Using observed daily precipitation data to classify five levels of rainy days by strength in South China （SC）,with an emphasis on the Pearl River Delta （PRD） region,the spatiotemporal variation of different grades...Using observed daily precipitation data to classify five levels of rainy days by strength in South China （SC）,with an emphasis on the Pearl River Delta （PRD） region,the spatiotemporal variation of different grades of precipitation during the period 1960-2010 was analyzed and the possible link with anthropogenic aerosols examined.Statistical analysis showed that drizzle and small precipitation has significantly decreased,whereas medium to heavy precipitation has increased slightly over the past 50 years （although not statistically significant）.Further data analysis suggested that the decline in drizzle and small precipitation probably has a strong link to increased concentrations of anthropogenic aerosols produced by large-scale human activities related to the rapid socioeconomic development of the PRD region.These aerosols may also have led to the obvious decreasing trend in horizontal visibility and sunshine duration in SC,which is statistically significant according to the t-test.展开更多
利用气象与化学模块在线耦合的模式WRF-Chem V3.5(Weather Research and Forecasting Model coupled to Chemistry Version 3.5)对1323号台风Fitow进行了模拟,设计无人为排放源、含人为排放源和人为排放源增加的三组模拟试验,对比分析...利用气象与化学模块在线耦合的模式WRF-Chem V3.5(Weather Research and Forecasting Model coupled to Chemistry Version 3.5)对1323号台风Fitow进行了模拟,设计无人为排放源、含人为排放源和人为排放源增加的三组模拟试验,对比分析了人为气溶胶对台风的影响。结果表明:人为气溶胶对台风移动路径影响较小。人为气溶胶增加,台风强度减弱,台风主体总累积降水量减少,靠近陆地阶段台风主体降水率减少。气溶胶的增多可提供更多的凝结核,台风外围云水增加,更多的云水可上升至冻结层以上形成过冷水,促进冰相粒子的形成,释放的潜热增加,使外围对流增强,降水增加。台风外围对流的发展,使低层入流的暖湿空气更多的在外围上升,向台风中心的入流减弱,眼墙的发展减弱,降水减少,台风强度减弱。台风外围的对流发展弱于眼墙的对流,降水仍以眼墙区为主,使累积降水量和降水率整体上表现为减少。展开更多
The eff ect of anthropogenic aerosols on the spring persistent rain （SPR） over eastern China is investigated by using a high-resolution Community Atmosphere Model version 5.1 （CAM5.1）. The results show that the SP...The eff ect of anthropogenic aerosols on the spring persistent rain （SPR） over eastern China is investigated by using a high-resolution Community Atmosphere Model version 5.1 （CAM5.1）. The results show that the SPR starts later due to anthropogenic aerosols, with a shortened duration and reduced rainfall amount. A reduction in air temperature over the low latitudes in East Asia is linked to anthropogenic aerosols;so is a weakened southwesterly on the north side of the subtropical high. Meanwhile, air temperature increases signifi cantly over the high latitudes. This north-south asymmetrical thermal eff ect acts to reduce the meridional temperature gradient, weakening the upper-level westerly jet over East Asia and the vertical motion over southeastern China. As a result, the SPR is reduced and has a much shorter duration. The indirect eff ect of anthropogenic aerosols also plays an important role in changing the SPR. Cloud droplet number concentration increases due to anthropogenic aerosols acting as cloud condensation nuclei, leading to a reduction in cloud eff ective radius over eastern China and a reduced precipitation effi ciency there.展开更多
In this study, a combination of satellite observations and reanalysis datasets is used to analyze the spatiotemporal distribution, classification and source of pollutants over the eastern slope of the Tibetan Plateau(...In this study, a combination of satellite observations and reanalysis datasets is used to analyze the spatiotemporal distribution, classification and source of pollutants over the eastern slope of the Tibetan Plateau(ESTP). The aerosol optical depth(AOD) over the ESTP is extremely large and even larger than some important industrialized regions and deserts. The main aerosol component over the ESTP is sulfate, followed by carbonaceous and dust aerosols. Local emissions related to human activity directly contribute to the accumulation of sulfate and carbonaceous aerosols over the Sichuan Basin. In addition, in spring, abundant carbonaceous aerosols emitted from forest, grassland and savanna fires in Southeast Asia can be transported by the prevailing southwesterly wind to southern China and the ESTP. The dust AOD over the ESTP peaks in spring because of the transport from the Taklimakan and Gobi deserts. Additionally, the high aerosol loading over the ESTP is also directly related to the meteorological background. Due to the special topography, the terrain-driven circulation can trap aerosols in the Sichuan Basin and these aerosols can climb along the ESTP due to the perennial updraft. The aerosol loading is lowest in summer because of effective wet deposition induced by the strong precipitation and better dispersion conditions due to the larger vertical temperature gradients and ascending air movement enhanced by the plateau heat pump effect. In contrast,the aerosol loading is greatest in winter. Abundant anthropogenic aerosols over the ESTP may generate some climatic and environmental risks and consequently greatly influence the downstream regions.展开更多
There have been extensive studies on poleward expansion of the Hadley cells and the associated poleward shift of subtropical dry zones in the past decade.In the present study,we study the trends in the width and stren...There have been extensive studies on poleward expansion of the Hadley cells and the associated poleward shift of subtropical dry zones in the past decade.In the present study,we study the trends in the width and strength of the Hadley cells,using currently available simulation results of the Coupled Model Intercomparison Project Phase-6(CMIP6),and compare the trends with that in CMIP5 simulations.Our results show that the total annual-mean trend in the width of the Hadley cells is 0.13°±0.02°per decade over 1970–2014 in CMIP6 historical All-forcing simulations.It is almost the same as that in CMIP5.The trend in the strength of the Northern-Hemisphere(NH)cell shows much greater weakening in CMIP6 than in CMIP5,while the strength trend in the Southern-Hemisphere(SH)cell shows slight strengthening.Single-forcing simulations demonstrate that increasing greenhouse gases cause widening and weakening of both the NH and SH Hadley cells,while anthropogenic aerosols and stratospheric ozone changes cause weak strengthening trends in the SH cell.CMIP6 projection simulation results show that both the widening and weakening trends increase with radiative forcing.展开更多
Influences of the mixing treatments of anthropogenic aerosols on their effective radiative forcing （ERF） and global aridity are evaluated by using the BCC_AGCM2.0_CUACE/Aero, an aerosol-climate online coupled model....Influences of the mixing treatments of anthropogenic aerosols on their effective radiative forcing （ERF） and global aridity are evaluated by using the BCC_AGCM2.0_CUACE/Aero, an aerosol-climate online coupled model. Simula-tions show that the negative ERF due to external mixing （EM, a scheme in which all aerosol particles are treated as independent spheres formed by single substance） aerosols is largely reduced by the partial internal mixing （PIM, a scheme in which some of the aerosol particles are formed by one absorptive and one scattering substance） method. Compared to EM, PIM aerosols have much stronger absorptive ability and generally weaker hygroscopicity, which would lead to changes in radiative forcing, hence to climate. For the global mean values, the ERFs due to anthropo-genie aerosols since the pre-industrial are -1.02 and -1.68 W m^-2 for PIM and EM schemes, respectively. The vari-ables related to aridity such as global mean temperature, net radiation flux at the surface, and the potential evapora-tion capacity are all decreased by 2.18/1.61 K, 5.06/3.90 W m^-2, and 0.21/0.14 mm day^-1 since 1850 for EM and PIM schemes, respectively. According to the changes in aridity index, the anthropogenic aerosols have caused general hu-midification over central Asia, South America, Africa, and Australia, but great aridification over eastern China and the Tibetan Plateau since the pre-industrial in both mixing schemes. However, the aridification is considerably allevi-ated in China, but intensified in the Arabian Peninsula and East Africa in the PIM scheme.展开更多
The WRF model with chemistry （WRF-Chem） was employed to simulate the impacts of anthropogenic aerosols on summer precipitation over the Beijing-Tianjin-Hebei urban agglomeration in China. With the aid of a high-reso...The WRF model with chemistry （WRF-Chem） was employed to simulate the impacts of anthropogenic aerosols on summer precipitation over the Beijing-Tianjin-Hebei urban agglomeration in China. With the aid of a high-resolution gridded inventory of anthropogenic emissions of trace gases and aerosols, we conducted relatively long-term regional simulations, considering direct, semi-direct and indirect effects of the aerosols. Comparing the results of sensitivity experiments with and without emissions, it was found that anthropogenic aerosols tended to enhance summer precipitation over the metropolitan areas. Domain-averaged rainfall was increased throughout the day, except for the time around noon. Aerosols shifted the precipitation probability distribution from light or moderate to extreme rain. Further analysis showed that the anthropogenic aerosol radiative forcing had a cooling effect at the land surface, but a warming effect in the atmosphere. However, enhanced convective strength and updrafts accompanied by water vapor increases and cyclone-like wind shear anomalies were found in the urban areas. These responses may originate from cloud microphysical effects of aerosols on convection, which were identified as the primary cause for the summer rainfall enhancement.展开更多
A coupled regional climate and aerosol-chemistry model, RIEMS 2.0 （Regional Integrated Environmental Model System for Asia）, in which anthropogenic sulfate, black carbon, and organic carbon were assumed to be extern...A coupled regional climate and aerosol-chemistry model, RIEMS 2.0 （Regional Integrated Environmental Model System for Asia）, in which anthropogenic sulfate, black carbon, and organic carbon were assumed to be externally mixed （EM）, internally mixed （IM） or partially internally mixed （IEM）, was used to simulate the impacts of these anthropogenic aerosols on East Asian climate for the entire year of 2006. The distributions of aerosol mass concentration, radiative forcing and hence the surface air temperature and precipitation variations under three mixing assumptions of aerosols were analyzed. The results indicated that the mass concentration of sulfate was sensitive to mixing assumptions, but carbonaceous aerosols were much less sensitive to the mixing types. Modeled results were compared with observations in a variety of sites in East Asia. It was found that the simulated concentrations of sulfate and carbonaceous aerosols were in accord with the observations in terms of magnitude. The simulated aerosol concentrations in IM case were closest to observation results. The regional average column burdens of sulfate, black carbon, and organic carbon, if internally mixed, were 11.49, 0.47, and 2.17 mg m 2 , respectively. The radiative forcing of anthropogenic aerosols at the top of the atmosphere increased from –1.27 （EM） to –1.97 W m 2 （IM） while the normalized radiative forcing （NRF） decreased from –0.145 （EM） to –0.139 W mg 1 （IM）. The radiative forcing and NRF were –1.82 W m 2 and –0.141 W mg 1 for IEM, respectively. The surface air temperature changes over the domain due to the anthropogenic sulfate and carbonaceous aerosols were –0.067, –0.078, and –0.072 K, with maxima of –0.47, –0.50, and –0.49 K, for EM, IM, and IEM, respectively. Meanwhile, the annual precipitation variations were –8.0 （EM）, –20.6 （IM）, and –21.9 mm （IEM）, with maxima of 148, 122, and 102 mm, respectively, indicating that the climate effects were stronger if the sul展开更多
Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth （AOD） and its accompanying shortwave radiative forcing （RF） are usually simulated by nu- merical...Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth （AOD） and its accompanying shortwave radiative forcing （RF） are usually simulated by nu- merical models. Recently, with the development of space-borne instruments and sophisticated retrieval algorithms, it has become possible to estimate aerosol radiative forcing based on satellite observations. In this study, we have estimated shortwave direct radiative forcing due to anthropogenic aerosols over oceans in all-sky conditions by combining clouds and the Single Scanner Footprint data of the Clouds and Earth’s Radiant Energy System （CERES/SSF） experiment, which provide measurements of upward shortwave fluxes at the top of atmosphere, with Moderate Resolution Imaging Spectroradiometer （MODIS） aerosol and cloud products. We found that globally averaged aerosol radiative forcing over oceans in the clear-sky conditions and all-sky conditions were -1.03±0.48 W m-2 and -0.34 ±0.16 W m-2, respectively. Direct radiative forcing by anthropogenic aerosols shows large regional and seasonal variations. In some regions and in particular seasons, the magnitude of direct forcing by anthropogenic aerosols can be comparable to the forcing of greenhouse gases. However, it shows that aerosols caused the cooling effect, rather than warming effect from global scale, which is different from greenhouse gases.展开更多
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-1990s. Observations indic...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-1990s. Observations indicate an abrupt increase in summer mean surface air temperature （SAT） over Northeast Asia since the mid-1990s. Accompanying this abrupt surface wanning, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature （Tmax）, daily minimum temperature （Train）, 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-1990s 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展开更多
为减少不同气候模式评估气溶胶气候效应的差异,第六次耦合模式比较计划(Coupled Model Intercomparison Project Phase 6,CMIP6)直接给定了人为气溶胶强迫数据。因此,有必要基于此强迫数据重新评估气溶胶气候效应。本研究首先将CMIP6给...为减少不同气候模式评估气溶胶气候效应的差异,第六次耦合模式比较计划(Coupled Model Intercomparison Project Phase 6,CMIP6)直接给定了人为气溶胶强迫数据。因此,有必要基于此强迫数据重新评估气溶胶气候效应。本研究首先将CMIP6给出的描述人为气溶胶强迫的模块引入南京信息工程大学(Nanjing University of Information Science and Technology,NUIST)的地球系统模式(The NUIST Earth System Model,NESM)。之后,利用NESM模式评估地球辐射收支平衡对此人为气溶胶强迫的响应,并分析模式模拟结果的不确定性。评估给出的人为气溶胶有效辐射强迫为-0.45(±0.28)W·m^-2。其中,气溶胶直接辐射效应为-0.34(±0.01)W·m^-2,与第二次气溶胶比较计划(The second phase of Aerosol Comparisons between Observations and Models,AeroComⅡ)的评估结果基本一致;气溶胶对云辐射强迫的影响(包括半直接效应和间接效应)为-0.10(±0.30)W·m^-2,明显受到模式内部变率的干扰,具有较大的不确定性。展开更多
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-EW-QN208)the National Basic Research Program of China (Grant No. 2010CB428502)+3 种基金the open fund of the State Key Laboratory of Remote Sensing Science (Grant No. OFSLRSS201113)the CAS Strategic Priority Research Program (Grant No. XDA05110103)the R&D Special Fund for Public Welfare Industry (meteorology) by the Ministry of Financethe Ministry of Science and Technology (Grant No. GYHY20100601404)
文摘Using observed daily precipitation data to classify five levels of rainy days by strength in South China （SC）,with an emphasis on the Pearl River Delta （PRD） region,the spatiotemporal variation of different grades of precipitation during the period 1960-2010 was analyzed and the possible link with anthropogenic aerosols examined.Statistical analysis showed that drizzle and small precipitation has significantly decreased,whereas medium to heavy precipitation has increased slightly over the past 50 years （although not statistically significant）.Further data analysis suggested that the decline in drizzle and small precipitation probably has a strong link to increased concentrations of anthropogenic aerosols produced by large-scale human activities related to the rapid socioeconomic development of the PRD region.These aerosols may also have led to the obvious decreasing trend in horizontal visibility and sunshine duration in SC,which is statistically significant according to the t-test.
文摘利用气象与化学模块在线耦合的模式WRF-Chem V3.5(Weather Research and Forecasting Model coupled to Chemistry Version 3.5)对1323号台风Fitow进行了模拟,设计无人为排放源、含人为排放源和人为排放源增加的三组模拟试验,对比分析了人为气溶胶对台风的影响。结果表明:人为气溶胶对台风移动路径影响较小。人为气溶胶增加,台风强度减弱,台风主体总累积降水量减少,靠近陆地阶段台风主体降水率减少。气溶胶的增多可提供更多的凝结核,台风外围云水增加,更多的云水可上升至冻结层以上形成过冷水,促进冰相粒子的形成,释放的潜热增加,使外围对流增强,降水增加。台风外围对流的发展,使低层入流的暖湿空气更多的在外围上升,向台风中心的入流减弱,眼墙的发展减弱,降水减少,台风强度减弱。台风外围的对流发展弱于眼墙的对流,降水仍以眼墙区为主,使累积降水量和降水率整体上表现为减少。
基金Supported by the National Basic Research and Development(973)Program of China(2010CB428505)National Natural Science Foundation of China(41275094)+1 种基金Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)Jiangsu Provincial Qinglan Project
文摘The eff ect of anthropogenic aerosols on the spring persistent rain （SPR） over eastern China is investigated by using a high-resolution Community Atmosphere Model version 5.1 （CAM5.1）. The results show that the SPR starts later due to anthropogenic aerosols, with a shortened duration and reduced rainfall amount. A reduction in air temperature over the low latitudes in East Asia is linked to anthropogenic aerosols;so is a weakened southwesterly on the north side of the subtropical high. Meanwhile, air temperature increases signifi cantly over the high latitudes. This north-south asymmetrical thermal eff ect acts to reduce the meridional temperature gradient, weakening the upper-level westerly jet over East Asia and the vertical motion over southeastern China. As a result, the SPR is reduced and has a much shorter duration. The indirect eff ect of anthropogenic aerosols also plays an important role in changing the SPR. Cloud droplet number concentration increases due to anthropogenic aerosols acting as cloud condensation nuclei, leading to a reduction in cloud eff ective radius over eastern China and a reduced precipitation effi ciency there.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91737101 and 91744311)supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA2006010301)
文摘In this study, a combination of satellite observations and reanalysis datasets is used to analyze the spatiotemporal distribution, classification and source of pollutants over the eastern slope of the Tibetan Plateau(ESTP). The aerosol optical depth(AOD) over the ESTP is extremely large and even larger than some important industrialized regions and deserts. The main aerosol component over the ESTP is sulfate, followed by carbonaceous and dust aerosols. Local emissions related to human activity directly contribute to the accumulation of sulfate and carbonaceous aerosols over the Sichuan Basin. In addition, in spring, abundant carbonaceous aerosols emitted from forest, grassland and savanna fires in Southeast Asia can be transported by the prevailing southwesterly wind to southern China and the ESTP. The dust AOD over the ESTP peaks in spring because of the transport from the Taklimakan and Gobi deserts. Additionally, the high aerosol loading over the ESTP is also directly related to the meteorological background. Due to the special topography, the terrain-driven circulation can trap aerosols in the Sichuan Basin and these aerosols can climb along the ESTP due to the perennial updraft. The aerosol loading is lowest in summer because of effective wet deposition induced by the strong precipitation and better dispersion conditions due to the larger vertical temperature gradients and ascending air movement enhanced by the plateau heat pump effect. In contrast,the aerosol loading is greatest in winter. Abundant anthropogenic aerosols over the ESTP may generate some climatic and environmental risks and consequently greatly influence the downstream regions.
基金supported by the National Natural Science Foundation of China(41530423,41761144072)supported by the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0604)。
文摘There have been extensive studies on poleward expansion of the Hadley cells and the associated poleward shift of subtropical dry zones in the past decade.In the present study,we study the trends in the width and strength of the Hadley cells,using currently available simulation results of the Coupled Model Intercomparison Project Phase-6(CMIP6),and compare the trends with that in CMIP5 simulations.Our results show that the total annual-mean trend in the width of the Hadley cells is 0.13°±0.02°per decade over 1970–2014 in CMIP6 historical All-forcing simulations.It is almost the same as that in CMIP5.The trend in the strength of the Northern-Hemisphere(NH)cell shows much greater weakening in CMIP6 than in CMIP5,while the strength trend in the Southern-Hemisphere(SH)cell shows slight strengthening.Single-forcing simulations demonstrate that increasing greenhouse gases cause widening and weakening of both the NH and SH Hadley cells,while anthropogenic aerosols and stratospheric ozone changes cause weak strengthening trends in the SH cell.CMIP6 projection simulation results show that both the widening and weakening trends increase with radiative forcing.
基金Supported by the(Key)National Natural Science Foundation of China(91644211 and 41575002)National Key Research and Development Program of China(2017YFA0603502)
文摘Influences of the mixing treatments of anthropogenic aerosols on their effective radiative forcing （ERF） and global aridity are evaluated by using the BCC_AGCM2.0_CUACE/Aero, an aerosol-climate online coupled model. Simula-tions show that the negative ERF due to external mixing （EM, a scheme in which all aerosol particles are treated as independent spheres formed by single substance） aerosols is largely reduced by the partial internal mixing （PIM, a scheme in which some of the aerosol particles are formed by one absorptive and one scattering substance） method. Compared to EM, PIM aerosols have much stronger absorptive ability and generally weaker hygroscopicity, which would lead to changes in radiative forcing, hence to climate. For the global mean values, the ERFs due to anthropo-genie aerosols since the pre-industrial are -1.02 and -1.68 W m^-2 for PIM and EM schemes, respectively. The vari-ables related to aridity such as global mean temperature, net radiation flux at the surface, and the potential evapora-tion capacity are all decreased by 2.18/1.61 K, 5.06/3.90 W m^-2, and 0.21/0.14 mm day^-1 since 1850 for EM and PIM schemes, respectively. According to the changes in aridity index, the anthropogenic aerosols have caused general hu-midification over central Asia, South America, Africa, and Australia, but great aridification over eastern China and the Tibetan Plateau since the pre-industrial in both mixing schemes. However, the aridification is considerably allevi-ated in China, but intensified in the Arabian Peninsula and East Africa in the PIM scheme.
基金supported by the Strategic Priority Research Program-Climate Change:Carbon Budget and Relevant Issuesof the Chinese Academy of Sciences(Grant No.XDA05090207)the National Natural Science Foundation of China(Grant Nos.41275108 and 41105051)
文摘The WRF model with chemistry （WRF-Chem） was employed to simulate the impacts of anthropogenic aerosols on summer precipitation over the Beijing-Tianjin-Hebei urban agglomeration in China. With the aid of a high-resolution gridded inventory of anthropogenic emissions of trace gases and aerosols, we conducted relatively long-term regional simulations, considering direct, semi-direct and indirect effects of the aerosols. Comparing the results of sensitivity experiments with and without emissions, it was found that anthropogenic aerosols tended to enhance summer precipitation over the metropolitan areas. Domain-averaged rainfall was increased throughout the day, except for the time around noon. Aerosols shifted the precipitation probability distribution from light or moderate to extreme rain. Further analysis showed that the anthropogenic aerosol radiative forcing had a cooling effect at the land surface, but a warming effect in the atmosphere. However, enhanced convective strength and updrafts accompanied by water vapor increases and cyclone-like wind shear anomalies were found in the urban areas. These responses may originate from cloud microphysical effects of aerosols on convection, which were identified as the primary cause for the summer rainfall enhancement.
基金Supported by the National Key Basic Research and Development (973) Program of China(2006CB400506 and 2010CB428501)National Natural Science Foundation of China(40775014)
文摘A coupled regional climate and aerosol-chemistry model, RIEMS 2.0 （Regional Integrated Environmental Model System for Asia）, in which anthropogenic sulfate, black carbon, and organic carbon were assumed to be externally mixed （EM）, internally mixed （IM） or partially internally mixed （IEM）, was used to simulate the impacts of these anthropogenic aerosols on East Asian climate for the entire year of 2006. The distributions of aerosol mass concentration, radiative forcing and hence the surface air temperature and precipitation variations under three mixing assumptions of aerosols were analyzed. The results indicated that the mass concentration of sulfate was sensitive to mixing assumptions, but carbonaceous aerosols were much less sensitive to the mixing types. Modeled results were compared with observations in a variety of sites in East Asia. It was found that the simulated concentrations of sulfate and carbonaceous aerosols were in accord with the observations in terms of magnitude. The simulated aerosol concentrations in IM case were closest to observation results. The regional average column burdens of sulfate, black carbon, and organic carbon, if internally mixed, were 11.49, 0.47, and 2.17 mg m 2 , respectively. The radiative forcing of anthropogenic aerosols at the top of the atmosphere increased from –1.27 （EM） to –1.97 W m 2 （IM） while the normalized radiative forcing （NRF） decreased from –0.145 （EM） to –0.139 W mg 1 （IM）. The radiative forcing and NRF were –1.82 W m 2 and –0.141 W mg 1 for IEM, respectively. The surface air temperature changes over the domain due to the anthropogenic sulfate and carbonaceous aerosols were –0.067, –0.078, and –0.072 K, with maxima of –0.47, –0.50, and –0.49 K, for EM, IM, and IEM, respectively. Meanwhile, the annual precipitation variations were –8.0 （EM）, –20.6 （IM）, and –21.9 mm （IEM）, with maxima of 148, 122, and 102 mm, respectively, indicating that the climate effects were stronger if the sul
基金supported by the Key Projects in the National Science & Technology Pillar Program in the Eleventh Five-year Plan Period (Grant No. 2008BAC40B01)the National Key Project of Basic Research of China (Grant No. 2010CB950802)Ministry of Science and Technology of China (Grant No. 2010DFA22770)
文摘Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth （AOD） and its accompanying shortwave radiative forcing （RF） are usually simulated by nu- merical models. Recently, with the development of space-borne instruments and sophisticated retrieval algorithms, it has become possible to estimate aerosol radiative forcing based on satellite observations. In this study, we have estimated shortwave direct radiative forcing due to anthropogenic aerosols over oceans in all-sky conditions by combining clouds and the Single Scanner Footprint data of the Clouds and Earth’s Radiant Energy System （CERES/SSF） experiment, which provide measurements of upward shortwave fluxes at the top of atmosphere, with Moderate Resolution Imaging Spectroradiometer （MODIS） aerosol and cloud products. We found that globally averaged aerosol radiative forcing over oceans in the clear-sky conditions and all-sky conditions were -1.03±0.48 W m-2 and -0.34 ±0.16 W m-2, respectively. Direct radiative forcing by anthropogenic aerosols shows large regional and seasonal variations. In some regions and in particular seasons, the magnitude of direct forcing by anthropogenic aerosols can be comparable to the forcing of greenhouse gases. However, it shows that aerosols caused the cooling effect, rather than warming effect from global scale, which is different from greenhouse gases.
基金supported by the UK– China Research & Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) of China, as part of the Newton Fundsupported by the UK National Centre for Atmospheric Science–Climate (NCAS– Climate) at the University of Reading
文摘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-1990s. Observations indicate an abrupt increase in summer mean surface air temperature （SAT） over Northeast Asia since the mid-1990s. Accompanying this abrupt surface wanning, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature （Tmax）, daily minimum temperature （Train）, 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-1990s 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
文摘为减少不同气候模式评估气溶胶气候效应的差异,第六次耦合模式比较计划(Coupled Model Intercomparison Project Phase 6,CMIP6)直接给定了人为气溶胶强迫数据。因此,有必要基于此强迫数据重新评估气溶胶气候效应。本研究首先将CMIP6给出的描述人为气溶胶强迫的模块引入南京信息工程大学(Nanjing University of Information Science and Technology,NUIST)的地球系统模式(The NUIST Earth System Model,NESM)。之后,利用NESM模式评估地球辐射收支平衡对此人为气溶胶强迫的响应,并分析模式模拟结果的不确定性。评估给出的人为气溶胶有效辐射强迫为-0.45(±0.28)W·m^-2。其中,气溶胶直接辐射效应为-0.34(±0.01)W·m^-2,与第二次气溶胶比较计划(The second phase of Aerosol Comparisons between Observations and Models,AeroComⅡ)的评估结果基本一致;气溶胶对云辐射强迫的影响(包括半直接效应和间接效应)为-0.10(±0.30)W·m^-2,明显受到模式内部变率的干扰,具有较大的不确定性。
