Data from July 2006 to June 2008 observed at SACOL （Semi-Arid Climate and Environment Observatory of Lanzhou University, 35.946°N, 104.137°E, elev. 1961 m）, a semi-arid site in Northwest China, are used to...Data from July 2006 to June 2008 observed at SACOL （Semi-Arid Climate and Environment Observatory of Lanzhou University, 35.946°N, 104.137°E, elev. 1961 m）, a semi-arid site in Northwest China, are used to study seasonal variability of soil moisture, along with surface albedo and other soil thermal parameters, such as heat capacity, thermal conductivity and thermal diffusivity, and their relationships to soil moisture content. The results indicate that surface albedo decreases with increases in soil moisture content, showing a typical exponential relation between the surface albedo and the soil moisture. The heat capacity, the soil thermal diffusivity, and soil thermal conductivity show large variations between Julian day 90-212 and 450-578. The soil thermal conductivity is found to increase as a power function of soil moisture. Soil heat capacity and soil thermal diffusivity increase with increases in soil moisture. The SACOL observed soil moisture are also used to validate the AMSR-E/AQUA retrieved soil moisture and there is good agreement between them. The analysis of the relationship between satellite retrieved soil moisture and precipitation suggests that the variability of soil moisture depends on the variation of precipitation over the Loess Plateau.展开更多
The relationship of surface albedo with the solar altitude angle and soil moisture is analyzed based on two-year （January 2002 to December 2003） observational data from the AWS （Automatic Weather Station） at MS347...The relationship of surface albedo with the solar altitude angle and soil moisture is analyzed based on two-year （January 2002 to December 2003） observational data from the AWS （Automatic Weather Station） at MS3478 in the northern Tibetan Plateau during the experimental period of CEOP/CAMP-Tibet （Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau）. As a double-variable （solar altitude angle and soil moisture） function, surface albedo varies inconspicuously with any single factor. By using the method of approximately separating the double-variable function into two, one-factor functions （product and addition）, the relationship of albedo with these two factors presents much better. The product and additional empirical formulae of albedo are then preliminarily fitted based on long-term experimental data. By comparison with observed values, it is found that the parameterization formulae fitted by using observational data are mostly reliable and their correlation coefficients are both over 0.6. The empirical formulae of albedo though, for the northern Tibetan Plateau, need to be tested by much more representative observational data with the help of numerical models and the retrieval of remote sensing data. It is practical until it is changed into effective parameterization formulae representing a grid scale in models.展开更多
Using radiation data from the Automatic Weather Stations (AWSs) for thermal balance obser-vations, which were set up at Lhasa, Nagqu, Xigaze and Nyingchi by the Sino-Japanese Asian Monsoon Mechanism Co-operative Proje...Using radiation data from the Automatic Weather Stations (AWSs) for thermal balance obser-vations, which were set up at Lhasa, Nagqu, Xigaze and Nyingchi by the Sino-Japanese Asian Monsoon Mechanism Co-operative Project in 1993–1996, and 1985–1989 Earth Radiation Balance Experiment (ERBE) measurements of Langley Research Center/NASA of US, and 1961–1996 monthly mean data from 148 surface stations over the Qinghai-Xizang Plateau (QXP) and its neighborhood, study is performed on empirical calculation methods of surface albedo, surface total radiation, planetary albedo and outgoing longwave radiation with the climatic features of radiation balance at the surface and the atmospheric top examined. Evidences suggest that the empirical formulae for surface albedo, planetary albedo, surface to-tal radiation and outgoing longwave radiation from the atmospheric top are capable of describing their seasonal and interannual variations over the QXP. The surface albedo is marked by noticeable seasonal variation and yearly mean of 0.22 with the maximum of 0.29 in January and minimum of 0.17 in July and August; in winter the albedo has great horizontal difference, bigger in the moun-tains than in the river valleys, and small in summer. The planetary albedo shows a smaller range of its annual variation with the yearly mean of 0.37, the maximum (minimum) occurring in February and March (autumn). In winter its high-value regions are mainly at Gar (Shiquanhe) in the western QXP and from the southwestern Qinghai to the northeastern Tibet and the low-value area at the northern slope of the central Himalayas; in summer, however, the albedo distribution displays clear-ly a progressive decrease from southeast to northwest. As for the surface total radiation, its values and annual varying range are smaller in the east than in the southwest. Its high-value center is at the southern slope of the Himalayas in winter and makes a conspicuous westward migration in spr-ing, remaining there for a long time, and it begins to retreat eastward in autumn. Monthly mean values of the surface net radiation are all positive and larger in summer than in winter. The net ra-diation is significantly intensified under the combined effect of surface total radiation and surface albedo from spring to early summer, resulting in the strongest sector in the mid plateau with its center staying nearly motionless from March to September, and is reduced in autumn dominantly by surface effective radiation. The earth-atmosphere system loses heat outward from October to next February and gains in other months. On an average, the plateau gains heat of 15 W m-2 on an annual basis. Key words The Qinghai-Xizang Plateau - Albedo - Radiation balance - Climatic feature (1)This work was supported under the auspices of the National (G1998040800) and CAS’s Key Project for Basic Research on Tibetan Plateau (KZ951-A1-204; KZ95T-06).展开更多
Understanding the energy balance on the Tibetan Plateau is important for better prediction of global climate change. To characterize the energy balance on the Plateau, we examined the radiation balance and the respons...Understanding the energy balance on the Tibetan Plateau is important for better prediction of global climate change. To characterize the energy balance on the Plateau, we examined the radiation balance and the response of albedo to environmental factors above an alpine meadow and an alpine wetland surfaces in the eastern Tibetan Plateau, using 2014 data. Although our two sites belong to the same climatic background, and are close geographically, the annual incident solar radiation at the alpine meadow site(6,447 MJ/(m2·a)) was about 1.1 times that at the alpine wetland site(6,012 MJ/(m2·a)),due to differences in the cloudiness between our two sites. The alpine meadow and the alpine wetland emitted about 38%and 42%, respectively, of annual incident solar radiation back into atmosphere in the form of net longwave radiation; and they reflected about 22% and 18%, respectively, of the annual incident solar radiation back into atmosphere in the form of shortwave radiation. The annual net radiation was 2,648 and 2,544 MJ/(m2·a) for the alpine meadow site and the alpine wetland site, respectively, accounting for only about 40% of the annual incident solar radiation, significantly lower than the global mean. At 30-min scales, surface albedo exponentially decreases with the increase of the solar elevation angle; and it linearly decreases with the increase of soil-water content for our two sites. But those relationships are significantly influenced by cloudiness and are site-specific.展开更多
Snowfall and the subsequent evolution of the snowpack have a large effect on the surface energy balance and water cycle of the Tibetan Plateau(TP).The effects of snow cover can be represented by the WRF coupled with a...Snowfall and the subsequent evolution of the snowpack have a large effect on the surface energy balance and water cycle of the Tibetan Plateau(TP).The effects of snow cover can be represented by the WRF coupled with a land surface scheme.The widely used Noah scheme is computationally efficient,but its poor representation of albedo needs considerable improvement.In this study,an improved albedo scheme is developed using a satellite-retrieved albedo that takes snow depth and age into account.Numerical experiments were then conducted to simulate a severe snow event in March 2017.The performance of the coupled WRF/Noah model,which implemented the improved albedo scheme,is compared against the model’s performance using the default Noah albedo scheme and against the coupled WRF/CLM that applied CLM albedo scheme.When the improved albedo scheme is implemented,the albedo overestimation in the southeastern TP is reduced,reducing the RMSE of the air temperature by 0.7°C.The improved albedo scheme also attains the highest correlation between the satellite-derived and the model-estimated albedo,which provides for a realistic representation of both the snow water equivalent(SWE)spatial distribution in the heavy snowbelt(SWE>6 mm)and the maximum SWE in the eastern TP.The underestimated albedo in the coupled WRF/CLM leads to underestimating the regional maximum SWE and a consequent failure to estimate SWE in the heavy snowbelt accurately.Our study demonstrates the feasibility of improving the Noah albedo scheme and provides a theoretical reference for researchers aiming to improve albedo schemes further.展开更多
The snow cover in the Tibetan Plateau(TP)responds keenly to global climate and hydrological shifts,with snow albedo variation serving as a pivotal indicator of these changes.In this study,we explored snow albedo chang...The snow cover in the Tibetan Plateau(TP)responds keenly to global climate and hydrological shifts,with snow albedo variation serving as a pivotal indicator of these changes.In this study,we explored snow albedo changes over the period(2001-2022)in the TP combined with the high-resolution near-surface meteorological forcing datasets(2001-2022).The study utilized Ding’s method to separate precipitation patterns,and then employed path analysis to evaluate the vertical response of snow albedo to air temperature,rainfall,and snowfall across four periods.The findings are as follows:(1)Snow albedo in area above 4000 m ranged from 0.4 to 0.7,while below 4000 m,snow albedo was primarily below 0.4.Snow albedo was generally higher in the northern TP.(2)During the snow accumulation period(October to December),snow albedo showed a decreasing trend in most areas of the TP.Conversely,snow albedo exhibited overall increasing trends during the snow stable period(January to February),snowmelt period(March to May),and snowless period(June to September).Especially in the central TP,snow albedo showed significant decrease during the snow accumulation period,and it increased significantly in the other periods.(3)Air temperature,rainfall,and snowfall influenced directly and predominantly snow albedo changes in the TP.Especially,air temperature and snowfall were the primary driving factors in most areas.(4)During different periods,air temperature was the main factor driving changes in snow albedo below 5000 m,but snowfall had a stronger influence above 5000 m.Except during the snow accumulation period,the impact of rainfall on snow albedo decreased with increasing altitude.During the snowless period,rainfall affected snow albedo obviously,but snowfall remained the dominant factor in areas above 6500 m.These results provide new insights on climate-driven changes in the snow albedo over the TP.展开更多
Land surface albedo plays a key role in regulating surface energy budgets and thereby land-atmosphere interactions.Most land surface models employ a so-called soil color parameter to determine albedos for dry/saturate...Land surface albedo plays a key role in regulating surface energy budgets and thereby land-atmosphere interactions.Most land surface models employ a so-called soil color parameter to determine albedos for dry/saturated soils,yet it is poorly characterized in the Weather Research and Forecasting(WRF)model,leading to an underestimation of summertime surface albedo on the Tibetan Plateau(TP).This study introduces an optimized soil color map,which can effectively enhance the simulation of surface albedo and land surface temperature over a 10-year climate modeling period.This improvement reduces the TP's thermal effect,along with decreased net radiation,latent,and sensible heat during the summer,leading to an increase in geopotential height in the lower troposphere and a reduction in water vapor flux convergence.The resulting precipitation estimation shows a reduced wet bias(52%to 36%),as compared with IMERG and GSMaP products.Further evaluation against rain-gauge observations suggests that the incorporation of an optimized soil color map improves precipitation simulation at 66%of the stations,with mean wet bias mitigated from 1.02 to 0.82 mm d-1.The findings reveal that the underestimation of surface albedo is partially responsible for the wet bias in precipitation simulation.It also highlights the feasibility of improving climate modeling by optimizing land surface parameters,which is highly affordable through the joint use of land surface models and satellite remote sensing products.展开更多
A field observation on the albedo of the snowpack in Central Tibet was conducted in the Nam Co region in the winter of 2011. Snow properties, including grain size and density, were measured in the field, and surface-l...A field observation on the albedo of the snowpack in Central Tibet was conducted in the Nam Co region in the winter of 2011. Snow properties, including grain size and density, were measured in the field, and surface-layer snow samples （down to 5 cm） were collected. The average concentrations of black carbon and dust were 72 ppbm （close to that in the glaciers of Mt. Nyainqentanglha） and 120 ppmm, respectively. Inverse trends were found to exist between the albedo of the snowpack and light-absorbing aerosols （LAAs） as well as grain size growth. Modeling showed that black carbon, dust, and grain growth in the winter snowpack can reduce the broadband albedo by 11%, 28%, and 61%, respectively.展开更多
The combination of field experiments and satellite observations is the fundamental way to understand the characteristics of spatial-temporal variation in surface albedo over the Tibetan (Qinghai-Xizang) Plateau. Under...The combination of field experiments and satellite observations is the fundamental way to understand the characteristics of spatial-temporal variation in surface albedo over the Tibetan (Qinghai-Xizang) Plateau. Under the condition without snow cover, the relatively regular annual variation cycle of the surface albedo can be expressed by an empirical formula. The effect of snow cover on the surface albedo in winter can be expressed by introducing two variables of snow forcing and sensitivity parameter. The existing satellite retrieved results of surface albedo may provide the digital grid data for describing the geographical distribution. However, some satellite retrieved surface albedos available over the Tibetan Plateau are obviously too low in winter. Taking the satellite derived results in summer as the background field representative of geographical distribution and combining the empirical formula of annual cycle based on the surface observations, a dynamic model of surface albedo is developed for the need of modeling the climatic influence of the underlying surface forcing of the Tibetan Plateau.展开更多
An advanced three-level global atmospheric general circulation model has been used to study the summer precipitation anomaly in Northwest China.based on the synoptic fact and the statistical analysis of the precipitat...An advanced three-level global atmospheric general circulation model has been used to study the summer precipitation anomaly in Northwest China.based on the synoptic fact and the statistical analysis of the precipitation,the surface albedo in Northwest China,and the synoptic systems over the Tibetan(Qinghai-Xizang)Plateau.The results show that either the anticyclone intensified over the plateau or the surface alhedo enhanced in Northwest China results in summer precipitation reduction east of Northwest China.Especially.when both of them appear simultaneously,summer precipitation was obviously reduced and severe drought occurred in most areas of Northwest China.Moreover.the simulated difference of precipitation rate of Northwest China is similar to the actural precipitation distribution in Northwest China in 1995,which is the most severe drought year in Northwest China in the past fifty years.So the tendency in drought severity intensified,drought frequency accelerated,drought persistence period extended,and drought areas expanded in Northwest China in recent years is maybe a result of the influences of human activities(e.g.vegetation was reduced,and desertification worsened)on drought circulation pattens over the Tibetan Plateau.展开更多
The response of the warming magnitude over the Tibetan Plateau(TP;elevation≥3000 m)to global climate change is not spatially uniform.Rather,it enhances with elevation,referred to as elevation-dependent warming(EDW).T...The response of the warming magnitude over the Tibetan Plateau(TP;elevation≥3000 m)to global climate change is not spatially uniform.Rather,it enhances with elevation,referred to as elevation-dependent warming(EDW).The degree of EDW over the TP is season-dependent,with the largest amplitude of 0.21℃km^(−1)observed during boreal winter.Several factors have been proposed in previous studies as possible drivers of TP EDW,but the relative importance of these factors has been less studied.To quantitatively identify the major drivers of TP EDW in winter over recent decades(1979-2018),the authors applied the radiative kernels diagnostic method with several datasets.The results robustly suggest that,the surface albedo feedback associated with changes in snow cover plays the leading role in TP EDW.Observations show that the snow cover has reduced significantly over regions with high elevation during the winters of the past four decades,leading to reductions in outgoing shortwave radiation and thus EDW.展开更多
Satellite observations offer the potential of mapping and monitoring of the distribution and variation of surface albedo. Numerous studies have been conducted aiming at derivation of surface albedo from satellite sens...Satellite observations offer the potential of mapping and monitoring of the distribution and variation of surface albedo. Numerous studies have been conducted aiming at derivation of surface albedo from satellite sensor data. In regard to the transform of planetary albedo to surface albedo, it is the most important to establish the relationship between the clearsky and the surface albedo.展开更多
The Tibetan Plateau(TP)exerts a profound influence on global climate over million-year timescales due to its past uplift.However,whether the ongoing climate changes over the TP,particularly the persistent reduction in...The Tibetan Plateau(TP)exerts a profound influence on global climate over million-year timescales due to its past uplift.However,whether the ongoing climate changes over the TP,particularly the persistent reduction in its local albedo(referred to as“TP surface darkening”),can exert global impacts remains elusive.In this study,a state-of-the-art coupled land–atmosphere global climate model has been employed to scrutinize the impact of TP darkening on polar climate changes.Results indicate that the projected TP darkening has the potential to generate a stationary Rossby wave train,thereby modulating the atmospheric circulation in the high-latitudes of the Northern Hemisphere and instigating a dipole-like surface air temperature anomaly pattern around the Arctic region.An additional experiment suggests that the projected Arctic warming may in return warm the TP,thus forming a bi-directional linkage between these two climate systems.Given their association with vast ice reservoirs,the elucidation of this mechanism in our study is crucial in advancing our comprehension of Earth system climate projections.展开更多
Studies on optical properties of aerosols can reduce the uncertainty for modelling direct radiative forcing(DRF)and improve the accuracy for discussing aerosols effects on the Tibetan Plateau(TP)climate.This study inv...Studies on optical properties of aerosols can reduce the uncertainty for modelling direct radiative forcing(DRF)and improve the accuracy for discussing aerosols effects on the Tibetan Plateau(TP)climate.This study investigated the spatiotemporal variation of aerosol optical and microphysical properties over TP based on OMI and MERRA2,and assessed the influence of aerosol optical properties on DRF at NamCo station(30°46.44′N,90°59.31′E,4730 m)in the central TP from 2006 to 2017 based on a long measurement of AERONET and the modelling of SBDART model.The results show that aerosol optical depth(AOD)exhibits obvious seasonal variation over TP,with higher AOD500nm(>0.75)during spring and summer,and lower value(<0.25)in autumn and winter.The aerosol concentrations show a fluctuated rising from 1980 to 2000,significant increasing from 2000 to 2010 and slight declining trend after 2013.Based on sensitivity experiments,it is found that AOD and single scattering albedo(SSA)have more important impact on the DRF compared withαvalues and ASY.When AOD440nm increases by 60%,DRF at the TOA and ATM is increased by 57.2%and 60.2%,respectively.When SSA440nm increases by 20%,DRF at the TOA and ATM decreases by 121%and 96.7%,respectively.展开更多
Tibetan Plateau(TP)is known as the“Third Pole”of the Earth.Any changes in land surface processes on the TP can have an unneglectable impact on regional and global climate.With the warming and wetting climate,the lan...Tibetan Plateau(TP)is known as the“Third Pole”of the Earth.Any changes in land surface processes on the TP can have an unneglectable impact on regional and global climate.With the warming and wetting climate,the land surface of the TP saw a darkening trend featured by decreasing surface albedo over the past decades,primarily due to the melting of glaciers,snow,and greening vegetation.Recent studies have investigated the effects of the TP land surface darkening on the field of climate,but these assessments only address one aspect of the feedback loop.How do these darkening-induced climate changes affect the frozen ground and ecosystems on the TP?In this study,we investigated the impact of TP land surface darkening on regional frozen ground and ecosystems using the state-of-the-art land surface model ORCHIDEE-MICT.Our model results show that darkening-induced climate changes on the TP will lead to a reduction in the area of regional frozen ground by 1.1×10~4±0.019×10~4km~2,a deepening of the regional permafrost active layer by 0.06±0.0004 m,and a decrease in the maximum freezing depth of regional seasonal frozen ground by 0.06±0.0016 m compared to the scenario without TP land surface darkening.Furthermore,the darkening-induced climate change on the TP will result in an increase in the regional leaf area index and an enhancement in the regional gross primary productivity,ultimately leading to an increase in regional terrestrial carbon stock by0.81±0.001 PgC.This study addresses the remaining piece of the puzzle in the feedback loop of TP land surface darkening,and improves our understanding of interactions across multiple spheres on the TP.The exacerbated regional permafrost degradation and increasing regional terrestrial carbon stock induced by TP land surface darkening should be considered in the development of national ecological security barrier.展开更多
基金supported bythe National Natural Science Foundation of China un-der Grants Nos40725015 and 40633017the Na-tional Basic Research Program of China under Grant No2006CB400501
文摘Data from July 2006 to June 2008 observed at SACOL （Semi-Arid Climate and Environment Observatory of Lanzhou University, 35.946°N, 104.137°E, elev. 1961 m）, a semi-arid site in Northwest China, are used to study seasonal variability of soil moisture, along with surface albedo and other soil thermal parameters, such as heat capacity, thermal conductivity and thermal diffusivity, and their relationships to soil moisture content. The results indicate that surface albedo decreases with increases in soil moisture content, showing a typical exponential relation between the surface albedo and the soil moisture. The heat capacity, the soil thermal diffusivity, and soil thermal conductivity show large variations between Julian day 90-212 and 450-578. The soil thermal conductivity is found to increase as a power function of soil moisture. Soil heat capacity and soil thermal diffusivity increase with increases in soil moisture. The SACOL observed soil moisture are also used to validate the AMSR-E/AQUA retrieved soil moisture and there is good agreement between them. The analysis of the relationship between satellite retrieved soil moisture and precipitation suggests that the variability of soil moisture depends on the variation of precipitation over the Loess Plateau.
基金supported by the National Basic Research Pro-gram of China (Grant No. 2005CB422003)National Natural Science Foundation of China (Grant No. 40875005)+1 种基金the Program of Institute of Plateau Meteorology of China Meteorological Administration (BROP200803)the Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau (CEOP/CAMP-Tibet)
文摘The relationship of surface albedo with the solar altitude angle and soil moisture is analyzed based on two-year （January 2002 to December 2003） observational data from the AWS （Automatic Weather Station） at MS3478 in the northern Tibetan Plateau during the experimental period of CEOP/CAMP-Tibet （Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau）. As a double-variable （solar altitude angle and soil moisture） function, surface albedo varies inconspicuously with any single factor. By using the method of approximately separating the double-variable function into two, one-factor functions （product and addition）, the relationship of albedo with these two factors presents much better. The product and additional empirical formulae of albedo are then preliminarily fitted based on long-term experimental data. By comparison with observed values, it is found that the parameterization formulae fitted by using observational data are mostly reliable and their correlation coefficients are both over 0.6. The empirical formulae of albedo though, for the northern Tibetan Plateau, need to be tested by much more representative observational data with the help of numerical models and the retrieval of remote sensing data. It is practical until it is changed into effective parameterization formulae representing a grid scale in models.
文摘Using radiation data from the Automatic Weather Stations (AWSs) for thermal balance obser-vations, which were set up at Lhasa, Nagqu, Xigaze and Nyingchi by the Sino-Japanese Asian Monsoon Mechanism Co-operative Project in 1993–1996, and 1985–1989 Earth Radiation Balance Experiment (ERBE) measurements of Langley Research Center/NASA of US, and 1961–1996 monthly mean data from 148 surface stations over the Qinghai-Xizang Plateau (QXP) and its neighborhood, study is performed on empirical calculation methods of surface albedo, surface total radiation, planetary albedo and outgoing longwave radiation with the climatic features of radiation balance at the surface and the atmospheric top examined. Evidences suggest that the empirical formulae for surface albedo, planetary albedo, surface to-tal radiation and outgoing longwave radiation from the atmospheric top are capable of describing their seasonal and interannual variations over the QXP. The surface albedo is marked by noticeable seasonal variation and yearly mean of 0.22 with the maximum of 0.29 in January and minimum of 0.17 in July and August; in winter the albedo has great horizontal difference, bigger in the moun-tains than in the river valleys, and small in summer. The planetary albedo shows a smaller range of its annual variation with the yearly mean of 0.37, the maximum (minimum) occurring in February and March (autumn). In winter its high-value regions are mainly at Gar (Shiquanhe) in the western QXP and from the southwestern Qinghai to the northeastern Tibet and the low-value area at the northern slope of the central Himalayas; in summer, however, the albedo distribution displays clear-ly a progressive decrease from southeast to northwest. As for the surface total radiation, its values and annual varying range are smaller in the east than in the southwest. Its high-value center is at the southern slope of the Himalayas in winter and makes a conspicuous westward migration in spr-ing, remaining there for a long time, and it begins to retreat eastward in autumn. Monthly mean values of the surface net radiation are all positive and larger in summer than in winter. The net ra-diation is significantly intensified under the combined effect of surface total radiation and surface albedo from spring to early summer, resulting in the strongest sector in the mid plateau with its center staying nearly motionless from March to September, and is reduced in autumn dominantly by surface effective radiation. The earth-atmosphere system loses heat outward from October to next February and gains in other months. On an average, the plateau gains heat of 15 W m-2 on an annual basis. Key words The Qinghai-Xizang Plateau - Albedo - Radiation balance - Climatic feature (1)This work was supported under the auspices of the National (G1998040800) and CAS’s Key Project for Basic Research on Tibetan Plateau (KZ951-A1-204; KZ95T-06).
基金supported by the National Natural Science Foundation of China (Grant Nos. 91537106, 41405016, 41275016, 91537104, and 41605011)
文摘Understanding the energy balance on the Tibetan Plateau is important for better prediction of global climate change. To characterize the energy balance on the Plateau, we examined the radiation balance and the response of albedo to environmental factors above an alpine meadow and an alpine wetland surfaces in the eastern Tibetan Plateau, using 2014 data. Although our two sites belong to the same climatic background, and are close geographically, the annual incident solar radiation at the alpine meadow site(6,447 MJ/(m2·a)) was about 1.1 times that at the alpine wetland site(6,012 MJ/(m2·a)),due to differences in the cloudiness between our two sites. The alpine meadow and the alpine wetland emitted about 38%and 42%, respectively, of annual incident solar radiation back into atmosphere in the form of net longwave radiation; and they reflected about 22% and 18%, respectively, of the annual incident solar radiation back into atmosphere in the form of shortwave radiation. The annual net radiation was 2,648 and 2,544 MJ/(m2·a) for the alpine meadow site and the alpine wetland site, respectively, accounting for only about 40% of the annual incident solar radiation, significantly lower than the global mean. At 30-min scales, surface albedo exponentially decreases with the increase of the solar elevation angle; and it linearly decreases with the increase of soil-water content for our two sites. But those relationships are significantly influenced by cloudiness and are site-specific.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20060101)the Second Tibetan Plateau Scientific Expedition and Research program(STEP)(2019QZKK0103)+4 种基金the National Natural Science Foundation of China(Grant Nos.91837208,91637312,41830650,and 91737205)MOST High-Level Talent Grant No.G20190161018the Chinese Academy of Sciences President’s International Fellowship Initiative Grant No.2020VTA0001the Key Research Program of Frontier Sciences of Chinese Academy of Sciences(QYZDJ-SSW-DQC019)Key Research and Development Projects of the Ministry of Science and Technology(2018YFC1505701).
文摘Snowfall and the subsequent evolution of the snowpack have a large effect on the surface energy balance and water cycle of the Tibetan Plateau(TP).The effects of snow cover can be represented by the WRF coupled with a land surface scheme.The widely used Noah scheme is computationally efficient,but its poor representation of albedo needs considerable improvement.In this study,an improved albedo scheme is developed using a satellite-retrieved albedo that takes snow depth and age into account.Numerical experiments were then conducted to simulate a severe snow event in March 2017.The performance of the coupled WRF/Noah model,which implemented the improved albedo scheme,is compared against the model’s performance using the default Noah albedo scheme and against the coupled WRF/CLM that applied CLM albedo scheme.When the improved albedo scheme is implemented,the albedo overestimation in the southeastern TP is reduced,reducing the RMSE of the air temperature by 0.7°C.The improved albedo scheme also attains the highest correlation between the satellite-derived and the model-estimated albedo,which provides for a realistic representation of both the snow water equivalent(SWE)spatial distribution in the heavy snowbelt(SWE>6 mm)and the maximum SWE in the eastern TP.The underestimated albedo in the coupled WRF/CLM leads to underestimating the regional maximum SWE and a consequent failure to estimate SWE in the heavy snowbelt accurately.Our study demonstrates the feasibility of improving the Noah albedo scheme and provides a theoretical reference for researchers aiming to improve albedo schemes further.
基金supported by the National Natural Sciences Foundation of China(42261026,41971094,and 42161025)Gansu Science and Technology Research Project(22ZD6FA005)+1 种基金Higher Education Innovation Foundation of Education Department of Gansu Province(2022A 041)the open foundation of Xinjiang Key Laboratory of Water Cycle and Utilization in Arid Zone(XJYS0907-2023-01).
文摘The snow cover in the Tibetan Plateau(TP)responds keenly to global climate and hydrological shifts,with snow albedo variation serving as a pivotal indicator of these changes.In this study,we explored snow albedo changes over the period(2001-2022)in the TP combined with the high-resolution near-surface meteorological forcing datasets(2001-2022).The study utilized Ding’s method to separate precipitation patterns,and then employed path analysis to evaluate the vertical response of snow albedo to air temperature,rainfall,and snowfall across four periods.The findings are as follows:(1)Snow albedo in area above 4000 m ranged from 0.4 to 0.7,while below 4000 m,snow albedo was primarily below 0.4.Snow albedo was generally higher in the northern TP.(2)During the snow accumulation period(October to December),snow albedo showed a decreasing trend in most areas of the TP.Conversely,snow albedo exhibited overall increasing trends during the snow stable period(January to February),snowmelt period(March to May),and snowless period(June to September).Especially in the central TP,snow albedo showed significant decrease during the snow accumulation period,and it increased significantly in the other periods.(3)Air temperature,rainfall,and snowfall influenced directly and predominantly snow albedo changes in the TP.Especially,air temperature and snowfall were the primary driving factors in most areas.(4)During different periods,air temperature was the main factor driving changes in snow albedo below 5000 m,but snowfall had a stronger influence above 5000 m.Except during the snow accumulation period,the impact of rainfall on snow albedo decreased with increasing altitude.During the snowless period,rainfall affected snow albedo obviously,but snowfall remained the dominant factor in areas above 6500 m.These results provide new insights on climate-driven changes in the snow albedo over the TP.
基金supported by the Open Research Fund of TPESER(Grant No.TPESER202506)the National Key R&D Program of China(Grant No.2024YFC3013403)+5 种基金the National Natural Science Foundation of China(Grant Nos.42271491,42205155,and 42371085)the National Institute of Natural Hazards,Ministry of Emergency Management of China(Grant No.ZDJ2024-25)supported by the National Key Scientific and Technological Infrastructure Project“Earth System Numerical Simulation Facility”(Earth Lab)the CASEarth Cloud Platform(http://portal.casearth.cn)of the Computer Network Information CenterChinese Academy of Sciencesthe Supercomputing Center of Lanzhou University。
文摘Land surface albedo plays a key role in regulating surface energy budgets and thereby land-atmosphere interactions.Most land surface models employ a so-called soil color parameter to determine albedos for dry/saturated soils,yet it is poorly characterized in the Weather Research and Forecasting(WRF)model,leading to an underestimation of summertime surface albedo on the Tibetan Plateau(TP).This study introduces an optimized soil color map,which can effectively enhance the simulation of surface albedo and land surface temperature over a 10-year climate modeling period.This improvement reduces the TP's thermal effect,along with decreased net radiation,latent,and sensible heat during the summer,leading to an increase in geopotential height in the lower troposphere and a reduction in water vapor flux convergence.The resulting precipitation estimation shows a reduced wet bias(52%to 36%),as compared with IMERG and GSMaP products.Further evaluation against rain-gauge observations suggests that the incorporation of an optimized soil color map improves precipitation simulation at 66%of the stations,with mean wet bias mitigated from 1.02 to 0.82 mm d-1.The findings reveal that the underestimation of surface albedo is partially responsible for the wet bias in precipitation simulation.It also highlights the feasibility of improving climate modeling by optimizing land surface parameters,which is highly affordable through the joint use of land surface models and satellite remote sensing products.
基金supported by the National Natural Science Foundation of China (No.40901046)the National Natural Science Foundation of China (No.41121001)+3 种基金the Global Change Research Program of China (No.2010CB951401)the State Key Laboratory of Cryospheric Sciences (No.SKLCS-ZZ-2012-01-06)China Meteorological Administration (No.GYHY201106023)the Climate Change Science Foundation of CMA (2013–2014)
文摘A field observation on the albedo of the snowpack in Central Tibet was conducted in the Nam Co region in the winter of 2011. Snow properties, including grain size and density, were measured in the field, and surface-layer snow samples （down to 5 cm） were collected. The average concentrations of black carbon and dust were 72 ppbm （close to that in the glaciers of Mt. Nyainqentanglha） and 120 ppmm, respectively. Inverse trends were found to exist between the albedo of the snowpack and light-absorbing aerosols （LAAs） as well as grain size growth. Modeling showed that black carbon, dust, and grain growth in the winter snowpack can reduce the broadband albedo by 11%, 28%, and 61%, respectively.
基金This work was sponsored by the State ScienceTechnology Commission of China under GrantsKJ85-07 and PD-26
文摘The combination of field experiments and satellite observations is the fundamental way to understand the characteristics of spatial-temporal variation in surface albedo over the Tibetan (Qinghai-Xizang) Plateau. Under the condition without snow cover, the relatively regular annual variation cycle of the surface albedo can be expressed by an empirical formula. The effect of snow cover on the surface albedo in winter can be expressed by introducing two variables of snow forcing and sensitivity parameter. The existing satellite retrieved results of surface albedo may provide the digital grid data for describing the geographical distribution. However, some satellite retrieved surface albedos available over the Tibetan Plateau are obviously too low in winter. Taking the satellite derived results in summer as the background field representative of geographical distribution and combining the empirical formula of annual cycle based on the surface observations, a dynamic model of surface albedo is developed for the need of modeling the climatic influence of the underlying surface forcing of the Tibetan Plateau.
文摘An advanced three-level global atmospheric general circulation model has been used to study the summer precipitation anomaly in Northwest China.based on the synoptic fact and the statistical analysis of the precipitation,the surface albedo in Northwest China,and the synoptic systems over the Tibetan(Qinghai-Xizang)Plateau.The results show that either the anticyclone intensified over the plateau or the surface alhedo enhanced in Northwest China results in summer precipitation reduction east of Northwest China.Especially.when both of them appear simultaneously,summer precipitation was obviously reduced and severe drought occurred in most areas of Northwest China.Moreover.the simulated difference of precipitation rate of Northwest China is similar to the actural precipitation distribution in Northwest China in 1995,which is the most severe drought year in Northwest China in the past fifty years.So the tendency in drought severity intensified,drought frequency accelerated,drought persistence period extended,and drought areas expanded in Northwest China in recent years is maybe a result of the influences of human activities(e.g.vegetation was reduced,and desertification worsened)on drought circulation pattens over the Tibetan Plateau.
基金supported by the National Natural Science Foundation of China[grant number 4225502].
文摘The response of the warming magnitude over the Tibetan Plateau(TP;elevation≥3000 m)to global climate change is not spatially uniform.Rather,it enhances with elevation,referred to as elevation-dependent warming(EDW).The degree of EDW over the TP is season-dependent,with the largest amplitude of 0.21℃km^(−1)observed during boreal winter.Several factors have been proposed in previous studies as possible drivers of TP EDW,but the relative importance of these factors has been less studied.To quantitatively identify the major drivers of TP EDW in winter over recent decades(1979-2018),the authors applied the radiative kernels diagnostic method with several datasets.The results robustly suggest that,the surface albedo feedback associated with changes in snow cover plays the leading role in TP EDW.Observations show that the snow cover has reduced significantly over regions with high elevation during the winters of the past four decades,leading to reductions in outgoing shortwave radiation and thus EDW.
基金Project supported by the National Natural Science Foundation of China.
文摘Satellite observations offer the potential of mapping and monitoring of the distribution and variation of surface albedo. Numerous studies have been conducted aiming at derivation of surface albedo from satellite sensor data. In regard to the transform of planetary albedo to surface albedo, it is the most important to establish the relationship between the clearsky and the surface albedo.
基金This work was supported by the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0208)the National Natural Science Foundation of China(41988101)the Xplorer Prize.
文摘The Tibetan Plateau(TP)exerts a profound influence on global climate over million-year timescales due to its past uplift.However,whether the ongoing climate changes over the TP,particularly the persistent reduction in its local albedo(referred to as“TP surface darkening”),can exert global impacts remains elusive.In this study,a state-of-the-art coupled land–atmosphere global climate model has been employed to scrutinize the impact of TP darkening on polar climate changes.Results indicate that the projected TP darkening has the potential to generate a stationary Rossby wave train,thereby modulating the atmospheric circulation in the high-latitudes of the Northern Hemisphere and instigating a dipole-like surface air temperature anomaly pattern around the Arctic region.An additional experiment suggests that the projected Arctic warming may in return warm the TP,thus forming a bi-directional linkage between these two climate systems.Given their association with vast ice reservoirs,the elucidation of this mechanism in our study is crucial in advancing our comprehension of Earth system climate projections.
基金funded by the National Natural Science Foundation of China(Grant Nos.42175106,91837103)China Postdoctoral Science Foundation(Grant No.2020M681156).
文摘Studies on optical properties of aerosols can reduce the uncertainty for modelling direct radiative forcing(DRF)and improve the accuracy for discussing aerosols effects on the Tibetan Plateau(TP)climate.This study investigated the spatiotemporal variation of aerosol optical and microphysical properties over TP based on OMI and MERRA2,and assessed the influence of aerosol optical properties on DRF at NamCo station(30°46.44′N,90°59.31′E,4730 m)in the central TP from 2006 to 2017 based on a long measurement of AERONET and the modelling of SBDART model.The results show that aerosol optical depth(AOD)exhibits obvious seasonal variation over TP,with higher AOD500nm(>0.75)during spring and summer,and lower value(<0.25)in autumn and winter.The aerosol concentrations show a fluctuated rising from 1980 to 2000,significant increasing from 2000 to 2010 and slight declining trend after 2013.Based on sensitivity experiments,it is found that AOD and single scattering albedo(SSA)have more important impact on the DRF compared withαvalues and ASY.When AOD440nm increases by 60%,DRF at the TOA and ATM is increased by 57.2%and 60.2%,respectively.When SSA440nm increases by 20%,DRF at the TOA and ATM decreases by 121%and 96.7%,respectively.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(Grant No.2019QZKK0208)the National Natural Science Foundation of China(Grant Nos.41988101,42425106)。
文摘Tibetan Plateau(TP)is known as the“Third Pole”of the Earth.Any changes in land surface processes on the TP can have an unneglectable impact on regional and global climate.With the warming and wetting climate,the land surface of the TP saw a darkening trend featured by decreasing surface albedo over the past decades,primarily due to the melting of glaciers,snow,and greening vegetation.Recent studies have investigated the effects of the TP land surface darkening on the field of climate,but these assessments only address one aspect of the feedback loop.How do these darkening-induced climate changes affect the frozen ground and ecosystems on the TP?In this study,we investigated the impact of TP land surface darkening on regional frozen ground and ecosystems using the state-of-the-art land surface model ORCHIDEE-MICT.Our model results show that darkening-induced climate changes on the TP will lead to a reduction in the area of regional frozen ground by 1.1×10~4±0.019×10~4km~2,a deepening of the regional permafrost active layer by 0.06±0.0004 m,and a decrease in the maximum freezing depth of regional seasonal frozen ground by 0.06±0.0016 m compared to the scenario without TP land surface darkening.Furthermore,the darkening-induced climate change on the TP will result in an increase in the regional leaf area index and an enhancement in the regional gross primary productivity,ultimately leading to an increase in regional terrestrial carbon stock by0.81±0.001 PgC.This study addresses the remaining piece of the puzzle in the feedback loop of TP land surface darkening,and improves our understanding of interactions across multiple spheres on the TP.The exacerbated regional permafrost degradation and increasing regional terrestrial carbon stock induced by TP land surface darkening should be considered in the development of national ecological security barrier.
