Based on the number of snow cover days （NSCDs） and homogenized surface air temperature data for the period 1951-2004, this study performs the quantitative analysis on the sensitivity of NSCDs to surface air temperat...Based on the number of snow cover days （NSCDs） and homogenized surface air temperature data for the period 1951-2004, this study performs the quantitative analysis on the sensitivity of NSCDs to surface air temperature over the Qinghai-Tibetan Plateau （QTP）. Results show that both the extreme sensitivity and sensitivity under current climate are higher in the edge than in the central area of the QTP. There exists a strong negative correlation between station＇s elevation and critical temperature, at which the sensitivity reaches extremum. The negative correlation between the elevation and the extreme sensitivity is not as strong as the former one. Currently, the climatological temperatures in quite a few stations do not reach the critical stage. The sensitivity at these stations will become greater under the current background of climate warming, which means NSCDs will be more sensitive to surface air temperature.展开更多
Using the Simple Biosphere Model （SiB2）, soil thermal properties （STP） were examined in a Tibetan prairie during the monsoon period to investigate ground surface temperature prediction. We improved the SiB2 model ...Using the Simple Biosphere Model （SiB2）, soil thermal properties （STP） were examined in a Tibetan prairie during the monsoon period to investigate ground surface temperature prediction. We improved the SiB2 model by incorporating a revised force-restore method （FRM） to take the vertical heterogeneity of soil thermal diffusivity （k） into account. The results indicate that （1） the revised FRM alleviates daytime overestimation and nighttime underestimation in modeled ground surface temperature （Tg）, and （2） its role in little rainfall events is significant because the vertical gradient of k increases with increasing surface evaporation. Since the original formula of thermal conductivity （A） in the SiB2 greatly underestimates soil thermal conductivity, we compared five Mgorithms of A involving soil moisture to investigate the cause of overestimation during the day and underestimation at night on the basis of the revised FRM. The results show that （1） the five algorithms significantly improve Tg prediction, especially in daytime, and （2） taking one of these five algorithms as an example, the simulated Tg values in the daytime are closer to the field measurements than those in the nighttime. The differences between modeled Tg and field measurements are mostly within the margin of error of -4-2 K during 3 August to 4 September 1998.展开更多
The increasing concentration of atmospheric CO_(2) since the Industrial Revolution has affected surface air temperature.However,the impact of the spatial distribution of atmospheric CO_(2) concentration on surface air...The increasing concentration of atmospheric CO_(2) since the Industrial Revolution has affected surface air temperature.However,the impact of the spatial distribution of atmospheric CO_(2) concentration on surface air temperature biases remains highly unclear.By incorporating the spatial distribution of satellite-derived atmospheric CO_(2) concentration in the Beijing Normal University Earth System Model,this study investigated the increase in surface air temperature since the Industrial Revolution in the Northern Hemisphere(NH) under historical conditions from 1976-2005.In comparison with the increase in surface temperature simulated using a uniform distribution of CO_(2),simulation with a nonuniform distribution of CO_(2)produced better agreement with the Climatic Research Unit(CRU) data in the NH under the historical condition relative to the baseline over the period 1901-30.Hemispheric June-July-August(JJA) surface air temperature increased by 1.28℃ ±0.29℃ in simulations with a uniform distribution of CO_(2),by 1.00℃±0.24℃ in simulations with a non-uniform distribution of CO_(2),and by 0.24℃ in the CRU data.The decrease in downward shortwave radiation in the non-uniform CO_(2) simulation was primarily attributable to reduced warming in Eurasia,combined with feedbacks resulting from increased leaf area index(LAI) and latent heat fluxes.These effects were more pronounced in the non-uniform CO_(2)simulation compared to the uniform CO_(2) simulation.Results indicate that consideration of the spatial distribution of CO_(2)concentration can reduce the overestimated increase in surface air temperature simulated by Earth system models.展开更多
The massive lockdown of human socioeconomic activities and vehicle movements due to the COVID-19 pandemic in 2020 has resulted in an unprecedented reduction in pollutant gases such as Nitrogen Dioxide(NO_(2))and Carbo...The massive lockdown of human socioeconomic activities and vehicle movements due to the COVID-19 pandemic in 2020 has resulted in an unprecedented reduction in pollutant gases such as Nitrogen Dioxide(NO_(2))and Carbon Monoxide(CO)as well as Land Surface Temperature(LST)in Amman as well as all countries around the globe.In this study,the spatial and temporal variability/stability of NO_(2),CO,and LST throughout the lockdown period over Amman city have been analyzed.The NO_(2) and CO column density values were acquired from Sentinel-5p while the LST data were obtained from MODIS satellite during the lockdown period from 20 March to 24 April in 2019,2020,and 2021.The statistical analysis showed an overall reduction in NO_(2) in 2020 by around 27% and 48% compared to 2019 and 2021,respectively.However,an increase of 7% in 2021 compared to 2019 was observed because almost all anthropogenic activities were allowed during the daytime.The temporal persistence showed almost constant NO2 values in 2020 over the study area throughout the lockdown period.In addition,a slight decrease in CO(around 1%)was recorded in 2020 and 2021 compared to the same period in 2019.Restrictions on human activities resulted in an evident drop in LST in 2020 by around 13%and 18% less than the 5-year average and 2021 respectively.The study concludes that due to the restrictions imposed on industrial activities and automobile movements in Amman city,an unprecedented reduction in NO_(2),CO,and LST was recorded.展开更多
A series of 17-yr equilibrium simulations using the NCAR COM3 (T42resolution) were performed to investigate the regional scale impacts of land cover change andincreasing CO_2 over China. Simulations with natural and c...A series of 17-yr equilibrium simulations using the NCAR COM3 (T42resolution) were performed to investigate the regional scale impacts of land cover change andincreasing CO_2 over China. Simulations with natural and current land cover at CO_2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in majorclimate fields (e.g. temperature and surface wind speed) on a 15-yr average following land coverchange. We also found increases in the maximum temperature and in the diurnal temperature range dueto land cover change. Increases in CO_2 affect both the maximum and minimum temperature so thatchanges in the diurnal range are small. Both land cover change and CO_2 change also impact thefrequency distribution of precipitation with increasing CO_2 tending to lead to more intenseprecipitation and land cover change leading to less intense precipitation―indeed, the impact ofland cover change typically had the opposite effect versus the impacts of CO_2. Our results providesupport for the inclusion of future land cover change scenarios in long-term transitory climatemodelling experiments of the 21st Century. Our results also support the inclusion of land surfacemodels that can represent future land cover changes resulting from an ecological response to naturalclimate variability or increasing CO_2. Overall, we show that land cover change can have asignificant impact on the regional scale climate of China, and that regionally, this impact is of asimilar magnitude to increases in CO_2 of up to about 430 ppmv. This means that that the impact ofland cover change must be accounted for in detection and attribution studies over China.展开更多
Features of the dominant modes of surface air temperature(SAT)on the intraseasonal timescale over the mid-highlatitude Eurasia(MHE)during boreal summer(June-September)are investigated based on the ERA5 reanalysis data...Features of the dominant modes of surface air temperature(SAT)on the intraseasonal timescale over the mid-highlatitude Eurasia(MHE)during boreal summer(June-September)are investigated based on the ERA5 reanalysis data from 1979 to 2016.The intraseasonal variability(ISV)of SAT over MHE is primarily characterized by an eastward propagation along 60°N,which is found to impact the regional weather in China,including summertime extreme hot and cool events.The forecast skill and potential predictability of the ISV of SAT over MHE are assessed for 5 dynamical models that have participated in the subseasonal-to-seasonal(S2 S)prediction project,by analyzing12 years’(1999-2010)model reforecast/hindcast data.By using the principal component(PC)index of the leading intraseasonal SAT modes as a predictand,we found that the forecast skill for ISV of SAT can reach out to 11-17 days,and the ECMWF model exhibits the best score.All the S2 S models tend to show 1)a relatively higher skill for strong intraseasonal oscillation(ISO)cases,2)a systematic underestimate of the amplitude of the SAT ISV signal,and 3)different skills during different phases of ISO cases.Analysis of potential predictability based on the perfectmodel assumption reveals a 4-6-day skill gap for most models,and the skill gap also varies among different phases of ISO events.The results imply the need for continued development of operational forecasting systems to improve the actual prediction skills for the ISV of SAT over MHE.展开更多
A physical method,based on the simplification of surface radiation terms in remote sensing equations, has been suggested to retrieve the surface temperature,vertical temperature profile and surface emissivity from the...A physical method,based on the simplification of surface radiation terms in remote sensing equations, has been suggested to retrieve the surface temperature,vertical temperature profile and surface emissivity from the first eight channel observations of TIROS-N/HIRS2.Analyses of several examples indicate that this method can obtain much more accurate temperatures in the lower atmosphere than a statistical technique, and that the surface temperature and emissivity retrieved are also reasonable.展开更多
Atmospheric CO_(2) concentration is characterized by spatial inhomogeneity and seasonal variability.The response of surface air temperature(SAT)to the inhomogeneity in CO_(2) concentration globally and regionally rema...Atmospheric CO_(2) concentration is characterized by spatial inhomogeneity and seasonal variability.The response of surface air temperature(SAT)to the inhomogeneity in CO_(2) concentration globally and regionally remains elusive.In this study,the BCC-CSM2-MR climate model was used to investigate the differences in global SAT in response to the spatially inhomogeneous distribution of atmospheric CO_(2) concentration.The analysis was based on three historical experiments(Hist_1dCO_(2),Hist_2dCO_(2),and Hist_3dCO_(2))conducted separately under the forcing of globally homogeneous,zonally homogeneous,and wholly spatially inhomogeneous CO_(2) concentrations from 1850 to 2014,derived from 12 Earth System Models of the Coupled Model Intercomparison Project Phase 6.The simulation results revealed similar trends of evolution in the global mean SATs in the 20th century under the three CO_(2) concentration distributions,and showed that the simulated historical SATs considering the meridional inhomogeneity of CO_(2) concentration in Hist_2dCO_(2) and the wholly spatial inhomogeneity in Hist_3dCO_(2) were more consistent with the observations.Compared with the results of Hist_1dCO_(2),the SATs in Hist_2dCO_(2) were warmer over land in the mid–high latitudes of the Northern Hemisphere(NH)than over other land areas.Further consideration of the zonally inhomogeneous CO_(2) concentration in Hist_3dCO_(2) revealed generally colder SATs over the NH mid–high-latitude ocean than over land at the same latitudes,and even the zonal mean SATs in the NH were slightly colder than those in Hist_2dCO_(2).These differences are ascribed to the uneven distribution of CO_(2) concentration along the same latitude in the NH in Hist_3dCO_(2),which leads to strong large-scale fluctuations in the atmospheric circulation.Eurasia is the region with the highest concentration of atmospheric CO_(2),which leads to remarkable regional SAT warming owing to enhanced downward longwave radiation.Warmer SATs in Eurasia in winter will further strengthen the northwesterly winds over eastern Asia,resulting in an increase in sea ice and strengthened cold SAT anomalies over the northern North Pacific.The simulated varied responses of the atmospheric circulation and SAT to inhomogeneous CO_(2) forcing highlight the imperative need for refined representation of the inhomogeneity of the atmospheric CO_(2) distribution in climate models for more accurate assessment of climate change.展开更多
针对2007年6月—9月全球集合预报系统(THORPEX Interactive Grand Global Ensemble,TIGGE)多模式中的欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)、美国国家环境预报中心(National Centers for En...针对2007年6月—9月全球集合预报系统(THORPEX Interactive Grand Global Ensemble,TIGGE)多模式中的欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)、美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)、英国气象局(United Kingdom Meteorological Office,UKMO)及日本气象厅(Japan Meteorological Agency,JMA)这4个集合预报模式产品资料,对东亚地区地面2 m气温进行了贝叶斯模式平均(Bayesian model averaging,BMA)方法的概率预报研究,并与简单集合平均(ensemble mean,EMN)方法的概率预报进行对比,最终采用(continuous ranked probability score,CRPS)评分与均方根误差(root of mean square error,RMSE)评估BMA方法在概率预报和确定性预报方面的预报效果。研究表明,BMA方法可有效将单一的确定性预报向连续概率预报转化,并全面准确地描述大气的多种可能运动状态,同时提供概率预报和确定性预报。BMA方法在量化不确定性信息方面优于EMN方法,在一定程度上减小了预报的不确定性。就确定性预报效果而言,BMA方法的预报效果优于所有的单模式预报以及EMN方法,但会受到训练期长度和选取模式性能优劣的影响,其预报效果也会发生改变。展开更多
地球系统模式结果表明大气CO_(2)浓度的快速增加是气候变化重要的原因之一。卫星资料分析结果表明,大气CO_(2)浓度并非均一的,而是有明显的区域差异,以人类活动为主的碳排放会影响这一区域差异。这种空间差异如何影响区域地表气温对CO_...地球系统模式结果表明大气CO_(2)浓度的快速增加是气候变化重要的原因之一。卫星资料分析结果表明,大气CO_(2)浓度并非均一的,而是有明显的区域差异,以人类活动为主的碳排放会影响这一区域差异。这种空间差异如何影响区域地表气温对CO_(2)的敏感度,需要进一步深入系统的研究,利用地球系统模式BNU-ESM(Earth System Model of Beijing Normal University)进行数值模拟,并与观测数据进行比较,结果表明:在试验模拟结果2°C阈值内,非均匀CO_(2)浓度试验的CO_(2)浓度增加阈值范围小于均匀CO_(2)浓度试验结果,偏少约为4.3 ppm(106)。在区域尺度上,中国地表气温对CO_(2)敏感度普遍低于美国、欧洲以及北半球平均水平,这表明CO_(2)浓度空间差异对地表气温的敏感度的影响存在明显区域差异,很可能是CO_(2)浓度辐射效应与气候系统反馈过程的共同作用结果,这需要进一步研究。非均匀CO_(2)浓度对地表气温敏感度影响将会对碳中和目标下未来碳汇潜力精准估算提供科学支持。展开更多
基金supported by the National Postdoctoral Scientific Foundation(20080440342)the opening fund from the State Key Laboratory of Cryospheric Sciences,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences(SKLCS 08-07)
文摘Based on the number of snow cover days （NSCDs） and homogenized surface air temperature data for the period 1951-2004, this study performs the quantitative analysis on the sensitivity of NSCDs to surface air temperature over the Qinghai-Tibetan Plateau （QTP）. Results show that both the extreme sensitivity and sensitivity under current climate are higher in the edge than in the central area of the QTP. There exists a strong negative correlation between station＇s elevation and critical temperature, at which the sensitivity reaches extremum. The negative correlation between the elevation and the extreme sensitivity is not as strong as the former one. Currently, the climatological temperatures in quite a few stations do not reach the critical stage. The sensitivity at these stations will become greater under the current background of climate warming, which means NSCDs will be more sensitive to surface air temperature.
基金supported by National Natural Science Foundation of China (Grant No.40874047)supported by National Natural Science Foundation of China (Grant No.40975009)supported by the National Key Basic Research Program (Grant No. 2012CB417203)
文摘Using the Simple Biosphere Model （SiB2）, soil thermal properties （STP） were examined in a Tibetan prairie during the monsoon period to investigate ground surface temperature prediction. We improved the SiB2 model by incorporating a revised force-restore method （FRM） to take the vertical heterogeneity of soil thermal diffusivity （k） into account. The results indicate that （1） the revised FRM alleviates daytime overestimation and nighttime underestimation in modeled ground surface temperature （Tg）, and （2） its role in little rainfall events is significant because the vertical gradient of k increases with increasing surface evaporation. Since the original formula of thermal conductivity （A） in the SiB2 greatly underestimates soil thermal conductivity, we compared five Mgorithms of A involving soil moisture to investigate the cause of overestimation during the day and underestimation at night on the basis of the revised FRM. The results show that （1） the five algorithms significantly improve Tg prediction, especially in daytime, and （2） taking one of these five algorithms as an example, the simulated Tg values in the daytime are closer to the field measurements than those in the nighttime. The differences between modeled Tg and field measurements are mostly within the margin of error of -4-2 K during 3 August to 4 September 1998.
基金the National Natural Science Foundation of China (Grant Nos.42175142,42141017 and 41975112) for supporting our study。
文摘The increasing concentration of atmospheric CO_(2) since the Industrial Revolution has affected surface air temperature.However,the impact of the spatial distribution of atmospheric CO_(2) concentration on surface air temperature biases remains highly unclear.By incorporating the spatial distribution of satellite-derived atmospheric CO_(2) concentration in the Beijing Normal University Earth System Model,this study investigated the increase in surface air temperature since the Industrial Revolution in the Northern Hemisphere(NH) under historical conditions from 1976-2005.In comparison with the increase in surface temperature simulated using a uniform distribution of CO_(2),simulation with a nonuniform distribution of CO_(2)produced better agreement with the Climatic Research Unit(CRU) data in the NH under the historical condition relative to the baseline over the period 1901-30.Hemispheric June-July-August(JJA) surface air temperature increased by 1.28℃ ±0.29℃ in simulations with a uniform distribution of CO_(2),by 1.00℃±0.24℃ in simulations with a non-uniform distribution of CO_(2),and by 0.24℃ in the CRU data.The decrease in downward shortwave radiation in the non-uniform CO_(2) simulation was primarily attributable to reduced warming in Eurasia,combined with feedbacks resulting from increased leaf area index(LAI) and latent heat fluxes.These effects were more pronounced in the non-uniform CO_(2)simulation compared to the uniform CO_(2) simulation.Results indicate that consideration of the spatial distribution of CO_(2)concentration can reduce the overestimated increase in surface air temperature simulated by Earth system models.
文摘The massive lockdown of human socioeconomic activities and vehicle movements due to the COVID-19 pandemic in 2020 has resulted in an unprecedented reduction in pollutant gases such as Nitrogen Dioxide(NO_(2))and Carbon Monoxide(CO)as well as Land Surface Temperature(LST)in Amman as well as all countries around the globe.In this study,the spatial and temporal variability/stability of NO_(2),CO,and LST throughout the lockdown period over Amman city have been analyzed.The NO_(2) and CO column density values were acquired from Sentinel-5p while the LST data were obtained from MODIS satellite during the lockdown period from 20 March to 24 April in 2019,2020,and 2021.The statistical analysis showed an overall reduction in NO_(2) in 2020 by around 27% and 48% compared to 2019 and 2021,respectively.However,an increase of 7% in 2021 compared to 2019 was observed because almost all anthropogenic activities were allowed during the daytime.The temporal persistence showed almost constant NO2 values in 2020 over the study area throughout the lockdown period.In addition,a slight decrease in CO(around 1%)was recorded in 2020 and 2021 compared to the same period in 2019.Restrictions on human activities resulted in an evident drop in LST in 2020 by around 13%and 18% less than the 5-year average and 2021 respectively.The study concludes that due to the restrictions imposed on industrial activities and automobile movements in Amman city,an unprecedented reduction in NO_(2),CO,and LST was recorded.
文摘A series of 17-yr equilibrium simulations using the NCAR COM3 (T42resolution) were performed to investigate the regional scale impacts of land cover change andincreasing CO_2 over China. Simulations with natural and current land cover at CO_2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in majorclimate fields (e.g. temperature and surface wind speed) on a 15-yr average following land coverchange. We also found increases in the maximum temperature and in the diurnal temperature range dueto land cover change. Increases in CO_2 affect both the maximum and minimum temperature so thatchanges in the diurnal range are small. Both land cover change and CO_2 change also impact thefrequency distribution of precipitation with increasing CO_2 tending to lead to more intenseprecipitation and land cover change leading to less intense precipitation―indeed, the impact ofland cover change typically had the opposite effect versus the impacts of CO_2. Our results providesupport for the inclusion of future land cover change scenarios in long-term transitory climatemodelling experiments of the 21st Century. Our results also support the inclusion of land surfacemodels that can represent future land cover changes resulting from an ecological response to naturalclimate variability or increasing CO_2. Overall, we show that land cover change can have asignificant impact on the regional scale climate of China, and that regionally, this impact is of asimilar magnitude to increases in CO_2 of up to about 430 ppmv. This means that that the impact ofland cover change must be accounted for in detection and attribution studies over China.
基金Supported by the National Key Research and Development Program of China(2018YFC1505803 and 2018YFC1505905)Natural Science Foundation of Jiangsu Province(BK20210660 and BK20191404)National Natural Science Foundation of China(42088101)。
文摘Features of the dominant modes of surface air temperature(SAT)on the intraseasonal timescale over the mid-highlatitude Eurasia(MHE)during boreal summer(June-September)are investigated based on the ERA5 reanalysis data from 1979 to 2016.The intraseasonal variability(ISV)of SAT over MHE is primarily characterized by an eastward propagation along 60°N,which is found to impact the regional weather in China,including summertime extreme hot and cool events.The forecast skill and potential predictability of the ISV of SAT over MHE are assessed for 5 dynamical models that have participated in the subseasonal-to-seasonal(S2 S)prediction project,by analyzing12 years’(1999-2010)model reforecast/hindcast data.By using the principal component(PC)index of the leading intraseasonal SAT modes as a predictand,we found that the forecast skill for ISV of SAT can reach out to 11-17 days,and the ECMWF model exhibits the best score.All the S2 S models tend to show 1)a relatively higher skill for strong intraseasonal oscillation(ISO)cases,2)a systematic underestimate of the amplitude of the SAT ISV signal,and 3)different skills during different phases of ISO cases.Analysis of potential predictability based on the perfectmodel assumption reveals a 4-6-day skill gap for most models,and the skill gap also varies among different phases of ISO events.The results imply the need for continued development of operational forecasting systems to improve the actual prediction skills for the ISV of SAT over MHE.
文摘A physical method,based on the simplification of surface radiation terms in remote sensing equations, has been suggested to retrieve the surface temperature,vertical temperature profile and surface emissivity from the first eight channel observations of TIROS-N/HIRS2.Analyses of several examples indicate that this method can obtain much more accurate temperatures in the lower atmosphere than a statistical technique, and that the surface temperature and emissivity retrieved are also reasonable.
基金Supported by the National Natural Science Foundation of China(42230608).
文摘Atmospheric CO_(2) concentration is characterized by spatial inhomogeneity and seasonal variability.The response of surface air temperature(SAT)to the inhomogeneity in CO_(2) concentration globally and regionally remains elusive.In this study,the BCC-CSM2-MR climate model was used to investigate the differences in global SAT in response to the spatially inhomogeneous distribution of atmospheric CO_(2) concentration.The analysis was based on three historical experiments(Hist_1dCO_(2),Hist_2dCO_(2),and Hist_3dCO_(2))conducted separately under the forcing of globally homogeneous,zonally homogeneous,and wholly spatially inhomogeneous CO_(2) concentrations from 1850 to 2014,derived from 12 Earth System Models of the Coupled Model Intercomparison Project Phase 6.The simulation results revealed similar trends of evolution in the global mean SATs in the 20th century under the three CO_(2) concentration distributions,and showed that the simulated historical SATs considering the meridional inhomogeneity of CO_(2) concentration in Hist_2dCO_(2) and the wholly spatial inhomogeneity in Hist_3dCO_(2) were more consistent with the observations.Compared with the results of Hist_1dCO_(2),the SATs in Hist_2dCO_(2) were warmer over land in the mid–high latitudes of the Northern Hemisphere(NH)than over other land areas.Further consideration of the zonally inhomogeneous CO_(2) concentration in Hist_3dCO_(2) revealed generally colder SATs over the NH mid–high-latitude ocean than over land at the same latitudes,and even the zonal mean SATs in the NH were slightly colder than those in Hist_2dCO_(2).These differences are ascribed to the uneven distribution of CO_(2) concentration along the same latitude in the NH in Hist_3dCO_(2),which leads to strong large-scale fluctuations in the atmospheric circulation.Eurasia is the region with the highest concentration of atmospheric CO_(2),which leads to remarkable regional SAT warming owing to enhanced downward longwave radiation.Warmer SATs in Eurasia in winter will further strengthen the northwesterly winds over eastern Asia,resulting in an increase in sea ice and strengthened cold SAT anomalies over the northern North Pacific.The simulated varied responses of the atmospheric circulation and SAT to inhomogeneous CO_(2) forcing highlight the imperative need for refined representation of the inhomogeneity of the atmospheric CO_(2) distribution in climate models for more accurate assessment of climate change.
文摘针对2007年6月—9月全球集合预报系统(THORPEX Interactive Grand Global Ensemble,TIGGE)多模式中的欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)、美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)、英国气象局(United Kingdom Meteorological Office,UKMO)及日本气象厅(Japan Meteorological Agency,JMA)这4个集合预报模式产品资料,对东亚地区地面2 m气温进行了贝叶斯模式平均(Bayesian model averaging,BMA)方法的概率预报研究,并与简单集合平均(ensemble mean,EMN)方法的概率预报进行对比,最终采用(continuous ranked probability score,CRPS)评分与均方根误差(root of mean square error,RMSE)评估BMA方法在概率预报和确定性预报方面的预报效果。研究表明,BMA方法可有效将单一的确定性预报向连续概率预报转化,并全面准确地描述大气的多种可能运动状态,同时提供概率预报和确定性预报。BMA方法在量化不确定性信息方面优于EMN方法,在一定程度上减小了预报的不确定性。就确定性预报效果而言,BMA方法的预报效果优于所有的单模式预报以及EMN方法,但会受到训练期长度和选取模式性能优劣的影响,其预报效果也会发生改变。
文摘地球系统模式结果表明大气CO_(2)浓度的快速增加是气候变化重要的原因之一。卫星资料分析结果表明,大气CO_(2)浓度并非均一的,而是有明显的区域差异,以人类活动为主的碳排放会影响这一区域差异。这种空间差异如何影响区域地表气温对CO_(2)的敏感度,需要进一步深入系统的研究,利用地球系统模式BNU-ESM(Earth System Model of Beijing Normal University)进行数值模拟,并与观测数据进行比较,结果表明:在试验模拟结果2°C阈值内,非均匀CO_(2)浓度试验的CO_(2)浓度增加阈值范围小于均匀CO_(2)浓度试验结果,偏少约为4.3 ppm(106)。在区域尺度上,中国地表气温对CO_(2)敏感度普遍低于美国、欧洲以及北半球平均水平,这表明CO_(2)浓度空间差异对地表气温的敏感度的影响存在明显区域差异,很可能是CO_(2)浓度辐射效应与气候系统反馈过程的共同作用结果,这需要进一步研究。非均匀CO_(2)浓度对地表气温敏感度影响将会对碳中和目标下未来碳汇潜力精准估算提供科学支持。
