Atmospheric response to SST variability was estimated using generalized equilibrium feedback analysis （GEFA） in the SST EOF space with synthesis data from an idealized climate model. Results show that the GEFA atmos...Atmospheric response to SST variability was estimated using generalized equilibrium feedback analysis （GEFA） in the SST EOF space with synthesis data from an idealized climate model. Results show that the GEFA atmospheric response to the leading SST EOF modes is much more accurate and robust than the GEFA feedback matrix in physical space. Therefore, GEFA provides a practical method for assessing atmospheric response to large-scale SST anomalies in terms of the leading EOFs.展开更多
利用中国160个台站和NCEP再分析资料,引入综合分析气候反馈的统计方法——广义平衡反馈方法(GEFA),结合EOF、相关合成分析,探讨2009/2010年中国冬季气温异常型的成因。结果表明:2009/2010年中国冬季气温出现的东北冷西南暖分布型与同期...利用中国160个台站和NCEP再分析资料,引入综合分析气候反馈的统计方法——广义平衡反馈方法(GEFA),结合EOF、相关合成分析,探讨2009/2010年中国冬季气温异常型的成因。结果表明:2009/2010年中国冬季气温出现的东北冷西南暖分布型与同期海温异常及其相联系的大气环流异常有密切的关系。其中赤道中东太平洋海温异常的El Ni o型和赤道大西洋海温异常"正-负-正"三极型模态对2009/2010年中国冬季气温东北冷西南暖分布型有显著的强迫作用。上述海温异常型影响了大气环流异常,中高纬度地面偏北气流将冷空气输送到华北东北地区,致使该地区冬季气温偏低,同时中纬度西风增强,极地冷空气被迫盘踞在高纬,不能影响到西南地区,导致西南地区较常年更暖。展开更多
使用CCSM3(community climate system model version 3)模式的"淡水扰动试验"结果,对热盐环流强度减弱后中国区域冬、夏气候的不同响应特征进行了研究。结果表明:CCSM3可较为准确地再现中国附近区域表面气温及降水量的量值和...使用CCSM3(community climate system model version 3)模式的"淡水扰动试验"结果,对热盐环流强度减弱后中国区域冬、夏气候的不同响应特征进行了研究。结果表明:CCSM3可较为准确地再现中国附近区域表面气温及降水量的量值和分布形态。当热盐环流年平均强度减弱约80%之后,中国区域冬、夏季的表面气温与降水量显著降低,但冬、夏季的降低幅度与空间分布形态存在显著的差异。冬季的降温幅度较大且分布较为一致,平均降温幅度可达2.2℃,最大的降温幅度可达4℃;夏季的降温幅度相对较小且南北差异较大,平均降温幅度为1.3℃,最大的降温幅度为3℃。冬、夏季降水量的降低幅度都在6%左右,但其成因及其分布形态都存在显著差异。展开更多
The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North ...The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North Pacific subtropical mode waters using a general circulation model (LICOM1.0) for the period of 1958-2001. The model experiments focused on interannual variations of ocean dynamical processes under daily wind forcings and seasonal heat fluxes. The mode water formation region was defined by a potential vorticity minimum at outcrop locations. The model results show that two subduction rate maxima (>100 m/a) were located in the Subtropical Mode Water (STMW) and the Central Mode Water (CMW) formation regions. These regions are consistent with a climatologically calculated value. The subduction rate in the Eastern Subtropical Mode Water (ESTMW) formation region was smaller at about 75 m/a. The subduction rate shows clear interannual and decadal variations associated with oceanic dynamic variabilities. The average subduction rate of the STMW was much smaller during the period of 1981-1990 compared with other periods, while that of the CMW had a negative anomaly before 1975 and a positive anomaly after 1978. The variability agreed with Ekman and geostrophic advections and mixed layer depths. The interannual variability of the subduction rate for the ESTMW was smallest during 1970-1990, as a result of a weak wind stress curl. This paper explores how interannual signals from the atmosphere are stored in different parts of the ocean, and thus may contribute to a better understanding of feedback mechanisms for the Pacific Decadal Oscillation (PDO) event.展开更多
Most climate models project a weakening of the Walker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rai...Most climate models project a weakening of the Walker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rainfall increase compared to that of moisture increase, which leads to a decrease in ascending motion. Through an idealized aqua-planet simulation in which a zonal wavenumber-1 SST distribution is prescribed along the equator, we find that the Walker circulation is strengthened under a uniform 2-K SST warming, even though the global mean rainfall-moisture relationship remains the same. Further diagnosis shows that the ascending branch of the Walker cell is enhanced in the upper troposphere but weakened in the lower troposphere. As a result, a ＂double-cell＂ circulation change pattern with a clockwise （anti-clockwise） circulation anomaly in the upper （lower） troposphere forms, and the upper tropospheric circulation change dominates. The mechanism for the formation of the ＂double cell＂ circulation pattern is attributed to a larger （smaller） rate of increase of diabatic heating than static stability in the upper （lower） troposphere. The result indicates that the future change of the Walker circulation cannot simply be interpreted based on a global mean moisture budget argument.展开更多
By using the observed monthly mean data over 160 stations of China and NCAR/NCEP reanalysis data, the generalized equilibrium feedback assessment(GEFA) method, combined with the methods of EOF analysis, correlation an...By using the observed monthly mean data over 160 stations of China and NCAR/NCEP reanalysis data, the generalized equilibrium feedback assessment(GEFA) method, combined with the methods of EOF analysis, correlation and composite analysis, is used to explore the influence of different SST modes on a wintertime air temperature pattern in which it is cold in the northeast and warm in the southwest in China. The results show that the 2009/2010 winter air temperature oscillation mode between the northern and southern part of China is closely related to the corresponding sea surface temperature anomalies(SSTA) and its associated atmospheric circulation anomalies. Exhibiting warming in Northeast China and cooling in Southwest China, the mode is significantly forced by the El Nio mode and the North Atlantic SSTA mode, which have three poles. Under the influence of SSTA modes, the surface northerly flow transported cold air to North and Northeast China, resulting in low temperatures in the regions. Meanwhile, the mid-latitude westerlies intensify and the polar cold air stays in high latitudes and cannot affect the Southwest China, resulting in the warming there.展开更多
This paper presents a case study of mesoscale convective band （MCB） development along a quasi-stationary front over the Seout metropolitan area.The MCB,which initiated on 1500 UTC 20 September 2010 and ended on 1400...This paper presents a case study of mesoscale convective band （MCB） development along a quasi-stationary front over the Seout metropolitan area.The MCB,which initiated on 1500 UTC 20 September 2010 and ended on 1400 UTC 21 September 2010,produced a total precipitation amount of 259.5 mm.The MCB development occurred during a period of tropopause folding in the upper level and moisture advection with a low-level jet.The analyses show that the evolution of the MCB can be classified into five periods：（1） the cell-forming period,when convection initiated; （2） the frontogenetic period,when the stationary front formed over the Korean peninsula; （3） the quasi-stationary period,when the convective band remained over Seoul for 3 h; （4） the mature period,when the cloud cover was largest and the precipitation rate was greater than 90 mm h-1; and （5） the dissipating period,when the MCB diminished and disappeared.The synoptic,thermodynamic,and dynamic analyses show that the MCB maintained its longevity by a tilted updraft,which headed towards a positive PV anomaly.Precipitation was concentrated under this area,where a tilted ascending southwesterly converged with a tilted ascending northeasterly,at the axis of cyclonic rotation.The formation of the convective cell was attributed in part by tropopause folding,which enhanced the cyclonic vorticity at the surface,and by the low-level convergence of warm moist air and upperlevel divergence.The southwesterly flow ascended in a region with high moisture content and strong relative vorticity that maintained the development of an MCB along the quasi-stationary front.展开更多
Erratum to:Lee,Y.-H.,G.Lee,S.Joo,and K.-D.Ahn,2018:Observational study of surface wind along a sloping surface over mountainous terrain during winter.Adv.Atmos.Sci.,35(3),276−284,https://doi.org/10.1007/s00376-017-707...Erratum to:Lee,Y.-H.,G.Lee,S.Joo,and K.-D.Ahn,2018:Observational study of surface wind along a sloping surface over mountainous terrain during winter.Adv.Atmos.Sci.,35(3),276−284,https://doi.org/10.1007/s00376-017-7075-5.展开更多
Tree-ring based temperature reconstructions have successfully inferred the past inter-annual to millennium scales summer temperature variability. A clear relationship between annual and summer temperatures can provide...Tree-ring based temperature reconstructions have successfully inferred the past inter-annual to millennium scales summer temperature variability. A clear relationship between annual and summer temperatures can provide insights into tile variability of past annual mean tem- perature from the reconstructed summer temperature. However, how similar are summer and annual temperatures is to a large extent still unknown. This study aims at investigating the relationship between annual and summer temperatures at different timescales in central Sweden during the last millennium. The temperature variability in central Sweden can represent large parts of Scandinavia which has been a key region for dendroclimatological research. The observed annual and summer temperatures during 1901-2005 were firstly decomposed into different frequency bands using ensemble empirical mode decomposition （EEMD） method, and then the scale-dependent relationship was quantified using Pearson correlation coefficients. The relationship between the observed annual and summer temperatures determined by the instrumental data was subsequently used to evaluate 7 climate models. The model with the best performance was used to infer the relationship for the last millennium. The results show that the relationship between the observed annual and summer temperatures becomes stronger as the timescale increases, except for the 4--16 years timescales at which it does not show any relationship. The summer temperature variability at short timescales （2--4 years） shows much higher variance than the annual variability, while the annual temperature variability at long timescales （〉32 years） has a much higher variance than the summer one. During the last millennium, the simulated summer temperature also shows higher variance at the short timescales （2-4 years） and lower variance at the long timescales （〉1024 years） than those of the annual temperature. The relationship between the two temperatures is generally close at the long timescales, and weak at the short timescales. Overall the summer temperature variability cannot well reflect the annual mean temperature variability for the study region during both the 20th century and the last millennium. Furthermore, all the climate models examined overestimate the annual mean temperature variance at the 2--4 years timescales, which indicates that the overestimate could be one of reasons why the volcanic eruption induced cooling is larger in climate models than in proxy data.展开更多
This paper introduces a new approach for the initialization of ensemble numerical forecasting： Dynamic Analogue Initialization （DAI）. DAI assumes that the best model state trajectories for the past provide the init...This paper introduces a new approach for the initialization of ensemble numerical forecasting： Dynamic Analogue Initialization （DAI）. DAI assumes that the best model state trajectories for the past provide the initial conditions for the best forecasts in the future. As such, DAI performs the ensemble forecast using the best analogues from a full size ensemble. As a pilot study, the Lorenz63 and Lorenz96 models were used to test DAI＇s effectiveness independently. Results showed that DAI can improve the forecast significantly. Especially in lower-dimensional systems, DAI can reduce the forecast RMSE by ~50% compared to the Monte Carlo forecast （MC）. This improvement is because DAI is able to recognize the direction of the analysis error through the embedding process and therefore selects those good trajectories with reduced initial error. Meanwhile, a potential improvement of DAI is also proposed, and that is to find the optimal range of embedding time based on the error＇s growing speed.展开更多
Using 32 CMIP5（Coupled Model Intercomparison Project Phase 5） models, this study examines the veracity in the simulation of cloud amount and their radiative effects（CREs） in the historical run driven by observed e...Using 32 CMIP5（Coupled Model Intercomparison Project Phase 5） models, this study examines the veracity in the simulation of cloud amount and their radiative effects（CREs） in the historical run driven by observed external radiative forcing for 1850-2005, and their future changes in the RCP（Representative Concentration Pathway） 4.5 scenario runs for2006-2100. Validation metrics for the historical run are designed to examine the accuracy in the representation of spatial patterns for climatological mean, and annual and interannual variations of clouds and CREs. The models show large spread in the simulation of cloud amounts, specifically in the low cloud amount. The observed relationship between cloud amount and the controlling large-scale environment are also reproduced diversely by various models. Based on the validation metrics,four models-ACCESS1.0, ACCESS1.3, Had GEM2-CC, and Had GEM2-ES-are selected as best models, and the average of the four models performs more skillfully than the multimodel ensemble average.All models project global-mean SST warming at the increase of the greenhouse gases, but the magnitude varies across the simulations between 1 and 2 K, which is largely attributable to the difference in the change of cloud amount and distribution. The models that simulate more SST warming show a greater increase in the net CRE due to reduced low cloud and increased incoming shortwave radiation, particularly over the regions of marine boundary layer in the subtropics. Selected best-performing models project a significant reduction in global-mean cloud amount of about-0.99% K^-1and net radiative warming of 0.46 W m^-2K^-1, suggesting a role of positive feedback to global warming.展开更多
That a model has sensitivity responses to parameter uncertainties is a key concept in implementing model parameter es- timation using filtering theory and methodology. Depending on the nature of associated physics and...That a model has sensitivity responses to parameter uncertainties is a key concept in implementing model parameter es- timation using filtering theory and methodology. Depending on the nature of associated physics and characteristic variability of the fluid in a coupled system, the response time scales of a model to parameters can be different, from hourly to decadal. Unlike state estimation, where the update frequency is usually linked with observational frequency, the update frequency for parameter estimation must be associated with the time scale of the model sensitivity response to the parameter being esti- mated. Here, with a simple coupled model, the impact of model sensitivity response time scales on coupled model parameter estimation is studied. The model includes characteristic synoptic to decadal scales by coupling a long-term varying deep ocean with a slow-varying upper ocean forced by a chaotic atmosphere. Results show that, using the update frequency deter- mined by the model sensitivity response time scale, both the reliability and quality of parameter estimation can be improved significantly, and thus the estimated parameters make the model more consistent with the observation. These simple model results provide a guideline for when real observations are used to optimize the parameters in a coupled general circulation model for improving climate analysis and prediction initialization.展开更多
The exchange of energy and water between the lithosphere and atmosphere mainly takes place at the ground surface. Therefore, freeze/thaw condition at the ground surface is an important factor in ex- amining the intera...The exchange of energy and water between the lithosphere and atmosphere mainly takes place at the ground surface. Therefore, freeze/thaw condition at the ground surface is an important factor in ex- amining the interactions between the land surface and atmosphere. Based on the observation data obtained by CEOP/CAMP-Tibet, the diurnal freeze/thaw cycles of the ground surface near Naqu, central Tibetan Plateau was preliminarily analyzed. The results show that the surface layer was completely frozen for approximately one month. However, the time that the ground surface experienced diurnal freeze/thaw cycles was about 6 months. The high frequency of freeze/thaw cycles at the ground surface significantly influences water and energy exchanges between ground and atmosphere over half a year. The interaction processes between the ground and atmosphere under different soil conditions (such as complete thaw, complete freeze and diurnal freeze/thaw cycles) are issues worthy of further examina- tion.展开更多
Based on transient simulation of the last deglaciation(significant global warming period)using a fully coupled model and sensitivity experiment,we show explicitly how the thermohaline circulation(THC)affects the clima...Based on transient simulation of the last deglaciation(significant global warming period)using a fully coupled model and sensitivity experiment,we show explicitly how the thermohaline circulation(THC)affects the climate of China,especially during periods of abrupt climate change.The simulated evolution of the Chinese climate was consistent with the paleoclimate record during the last deglaciation.For example,the whole Chinese region warmed significantly during the BФlling-AllerФd warming event(BA).When the magnitude of the THC was reduced in the sensitivity experiment during BA,warming of the Chinese region was greatly affected.Our work shows that in addition to orbital forcing and greenhouse gases,the THC is an important factor influencing climate change in China at the century scale.展开更多
Atlantic thermohaline circulation(THC) is a key component of the Earth Climate System and identification of its changes during the 20th Century is critical to the understanding of its variation characteristics and the...Atlantic thermohaline circulation(THC) is a key component of the Earth Climate System and identification of its changes during the 20th Century is critical to the understanding of its variation characteristics and the corresponding climatic impacts.Previous researches have been inconclusive,with the results varying depending on the approach used to measure THC.The results for the two established approaches for measurement of the phenomenon(direct observation and indirect reconstruction) are contradictive(weakening and non-weakening),and their credibility needs improving.Based on the tight relationship between THC anomaly and "see-saw" intensities of Sea Surface Temperature(SST) and Surface Air Temperature(SAT),we first diagnose their quantitative relationship in the model experiments,which is corresponding to its two possible scenarios,and then reconstruct the changes of THC during the 20th Century respectively with multiple observed datasets of SST and SAT.Model results show that THC anomaly and SST/SAT "see-saw" intensities are well correlated in timescales longer than 10/40 years under scenarios of weakening/non-weakening respectively.Two kinds of reconstructions here are consistent with each other,and we propose that THC has undergone a 2-cycle oscillation with inter-decadal scale since the Industrial Revolution with a magnitude of about 1 Sv.The transformation times of decadal trend are around the mid-1910s,the 1940s,and the mid-1970s.This research further validates the main results of previous reconstructions,and points out that THC does not have a long-term weakening during the 20th Century.展开更多
基金supported by National Natural Science Foundation of China 40830106the 111 Project of China (No. B07036)+1 种基金Ministry of Science and Technology of China (No. GYHY200906016)US Department of Environment (DOE 144 KQ65)
文摘Atmospheric response to SST variability was estimated using generalized equilibrium feedback analysis （GEFA） in the SST EOF space with synthesis data from an idealized climate model. Results show that the GEFA atmospheric response to the leading SST EOF modes is much more accurate and robust than the GEFA feedback matrix in physical space. Therefore, GEFA provides a practical method for assessing atmospheric response to large-scale SST anomalies in terms of the leading EOFs.
文摘利用中国160个台站和NCEP再分析资料,引入综合分析气候反馈的统计方法——广义平衡反馈方法(GEFA),结合EOF、相关合成分析,探讨2009/2010年中国冬季气温异常型的成因。结果表明:2009/2010年中国冬季气温出现的东北冷西南暖分布型与同期海温异常及其相联系的大气环流异常有密切的关系。其中赤道中东太平洋海温异常的El Ni o型和赤道大西洋海温异常"正-负-正"三极型模态对2009/2010年中国冬季气温东北冷西南暖分布型有显著的强迫作用。上述海温异常型影响了大气环流异常,中高纬度地面偏北气流将冷空气输送到华北东北地区,致使该地区冬季气温偏低,同时中纬度西风增强,极地冷空气被迫盘踞在高纬,不能影响到西南地区,导致西南地区较常年更暖。
文摘使用CCSM3(community climate system model version 3)模式的"淡水扰动试验"结果,对热盐环流强度减弱后中国区域冬、夏气候的不同响应特征进行了研究。结果表明:CCSM3可较为准确地再现中国附近区域表面气温及降水量的量值和分布形态。当热盐环流年平均强度减弱约80%之后,中国区域冬、夏季的表面气温与降水量显著降低,但冬、夏季的降低幅度与空间分布形态存在显著的差异。冬季的降温幅度较大且分布较为一致,平均降温幅度可达2.2℃,最大的降温幅度可达4℃;夏季的降温幅度相对较小且南北差异较大,平均降温幅度为1.3℃,最大的降温幅度为3℃。冬、夏季降水量的降低幅度都在6%左右,但其成因及其分布形态都存在显著差异。
基金Supported by the National Natural Science Foundation of China (Nos. 40906005, 40830106, 40730953, GYHY201106017)the National Basic Research Program of China (973 Program) (No. 2010CB428504)the National Key Technologies Research and Development Program of China (No. 2009BAC51B01)
文摘The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North Pacific subtropical mode waters using a general circulation model (LICOM1.0) for the period of 1958-2001. The model experiments focused on interannual variations of ocean dynamical processes under daily wind forcings and seasonal heat fluxes. The mode water formation region was defined by a potential vorticity minimum at outcrop locations. The model results show that two subduction rate maxima (>100 m/a) were located in the Subtropical Mode Water (STMW) and the Central Mode Water (CMW) formation regions. These regions are consistent with a climatologically calculated value. The subduction rate in the Eastern Subtropical Mode Water (ESTMW) formation region was smaller at about 75 m/a. The subduction rate shows clear interannual and decadal variations associated with oceanic dynamic variabilities. The average subduction rate of the STMW was much smaller during the period of 1981-1990 compared with other periods, while that of the CMW had a negative anomaly before 1975 and a positive anomaly after 1978. The variability agreed with Ekman and geostrophic advections and mixed layer depths. The interannual variability of the subduction rate for the ESTMW was smallest during 1970-1990, as a result of a weak wind stress curl. This paper explores how interannual signals from the atmosphere are stored in different parts of the ocean, and thus may contribute to a better understanding of feedback mechanisms for the Pacific Decadal Oscillation (PDO) event.
基金sponsored by the China National 973 Program (Grant No.2015CB453200)the National Natural Science Foundation of China (Grant No.41475084)+2 种基金the China Scholarship Councilthe Office of Naval Research (ONR,Grant Nos.N00014-1210450 and ARCP2013-27NSY-Liu)partially sponsored by the Japan Agency for Marine-Earth Science and Technology
文摘Most climate models project a weakening of the Walker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rainfall increase compared to that of moisture increase, which leads to a decrease in ascending motion. Through an idealized aqua-planet simulation in which a zonal wavenumber-1 SST distribution is prescribed along the equator, we find that the Walker circulation is strengthened under a uniform 2-K SST warming, even though the global mean rainfall-moisture relationship remains the same. Further diagnosis shows that the ascending branch of the Walker cell is enhanced in the upper troposphere but weakened in the lower troposphere. As a result, a ＂double-cell＂ circulation change pattern with a clockwise （anti-clockwise） circulation anomaly in the upper （lower） troposphere forms, and the upper tropospheric circulation change dominates. The mechanism for the formation of the ＂double cell＂ circulation pattern is attributed to a larger （smaller） rate of increase of diabatic heating than static stability in the upper （lower） troposphere. The result indicates that the future change of the Walker circulation cannot simply be interpreted based on a global mean moisture budget argument.
基金Specialized Science Project for Public Welfare Industries(Meteorology)(GYHY200906016)State Key Program of National Natural Science Foundation of China(41230528)
文摘By using the observed monthly mean data over 160 stations of China and NCAR/NCEP reanalysis data, the generalized equilibrium feedback assessment(GEFA) method, combined with the methods of EOF analysis, correlation and composite analysis, is used to explore the influence of different SST modes on a wintertime air temperature pattern in which it is cold in the northeast and warm in the southwest in China. The results show that the 2009/2010 winter air temperature oscillation mode between the northern and southern part of China is closely related to the corresponding sea surface temperature anomalies(SSTA) and its associated atmospheric circulation anomalies. Exhibiting warming in Northeast China and cooling in Southwest China, the mode is significantly forced by the El Nio mode and the North Atlantic SSTA mode, which have three poles. Under the influence of SSTA modes, the surface northerly flow transported cold air to North and Northeast China, resulting in low temperatures in the regions. Meanwhile, the mid-latitude westerlies intensify and the polar cold air stays in high latitudes and cannot affect the Southwest China, resulting in the warming there.
基金funded by the Korea Meteorological Administration Research and Development Program under grant CATER 2012-2072
文摘This paper presents a case study of mesoscale convective band （MCB） development along a quasi-stationary front over the Seout metropolitan area.The MCB,which initiated on 1500 UTC 20 September 2010 and ended on 1400 UTC 21 September 2010,produced a total precipitation amount of 259.5 mm.The MCB development occurred during a period of tropopause folding in the upper level and moisture advection with a low-level jet.The analyses show that the evolution of the MCB can be classified into five periods：（1） the cell-forming period,when convection initiated; （2） the frontogenetic period,when the stationary front formed over the Korean peninsula; （3） the quasi-stationary period,when the convective band remained over Seoul for 3 h; （4） the mature period,when the cloud cover was largest and the precipitation rate was greater than 90 mm h-1; and （5） the dissipating period,when the MCB diminished and disappeared.The synoptic,thermodynamic,and dynamic analyses show that the MCB maintained its longevity by a tilted updraft,which headed towards a positive PV anomaly.Precipitation was concentrated under this area,where a tilted ascending southwesterly converged with a tilted ascending northeasterly,at the axis of cyclonic rotation.The formation of the convective cell was attributed in part by tropopause folding,which enhanced the cyclonic vorticity at the surface,and by the low-level convergence of warm moist air and upperlevel divergence.The southwesterly flow ascended in a region with high moisture content and strong relative vorticity that maintained the development of an MCB along the quasi-stationary front.
文摘Erratum to:Lee,Y.-H.,G.Lee,S.Joo,and K.-D.Ahn,2018:Observational study of surface wind along a sloping surface over mountainous terrain during winter.Adv.Atmos.Sci.,35(3),276−284,https://doi.org/10.1007/s00376-017-7075-5.
文摘Tree-ring based temperature reconstructions have successfully inferred the past inter-annual to millennium scales summer temperature variability. A clear relationship between annual and summer temperatures can provide insights into tile variability of past annual mean tem- perature from the reconstructed summer temperature. However, how similar are summer and annual temperatures is to a large extent still unknown. This study aims at investigating the relationship between annual and summer temperatures at different timescales in central Sweden during the last millennium. The temperature variability in central Sweden can represent large parts of Scandinavia which has been a key region for dendroclimatological research. The observed annual and summer temperatures during 1901-2005 were firstly decomposed into different frequency bands using ensemble empirical mode decomposition （EEMD） method, and then the scale-dependent relationship was quantified using Pearson correlation coefficients. The relationship between the observed annual and summer temperatures determined by the instrumental data was subsequently used to evaluate 7 climate models. The model with the best performance was used to infer the relationship for the last millennium. The results show that the relationship between the observed annual and summer temperatures becomes stronger as the timescale increases, except for the 4--16 years timescales at which it does not show any relationship. The summer temperature variability at short timescales （2--4 years） shows much higher variance than the annual variability, while the annual temperature variability at long timescales （〉32 years） has a much higher variance than the summer one. During the last millennium, the simulated summer temperature also shows higher variance at the short timescales （2-4 years） and lower variance at the long timescales （〉1024 years） than those of the annual temperature. The relationship between the two temperatures is generally close at the long timescales, and weak at the short timescales. Overall the summer temperature variability cannot well reflect the annual mean temperature variability for the study region during both the 20th century and the last millennium. Furthermore, all the climate models examined overestimate the annual mean temperature variance at the 2--4 years timescales, which indicates that the overestimate could be one of reasons why the volcanic eruption induced cooling is larger in climate models than in proxy data.
文摘This paper introduces a new approach for the initialization of ensemble numerical forecasting： Dynamic Analogue Initialization （DAI）. DAI assumes that the best model state trajectories for the past provide the initial conditions for the best forecasts in the future. As such, DAI performs the ensemble forecast using the best analogues from a full size ensemble. As a pilot study, the Lorenz63 and Lorenz96 models were used to test DAI＇s effectiveness independently. Results showed that DAI can improve the forecast significantly. Especially in lower-dimensional systems, DAI can reduce the forecast RMSE by ~50% compared to the Monte Carlo forecast （MC）. This improvement is because DAI is able to recognize the direction of the analysis error through the embedding process and therefore selects those good trajectories with reduced initial error. Meanwhile, a potential improvement of DAI is also proposed, and that is to find the optimal range of embedding time based on the error＇s growing speed.
基金supported by the APEC Climate Centersupported by the UNIST research fund (Grant No. 1.09006.01)provided by a grant (Grant No. 14AWMP-B082564-01) from the Advanced Water Management Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government
文摘Using 32 CMIP5（Coupled Model Intercomparison Project Phase 5） models, this study examines the veracity in the simulation of cloud amount and their radiative effects（CREs） in the historical run driven by observed external radiative forcing for 1850-2005, and their future changes in the RCP（Representative Concentration Pathway） 4.5 scenario runs for2006-2100. Validation metrics for the historical run are designed to examine the accuracy in the representation of spatial patterns for climatological mean, and annual and interannual variations of clouds and CREs. The models show large spread in the simulation of cloud amounts, specifically in the low cloud amount. The observed relationship between cloud amount and the controlling large-scale environment are also reproduced diversely by various models. Based on the validation metrics,four models-ACCESS1.0, ACCESS1.3, Had GEM2-CC, and Had GEM2-ES-are selected as best models, and the average of the four models performs more skillfully than the multimodel ensemble average.All models project global-mean SST warming at the increase of the greenhouse gases, but the magnitude varies across the simulations between 1 and 2 K, which is largely attributable to the difference in the change of cloud amount and distribution. The models that simulate more SST warming show a greater increase in the net CRE due to reduced low cloud and increased incoming shortwave radiation, particularly over the regions of marine boundary layer in the subtropics. Selected best-performing models project a significant reduction in global-mean cloud amount of about-0.99% K^-1and net radiative warming of 0.46 W m^-2K^-1, suggesting a role of positive feedback to global warming.
基金funded by the National Natural Science Foundation of China (Grant No.41676088)the National Key Research and Development Project of China (2016YFC1401800,2017YFC1404100,2017YFC1404102)+1 种基金the Fundamental Research Funds for the Central Universities (HEUCF 041705)the Foundation of the Key Laboratory of Marine Environmental Information Technology
文摘That a model has sensitivity responses to parameter uncertainties is a key concept in implementing model parameter es- timation using filtering theory and methodology. Depending on the nature of associated physics and characteristic variability of the fluid in a coupled system, the response time scales of a model to parameters can be different, from hourly to decadal. Unlike state estimation, where the update frequency is usually linked with observational frequency, the update frequency for parameter estimation must be associated with the time scale of the model sensitivity response to the parameter being esti- mated. Here, with a simple coupled model, the impact of model sensitivity response time scales on coupled model parameter estimation is studied. The model includes characteristic synoptic to decadal scales by coupling a long-term varying deep ocean with a slow-varying upper ocean forced by a chaotic atmosphere. Results show that, using the update frequency deter- mined by the model sensitivity response time scale, both the reliability and quality of parameter estimation can be improved significantly, and thus the estimated parameters make the model more consistent with the observation. These simple model results provide a guideline for when real observations are used to optimize the parameters in a coupled general circulation model for improving climate analysis and prediction initialization.
基金Supported by the National Key Basic Research Program (Grant No. 2005CB422004)the National Natural Science Foundation of China (Grant No. 40571036)+1 种基金the Cen-tury Program of CAS (Grant No. 2004401)the Talent Program of CAREERI, CAS
文摘The exchange of energy and water between the lithosphere and atmosphere mainly takes place at the ground surface. Therefore, freeze/thaw condition at the ground surface is an important factor in ex- amining the interactions between the land surface and atmosphere. Based on the observation data obtained by CEOP/CAMP-Tibet, the diurnal freeze/thaw cycles of the ground surface near Naqu, central Tibetan Plateau was preliminarily analyzed. The results show that the surface layer was completely frozen for approximately one month. However, the time that the ground surface experienced diurnal freeze/thaw cycles was about 6 months. The high frequency of freeze/thaw cycles at the ground surface significantly influences water and energy exchanges between ground and atmosphere over half a year. The interaction processes between the ground and atmosphere under different soil conditions (such as complete thaw, complete freeze and diurnal freeze/thaw cycles) are issues worthy of further examina- tion.
基金Special publicsector research of CMA,China(GYHY200906016)Innovation Plan for Graduate Students in the Universities of Jiangsu Province,China(CX07B_043z),NUIST(Y602)
文摘Based on transient simulation of the last deglaciation(significant global warming period)using a fully coupled model and sensitivity experiment,we show explicitly how the thermohaline circulation(THC)affects the climate of China,especially during periods of abrupt climate change.The simulated evolution of the Chinese climate was consistent with the paleoclimate record during the last deglaciation.For example,the whole Chinese region warmed significantly during the BФlling-AllerФd warming event(BA).When the magnitude of the THC was reduced in the sensitivity experiment during BA,warming of the Chinese region was greatly affected.Our work shows that in addition to orbital forcing and greenhouse gases,the THC is an important factor influencing climate change in China at the century scale.
基金supported by National Basic Research Program of China(Grant No. 2012CB955200)National Natural Science Foundation of China(Grant Nos.41130105,40776017)+2 种基金Open Project of KLME,NUIST(Grant No. LLME0507)Special Public Sector Research of CMA,China(Grant No. GYHY200906016)a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Atlantic thermohaline circulation(THC) is a key component of the Earth Climate System and identification of its changes during the 20th Century is critical to the understanding of its variation characteristics and the corresponding climatic impacts.Previous researches have been inconclusive,with the results varying depending on the approach used to measure THC.The results for the two established approaches for measurement of the phenomenon(direct observation and indirect reconstruction) are contradictive(weakening and non-weakening),and their credibility needs improving.Based on the tight relationship between THC anomaly and "see-saw" intensities of Sea Surface Temperature(SST) and Surface Air Temperature(SAT),we first diagnose their quantitative relationship in the model experiments,which is corresponding to its two possible scenarios,and then reconstruct the changes of THC during the 20th Century respectively with multiple observed datasets of SST and SAT.Model results show that THC anomaly and SST/SAT "see-saw" intensities are well correlated in timescales longer than 10/40 years under scenarios of weakening/non-weakening respectively.Two kinds of reconstructions here are consistent with each other,and we propose that THC has undergone a 2-cycle oscillation with inter-decadal scale since the Industrial Revolution with a magnitude of about 1 Sv.The transformation times of decadal trend are around the mid-1910s,the 1940s,and the mid-1970s.This research further validates the main results of previous reconstructions,and points out that THC does not have a long-term weakening during the 20th Century.
