The East Asian summer monsoon （EASM） is a distinctive component of the Asian climate system and critically influences the economy and society of the region.To understand the ability of AGCMs in capturing the major f...The East Asian summer monsoon （EASM） is a distinctive component of the Asian climate system and critically influences the economy and society of the region.To understand the ability of AGCMs in capturing the major features of EASM,10 models that participated in Coupled Model Intercomparison Project/Atmospheric Model Intercomparison Project （CMIP5/AMIP）,which used observational SST and sea ice to drive AGCMs during the period 1979-2008,were evaluated by comparing with observations and AMIP Ⅱ simulations.The results indicated that the multi-model ensemble （MME） of CMIP5/AMIP captures the main characteristics of precipitation and monsoon circulation,and shows the best skill in EASM simulation,better than the AMIP Ⅱ MME.As for the Meiyu/Changma/Baiyu rainbelt,the intensity of rainfall is underestimated in all the models.The biases are caused by a weak western Pacific subtropical high （WPSH） and accompanying eastward southwesterly winds in group Ⅰ models,and by a too strong and west-extended WPSH as well as westerly winds in group Ⅱ models.Considerable systematic errors exist in the simulated seasonal migration of rainfall,and the notable northward jumps and rainfall persistence remain a challenge for all the models.However,the CMIP5/AMIP MME is skillful in simulating the western North Pacific monsoon index （WNPMI）.展开更多
This study examines cloud radiative forcing （CRF） in the Asian monsoon region （0° 50°N, 60° 150°E） simulated by Intergovernmental Panel on Climate Change （IPCC） Fourth Assessment Report （AR4...This study examines cloud radiative forcing （CRF） in the Asian monsoon region （0° 50°N, 60° 150°E） simulated by Intergovernmental Panel on Climate Change （IPCC） Fourth Assessment Report （AR4） AMIP models. During boreal winter, no model realistically reproduces the larger long-wave cloud radiative forcing （LWCF） over the Tibet Plateau （TP） and only a couple of models reasonably capture the larger short-wave CRF （SWCF） to the east of the TP. During boreal summer, there are larger biases for central location and intensity of simulated CRF in active convective regions. The CRF biases are closely related to the rainfall biases in the models. Quantitative analysis further indicates that the correlation between simulated CRF and observations are not high, and that the biases and diversity in SWCF are larger than that in LWCF. The annual cycle of simulated CRF over East Asia （0°-50°N, 100°-145°E） is also examined. Though many models capture the basic annual cycle in tropics, strong LWCF and SWCF to the east of the TP beginning in early spring are underestimated by most models. As a whole, GFDL-CM2.1, MPI-ECHAM5, UKMO-HadGAM1, and MIROC3.2 （medres） perform well for CRF simulation in the Asian monsoon region, and the multi-model ensemble （MME） has improved results over the individual simulations. It is suggested that strengthening the physical parameterizations involved over the TP, and improving cumulus convection processes and model experiment design are crucial to CRF simulation in the Asian monsoon region.展开更多
The atmospheric angular momentum (AAM) functions in terms of contribution to polar wobble and length of day change, are calculated from the output data of GSM9603 global circulation model (GCM) of Japan Meteorological...The atmospheric angular momentum (AAM) functions in terms of contribution to polar wobble and length of day change, are calculated from the output data of GSM9603 global circulation model (GCM) of Japan Meteorological Agency (JMA), from the reanalysis data of the National Centers for the Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR), and from the operational objective analysis data of JMA, respectively. The comparison shows that during the period from 1985 to 1995, the values of the pressure terms in the equatorial components of AAM functions calculated from three data sets agree with each other better along 90°E longitude than along Greenwich meridian direction. The axial component of relative AAM function estimated from GSM 9603 agrees well with those from the other two data sets in terms of seasonal variations with the moderate amplitudes, but not so well with the composite axial component of relative AAM functions estimated from 23 GCM models anticipating in the first phase of AMIP. In addition, its interannual variation from 1979 to 1996 shows the main characteristics of ENSO evolution, just as does the axial component of relative AAM function estimated from NCEP reanalysis data except for the period of anomalous ENSO from 1991 to 1993.展开更多
用偏最小二乘(Partial Least Square,PLS)回归方法分析了1979~2018年影响亚马逊旱季(6~8月)降水年际变率的热带海面温度模态。第一海面温度模态解释了总方差的64%,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6~8月)热带东太平洋La ...用偏最小二乘(Partial Least Square,PLS)回归方法分析了1979~2018年影响亚马逊旱季(6~8月)降水年际变率的热带海面温度模态。第一海面温度模态解释了总方差的64%,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6~8月)热带东太平洋La Niña型海面温度异常演变。12月至次年2月热带东太平洋出现La Niña型海面温度冷异常;3~5月热带东太平洋冷异常增强,并在热带印度洋、热带北大西洋出现冷异常,在热带南大西洋有暖异常;6~8月热带东太平洋冷异常向东收缩;9~11月整个热带海面温度异常均快速衰退。第二海面温度模态解释了总方差的19%,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6~8月)中太平洋Modoki El Niño型增暖。12月至次年2月在热带中太平洋出现暖异常,印度洋和南大西洋同样也出现暖异常,热带中太平洋和南大西洋暖异常能持续到9~11月,而印度洋暖异常在9~11月衰减。这些结果表明,亚马逊旱季降水与热带海面温度的演变有关,当前期12月至次年2月出现La Niña(Modoki El Niño)事件、3~8月出现热带南北大西洋海面温度梯度负异常并且热带印度洋海面温度冷(暖)异常时,亚马逊旱季降水偏多。这两个海面温度模态对降水的总贡献与亚马逊旱季降水指数的相关关系高达0.92,说明亚马逊旱季降水年际变率与热带海面温度密切相关;而且这两个海面温度模态对亚马逊旱季降水的贡献还有明显的年代际变化,自1979年以来,海面温度对降水的贡献有下降趋势。还对海面温度影响亚马逊旱季降水年际变率的机制进行了分析,发现海面温度可以通过影响亚马逊地区的环流场、水汽输送以及大气对流层稳定性进而导致降水异常。第一海面温度模态能激发亚马逊低空北部气流辐合,高空北部气流辐散,容易形成异常的上升运动;同时,亚马逊对流层的异常湿静能收支也表明第一海面温度模态会使亚马逊地区对流层不稳定性增加;另外,第一海面温度模态还能使亚马逊北部出现异常水汽辐合,这都会导致亚马逊北部降水增加。第二海面温度模态激发亚马逊东南部气流辐合上升,西部气流辐散下沉;亚马逊对流层的异常湿静能收支显示第二海面温度模态使亚马逊东南部气层不稳定,中部稳定,这导致亚马逊东部降水增加。最后选取了大气模式比较计划(Atmospheric Model Intercomparison Project,AMIP6)中7个模式数据的集合平均对以上结果进行验证,发现无论是海面温度模态还是影响机制,都与再分析资料的结果基本一致。这说明以上结果是可信的,热带海面温度确实与亚马逊旱季降水有密切关系。展开更多
The outputs of the Chinese Academy of Sciences(CAS) Flexible Global Ocean–Atmosphere–Land System(FGOALS-f3-L) model for the baseline experiment of the Atmospheric Model Intercomparison Project simulation in the Diag...The outputs of the Chinese Academy of Sciences(CAS) Flexible Global Ocean–Atmosphere–Land System(FGOALS-f3-L) model for the baseline experiment of the Atmospheric Model Intercomparison Project simulation in the Diagnostic,Evaluation and Characterization of Klima common experiments of phase 6 of the Coupled Model Intercomparison Project(CMIP6) are described in this paper. The CAS FGOALS-f3-L model, experiment settings, and outputs are all given. In total,there are three ensemble experiments over the period 1979–2014, which are performed with different initial states. The model outputs contain a total of 37 variables and include the required three-hourly mean, six-hourly transient, daily and monthly mean datasets. The baseline performances of the model are validated at different time scales. The preliminary evaluation suggests that the CAS FGOALS-f3-L model can capture the basic patterns of atmospheric circulation and precipitation well, including the propagation of the Madden–Julian Oscillation, activities of tropical cyclones, and the characterization of extreme precipitation. These datasets contribute to the benchmark of current model behaviors for the desired continuity of CMIP.展开更多
The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2...The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(Tas) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(Ts) over the TP. The cold biases are larger in Tasthan in Ts, and are larger over the western TP. By decomposing the Tsbias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature bias.Strong negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models.展开更多
The seasonal variations of the Asian monsoon were explored by applying the atmospheric general circulation model R42L9 that was developed recently at the State Key Laboratory of Numerical Modeling for At...The seasonal variations of the Asian monsoon were explored by applying the atmospheric general circulation model R42L9 that was developed recently at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP/CAS). The 20-yr (1979–1998) simulation was done using the prescribed 20-yr monthly SST and sea-ice data as required by Atmospheric Model Intercomparison Project (AMIP) II in the model. The monthly precipitation and monsoon circulations were analyzed and compared with the observations to validate the model’s performance in simulating the climatological mean and seasonal variations of the Asian monsoon. The results show that the model can capture the main features of the spatial distribution and the temporal evolution of precipitation in the Indian and East Asian monsoon areas. The model also reproduced the basic patterns of monsoon circulation. However, some biases exist in this model. The simulation of the heating over the Tibetan Plateau in summer was too strong. The overestimated heating caused a stronger East Asian monsoon and a weaker Indian monsoon than the observations. In the circulation ?elds, the South Asia high was stronger and located over the Tibetan Plateau. The western Paci?c subtropical high was extended westward, which is in accordance with the observational results when the heating over the Tibetan Plateau is stronger. Consequently, the simulated rainfall around this area and in northwest China was heavier than in observations, but in the Indian monsoon area and west Paci?c the rainfall was somewhat de?cient.展开更多
The sensitivity of the representation of the global monsoon annual cycle to horizontal resolution is compared in three AGCMs： the Met Office Unified Model-Global Atmosphere 3.0; the Meteorological Research Institute ...The sensitivity of the representation of the global monsoon annual cycle to horizontal resolution is compared in three AGCMs： the Met Office Unified Model-Global Atmosphere 3.0; the Meteorological Research Institute AGCM3; and the Global High Resolution AGCM from the Geophysical Fluid Dynamics Laboratory. For each model, we use two horizon- tal resolution configurations for the period 1998-2008. Increasing resolution consistently improves simulated precipitation and low-level circulation of the annual mean and the first two annual cycle modes, as measured by the pattern correla- tion coefficient and equitable threat score. Improvements in simulating the summer monsoon onset and withdrawal are region-dependent. No consistent response to resolution is found in simulating summer monsoon retreat. Regionally, in- creased resolution reduces the positive bias in simulated annual mean precipitation, the two annual-cycle modes over the West African monsoon and Northwestern Pacific monsoon. An overestimation of the solstitial mode and an underestimation of the equinoctial asymmetric mode of the East Asian monsoon axe reduced in all high-resolution configurations. Systematic errors exist in lower-resolution models for simulating the onset and withdrawal of the summer monsoon. Higher resolution models consistently improve the early summer monsoon onset over East Asia and West Africa, but substantial differences exist in the responses over the Indian monsoon region, where biases differ across the three low-resolution AGCMs. This study demonstrates the importance of a multi-model comparison when examining the added value of resolution and the importance of model physical parameterizations for simulation of the Indian monsoon.展开更多
The South Asian High(SAH) is one of the most important components of the Asian summer monsoon system. To understand the ability of state-of-the-art general circulation models(GCMs) to capture the major characteristics...The South Asian High(SAH) is one of the most important components of the Asian summer monsoon system. To understand the ability of state-of-the-art general circulation models(GCMs) to capture the major characteristics of the SAH, the authors evaluate 18 atmospheric models that participated in the Coupled Model Intercomparison Project Phase 5/Atmospheric Model Intercomparison Project(CMIP5/AMIP). Results show that the multi-model ensemble(MME) mean is able to capture the climatological pattern of the SAH, although its intensity is slightly underestimated. For the interannual variability of the SAH, the MME exhibits good correlation with the reanalysis for the area and intensity index, but poor skill in capturing the east-west oscillation of the SAH. For the interdecadal trend, the MME shows pronounced increasing trends from 1985 to 2008 for the area and intensity indexes, which is consistent with the reanalysis, but fails to capture the westward shift of the SAH center. The individual models show different capacities for capturing climatological patterns, interannual variability, and interdecadal trends of the SAH. Several models fail to capture the climatological pattern, while one model overestimates the intensity of the SAH. Most of the models show good correlations for interannual variability, but nearly half exhibit high root-mean-square difference(RMSD) values. Six models successfully capture the westward shift of the SAH center in the interdecadal trends, while other models fail. The possible causes of the systematic biases involved in several models are also discussed.展开更多
With the motivation to improve the simulation of the East Asian summer monsoon(EASM) in coupled climate models, oceanic data assimilation(DA) was used in CAS-ESM-C(Chinese Academy of Sciences–Earth System Model–Clim...With the motivation to improve the simulation of the East Asian summer monsoon(EASM) in coupled climate models, oceanic data assimilation(DA) was used in CAS-ESM-C(Chinese Academy of Sciences–Earth System Model–Climate Component) in this study. Observed sea surface temperature was assimilated into CAS-ESM-C. The climatology and interannual variability of the EASM simulated in CAS-ESM-C with DA were compared with a traditional AMIP-type run.Results showed that the climatological spatial pattern and annual cycle of precipitation in the western North Paci?c, and the ENSO-related and EASM-related EASM circulation and precipitation, were largely improved. As shown in this study, air–sea coupling is important for EASM simulation. In addition, oceanic DA synchronizes the coupled model with the real world without breaking the air–sea coupling process. These two successful factors make the assimilation experiment a more reasonable experimental design than traditional AMIP-type simulations.展开更多
基金supported by the National High Technology Research and Development Program of China (Grant No. 2010AA012305)the General Project of the National Natural Science Foundation of China (Grant No. 41275108)+1 种基金the National Basic Research Program of China (Grant No. 2010CB950504)the Fundamental Research Funds for the Central Universities (Grant No. 2012YBXS27)
文摘The East Asian summer monsoon （EASM） is a distinctive component of the Asian climate system and critically influences the economy and society of the region.To understand the ability of AGCMs in capturing the major features of EASM,10 models that participated in Coupled Model Intercomparison Project/Atmospheric Model Intercomparison Project （CMIP5/AMIP）,which used observational SST and sea ice to drive AGCMs during the period 1979-2008,were evaluated by comparing with observations and AMIP Ⅱ simulations.The results indicated that the multi-model ensemble （MME） of CMIP5/AMIP captures the main characteristics of precipitation and monsoon circulation,and shows the best skill in EASM simulation,better than the AMIP Ⅱ MME.As for the Meiyu/Changma/Baiyu rainbelt,the intensity of rainfall is underestimated in all the models.The biases are caused by a weak western Pacific subtropical high （WPSH） and accompanying eastward southwesterly winds in group Ⅰ models,and by a too strong and west-extended WPSH as well as westerly winds in group Ⅱ models.Considerable systematic errors exist in the simulated seasonal migration of rainfall,and the notable northward jumps and rainfall persistence remain a challenge for all the models.However,the CMIP5/AMIP MME is skillful in simulating the western North Pacific monsoon index （WNPMI）.
基金supported by the CAS project under Grant No. KZCX2-YW-Q11-01the Major State Basic Research Development Program of China under Grant No. 2006CB403607the National Natural Science Foundation of China (Grant Nos.40523001, 40821092, 40875034)
文摘This study examines cloud radiative forcing （CRF） in the Asian monsoon region （0° 50°N, 60° 150°E） simulated by Intergovernmental Panel on Climate Change （IPCC） Fourth Assessment Report （AR4） AMIP models. During boreal winter, no model realistically reproduces the larger long-wave cloud radiative forcing （LWCF） over the Tibet Plateau （TP） and only a couple of models reasonably capture the larger short-wave CRF （SWCF） to the east of the TP. During boreal summer, there are larger biases for central location and intensity of simulated CRF in active convective regions. The CRF biases are closely related to the rainfall biases in the models. Quantitative analysis further indicates that the correlation between simulated CRF and observations are not high, and that the biases and diversity in SWCF are larger than that in LWCF. The annual cycle of simulated CRF over East Asia （0°-50°N, 100°-145°E） is also examined. Though many models capture the basic annual cycle in tropics, strong LWCF and SWCF to the east of the TP beginning in early spring are underestimated by most models. As a whole, GFDL-CM2.1, MPI-ECHAM5, UKMO-HadGAM1, and MIROC3.2 （medres） perform well for CRF simulation in the Asian monsoon region, and the multi-model ensemble （MME） has improved results over the individual simulations. It is suggested that strengthening the physical parameterizations involved over the TP, and improving cumulus convection processes and model experiment design are crucial to CRF simulation in the Asian monsoon region.
基金the National Natural Science Foundation of China under Grant Nos. 49904002 and 40074004, the National Climbing Project of China
文摘The atmospheric angular momentum (AAM) functions in terms of contribution to polar wobble and length of day change, are calculated from the output data of GSM9603 global circulation model (GCM) of Japan Meteorological Agency (JMA), from the reanalysis data of the National Centers for the Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR), and from the operational objective analysis data of JMA, respectively. The comparison shows that during the period from 1985 to 1995, the values of the pressure terms in the equatorial components of AAM functions calculated from three data sets agree with each other better along 90°E longitude than along Greenwich meridian direction. The axial component of relative AAM function estimated from GSM 9603 agrees well with those from the other two data sets in terms of seasonal variations with the moderate amplitudes, but not so well with the composite axial component of relative AAM functions estimated from 23 GCM models anticipating in the first phase of AMIP. In addition, its interannual variation from 1979 to 1996 shows the main characteristics of ENSO evolution, just as does the axial component of relative AAM function estimated from NCEP reanalysis data except for the period of anomalous ENSO from 1991 to 1993.
文摘用偏最小二乘(Partial Least Square,PLS)回归方法分析了1979~2018年影响亚马逊旱季(6~8月)降水年际变率的热带海面温度模态。第一海面温度模态解释了总方差的64%,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6~8月)热带东太平洋La Niña型海面温度异常演变。12月至次年2月热带东太平洋出现La Niña型海面温度冷异常;3~5月热带东太平洋冷异常增强,并在热带印度洋、热带北大西洋出现冷异常,在热带南大西洋有暖异常;6~8月热带东太平洋冷异常向东收缩;9~11月整个热带海面温度异常均快速衰退。第二海面温度模态解释了总方差的19%,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6~8月)中太平洋Modoki El Niño型增暖。12月至次年2月在热带中太平洋出现暖异常,印度洋和南大西洋同样也出现暖异常,热带中太平洋和南大西洋暖异常能持续到9~11月,而印度洋暖异常在9~11月衰减。这些结果表明,亚马逊旱季降水与热带海面温度的演变有关,当前期12月至次年2月出现La Niña(Modoki El Niño)事件、3~8月出现热带南北大西洋海面温度梯度负异常并且热带印度洋海面温度冷(暖)异常时,亚马逊旱季降水偏多。这两个海面温度模态对降水的总贡献与亚马逊旱季降水指数的相关关系高达0.92,说明亚马逊旱季降水年际变率与热带海面温度密切相关;而且这两个海面温度模态对亚马逊旱季降水的贡献还有明显的年代际变化,自1979年以来,海面温度对降水的贡献有下降趋势。还对海面温度影响亚马逊旱季降水年际变率的机制进行了分析,发现海面温度可以通过影响亚马逊地区的环流场、水汽输送以及大气对流层稳定性进而导致降水异常。第一海面温度模态能激发亚马逊低空北部气流辐合,高空北部气流辐散,容易形成异常的上升运动;同时,亚马逊对流层的异常湿静能收支也表明第一海面温度模态会使亚马逊地区对流层不稳定性增加;另外,第一海面温度模态还能使亚马逊北部出现异常水汽辐合,这都会导致亚马逊北部降水增加。第二海面温度模态激发亚马逊东南部气流辐合上升,西部气流辐散下沉;亚马逊对流层的异常湿静能收支显示第二海面温度模态使亚马逊东南部气层不稳定,中部稳定,这导致亚马逊东部降水增加。最后选取了大气模式比较计划(Atmospheric Model Intercomparison Project,AMIP6)中7个模式数据的集合平均对以上结果进行验证,发现无论是海面温度模态还是影响机制,都与再分析资料的结果基本一致。这说明以上结果是可信的,热带海面温度确实与亚马逊旱季降水有密切关系。
基金funded by the National Key Research and development Program of China (Grant No. 2017YFA0604004)the National Natural Science Foundation of China (Grant Nos. 91737306, U1811464, 41530426, 91837101, 41730963, and 91637312)
文摘The outputs of the Chinese Academy of Sciences(CAS) Flexible Global Ocean–Atmosphere–Land System(FGOALS-f3-L) model for the baseline experiment of the Atmospheric Model Intercomparison Project simulation in the Diagnostic,Evaluation and Characterization of Klima common experiments of phase 6 of the Coupled Model Intercomparison Project(CMIP6) are described in this paper. The CAS FGOALS-f3-L model, experiment settings, and outputs are all given. In total,there are three ensemble experiments over the period 1979–2014, which are performed with different initial states. The model outputs contain a total of 37 variables and include the required three-hourly mean, six-hourly transient, daily and monthly mean datasets. The baseline performances of the model are validated at different time scales. The preliminary evaluation suggests that the CAS FGOALS-f3-L model can capture the basic patterns of atmospheric circulation and precipitation well, including the propagation of the Madden–Julian Oscillation, activities of tropical cyclones, and the characterization of extreme precipitation. These datasets contribute to the benchmark of current model behaviors for the desired continuity of CMIP.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91437219 and 91637312)the Third Tibetan Plateau Scientific Experiment (Grant No. GYHY201406001)+1 种基金the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (Grant No. QYZDY-SSW-DQC018)the Special Program for Applied Research on Super Computation of the NSFC–Guangdong Joint Fund (second phase)
文摘The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(Tas) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(Ts) over the TP. The cold biases are larger in Tasthan in Ts, and are larger over the western TP. By decomposing the Tsbias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature bias.Strong negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models.
文摘The seasonal variations of the Asian monsoon were explored by applying the atmospheric general circulation model R42L9 that was developed recently at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP/CAS). The 20-yr (1979–1998) simulation was done using the prescribed 20-yr monthly SST and sea-ice data as required by Atmospheric Model Intercomparison Project (AMIP) II in the model. The monthly precipitation and monsoon circulations were analyzed and compared with the observations to validate the model’s performance in simulating the climatological mean and seasonal variations of the Asian monsoon. The results show that the model can capture the main features of the spatial distribution and the temporal evolution of precipitation in the Indian and East Asian monsoon areas. The model also reproduced the basic patterns of monsoon circulation. However, some biases exist in this model. The simulation of the heating over the Tibetan Plateau in summer was too strong. The overestimated heating caused a stronger East Asian monsoon and a weaker Indian monsoon than the observations. In the circulation ?elds, the South Asia high was stronger and located over the Tibetan Plateau. The western Paci?c subtropical high was extended westward, which is in accordance with the observational results when the heating over the Tibetan Plateau is stronger. Consequently, the simulated rainfall around this area and in northwest China was heavier than in observations, but in the Indian monsoon area and west Paci?c the rainfall was somewhat de?cient.
基金jointly supported by the National Natural Science Foundation of China(Grant Nos.41420104006,41330423)Program of International S&T Cooperation under grant 2016YFE0102400+1 种基金the UK-China Research&Innovation Partnership Fund through the Met Office Climate Science for Service Partnership(CSSP)China as part of the Newton Fundfunded by an Independent Research Fellowship from the Natural Environment Research Council(Grant No.NE/L010976/1)
文摘The sensitivity of the representation of the global monsoon annual cycle to horizontal resolution is compared in three AGCMs： the Met Office Unified Model-Global Atmosphere 3.0; the Meteorological Research Institute AGCM3; and the Global High Resolution AGCM from the Geophysical Fluid Dynamics Laboratory. For each model, we use two horizon- tal resolution configurations for the period 1998-2008. Increasing resolution consistently improves simulated precipitation and low-level circulation of the annual mean and the first two annual cycle modes, as measured by the pattern correla- tion coefficient and equitable threat score. Improvements in simulating the summer monsoon onset and withdrawal are region-dependent. No consistent response to resolution is found in simulating summer monsoon retreat. Regionally, in- creased resolution reduces the positive bias in simulated annual mean precipitation, the two annual-cycle modes over the West African monsoon and Northwestern Pacific monsoon. An overestimation of the solstitial mode and an underestimation of the equinoctial asymmetric mode of the East Asian monsoon axe reduced in all high-resolution configurations. Systematic errors exist in lower-resolution models for simulating the onset and withdrawal of the summer monsoon. Higher resolution models consistently improve the early summer monsoon onset over East Asia and West Africa, but substantial differences exist in the responses over the Indian monsoon region, where biases differ across the three low-resolution AGCMs. This study demonstrates the importance of a multi-model comparison when examining the added value of resolution and the importance of model physical parameterizations for simulation of the Indian monsoon.
基金funded by the National Basic Research Program of China (Grant No. 2014CB953904)the National Natural Science Foundation of China (Grant Nos. 91337110, 41405091, and 41305065)the State Key Laboratory of Loess and Quaternary Geology (Grant No. SKLLQG1216)
文摘The South Asian High(SAH) is one of the most important components of the Asian summer monsoon system. To understand the ability of state-of-the-art general circulation models(GCMs) to capture the major characteristics of the SAH, the authors evaluate 18 atmospheric models that participated in the Coupled Model Intercomparison Project Phase 5/Atmospheric Model Intercomparison Project(CMIP5/AMIP). Results show that the multi-model ensemble(MME) mean is able to capture the climatological pattern of the SAH, although its intensity is slightly underestimated. For the interannual variability of the SAH, the MME exhibits good correlation with the reanalysis for the area and intensity index, but poor skill in capturing the east-west oscillation of the SAH. For the interdecadal trend, the MME shows pronounced increasing trends from 1985 to 2008 for the area and intensity indexes, which is consistent with the reanalysis, but fails to capture the westward shift of the SAH center. The individual models show different capacities for capturing climatological patterns, interannual variability, and interdecadal trends of the SAH. Several models fail to capture the climatological pattern, while one model overestimates the intensity of the SAH. Most of the models show good correlations for interannual variability, but nearly half exhibit high root-mean-square difference(RMSD) values. Six models successfully capture the westward shift of the SAH center in the interdecadal trends, while other models fail. The possible causes of the systematic biases involved in several models are also discussed.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences [grant number XDA19030403]the National Natural Science Foundation of China [grant numbers 41606027 and 41706028]+1 种基金the National Key R&D Program of China [grant number2017YFA0604201]the China Postdoctoral Science Foundation [grant number 2015M571095]
文摘With the motivation to improve the simulation of the East Asian summer monsoon(EASM) in coupled climate models, oceanic data assimilation(DA) was used in CAS-ESM-C(Chinese Academy of Sciences–Earth System Model–Climate Component) in this study. Observed sea surface temperature was assimilated into CAS-ESM-C. The climatology and interannual variability of the EASM simulated in CAS-ESM-C with DA were compared with a traditional AMIP-type run.Results showed that the climatological spatial pattern and annual cycle of precipitation in the western North Paci?c, and the ENSO-related and EASM-related EASM circulation and precipitation, were largely improved. As shown in this study, air–sea coupling is important for EASM simulation. In addition, oceanic DA synchronizes the coupled model with the real world without breaking the air–sea coupling process. These two successful factors make the assimilation experiment a more reasonable experimental design than traditional AMIP-type simulations.
