Plateau on the “upstream” climate over West Asia,North Africa,South Europe and the North Atlantic

We conduct several experiments using a fully-coupled climate model to understand the role of Tibetan Plateau (TP) surface heating in the climate variations over West Asia, South Europe, North Africa, and the North Atlantic during summer. Emphasis has been placed on the physical processes and responsible mechanisms that involve the shift of the Hadley cell and the important features of rotational and divergent response of the atmosphere to the TP heating. The relative importance of the TP to the Asian continent is also analyzed. A heating of the TP surface leads to local increases in tropospheric temperature and the thickness of the air column due to the so-called air pumping effect. In the upper troposphere, the South Asian high intensifies and extends westward. To the west of TP, especially in West Asia, South Europe, North Africa, and the North Atlantic, distinguished Rossby wave responses to the TP heating occur with anomalous high pressure and uniform warming in the entire troposphere. Correspondingly, descending motions intensify and precipitation decreases. However, the tropical Sahel rainfall increases because of a northward shift of the Atlantic intertropical convergence zone and the anomalous westerlies due to the weakening of the southeastern portion of the Atlantic subtropical high. These effects of the TP heating explain a remarkable portion of the effects by the Asian continent heating. In addition, the impacts of different magnitudes of TP surface heating are also discussed.

     

A modeling study of the effects of aerosols on clouds and precipitation over East Asia

The National Center for Atmospheric Research Community Atmosphere Model (version 3.5) coupled with the Morrison?CGettelman two-moment cloud microphysics scheme is employed to simulate the aerosol effects on clouds and precipitation in two numerical experiments, one representing present-day conditions (year?2000) and the other the pre-industrial conditions (year?1750) over East Asia by considering both direct and indirect aerosol effects. To isolate the aerosol effects, we used the same set of boundary conditions and only altered the aerosol emissions in both experiments. The simulated results show that the cloud microphysical properties are markedly affected by the increase in aerosols, especially for the column cloud droplet number concentration (DNC), liquid water path (LWP), and the cloud droplet effective radius (DER). With increased aerosols, DNC and LWP have been increased by 137% and 28%, respectively, while DER is reduced by 20%. Precipitation rates in East Asia and East China are reduced by 5.8% and 13%, respectively, by both the aerosol??s second indirect effect and the radiative forcing that enhanced atmospheric stability associated with the aerosol direct and first indirect effects. The significant reduction in summer precipitation in East Asia is also consistent with the weakening of the East Asian summer monsoon, resulting from the decreasing thermodynamic contrast between the Asian landmass and the surrounding oceans induced by the aerosol??s radiative effects. The increase in aerosols reduces the surface net shortwave radiative flux over the East Asia landmass, which leads to the reduction of the land surface temperature. With minimal changes in the sea surface temperature, hence, the weakening of the East Asian summer monsoon further enhances the reduction of summer precipitation over East Asia.     

欧洲东部土壤湿度对东北亚初夏气温异常转折的影响及其可能物理过程

采用1979—2020年观测和再分析资料,研究了年际时间尺度上初夏(5—6月)东北亚气温异常月际转折的基本特征,以及欧洲东部土壤湿度异常对其的影响及可能物理过程。结果表明,年际时间尺度上东北亚初夏气温异常月际演变的主导模态为转折模态,即5月偏暖(冷)则6月偏冷(暖);转折模态的形成直接源于东北亚地区环流异常的转折。进一步分析发现,5月欧洲东部土壤湿度偏低往往导致东北亚5月偏暖而6月偏冷,可能的物理过程如下:5月土壤湿度偏低导致局地土壤温度和对流层低层增温,进而造成地中海地区(欧洲北部)对流层低层经向温度梯度和大气斜压性减弱(增强),相应地高频瞬变波活动减弱(增强),并通过瞬变涡度强迫有利于欧洲中东部形成异常高压和Rossby波波源;相关的Rossby波沿极锋急流东传,导致东北亚为准正压的异常高压,地表升温。土壤湿度异常可持续到6月,但强度减弱;类似地,其可通过瞬变涡度强迫有利于异常高压和Rossby波波源的形成,但中心西移至欧洲西部;相关Rossby波活动导致东北亚为准正压的异常低压,地表降温。5月和6月欧洲东部土壤湿度异常相关的 Rossby波的活动特征(波源、活动中心和传播路径)存在明显差异,这与两个月欧亚北部大气平均态的差异密切相关。当5月欧洲东部土壤湿度偏高时,上述物理过程则大致相反。     

Processes shaping the spatial pattern and seasonality of the surface air temperature response to anthropogenic forcing

In the period 1960–2010, the land surface air temperature (SAT) warmed more rapidly over some regions relative to the global mean. Using a set of time-slice experiments, we highlight how different physical processes shape the regional pattern of SAT warming. The results indicate an essential role of anthropogenic forcing in regional SAT changes from the 1970s to 2000s, and show that both surface–atmosphere interactions and large-scale atmospheric circulation changes can shape regional responses to forcing. Single forcing experiments show that an increase in greenhouse gases can lead to regional changes in land surface warming in winter (DJF) due to snow-albedo feedbacks, and in summer (JJA) due to soil-moisture and cloud feedbacks. Changes in anthropogenic aerosol and precursor (AA) emissions induce large spatial variations in SAT, characterized by warming over western Europe, Eurasia, and Alaska. In western Europe, SAT warming is stronger in JJA than in DJF due to substantial increases in clear sky shortwave radiation over Europe, associated with decreases in local AA emissions since the 1980s. In Alaska, the amplified SAT warming in DJF is due to increased downward longwave radiation, which is related to increased water vapor and cloud cover. In this case, although the model was able to capture the regional pattern of SAT change, and the associated local processes, it did not simulate all processes and anomalies correctly. For the Alaskan warming, the model is seen to achieve the correct regional response in the context of a wider North Pacific anomaly that is not consistent with observations. This demonstrates the importance of model evaluation that goes beyond the target variable in detection and attribution studies.