Drought is a recurring dry condition with below-normal precipitation and is often associated with warm temperatures or heatwaves. A drought event can develop slowly over several weeks or suddenly within days, commonly...Drought is a recurring dry condition with below-normal precipitation and is often associated with warm temperatures or heatwaves. A drought event can develop slowly over several weeks or suddenly within days, commonly under abnormal atmospheric conditions(e.g., quasi-stationary high-pressure systems), and can persist for weeks, months, or even years.展开更多
Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many cities.How to make accurate climate predictions of extreme cold events is sti...Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many cities.How to make accurate climate predictions of extreme cold events is still an urgent issue.The synergistic effect of the warm Arctic and cold tropical Pacific has been demonstrated to intensify the intrusions of cold air from polar regions into middle-high latitudes,further influencing the cold conditions in China.However,climate models failed to predict these two ocean environments at expected lead times.Most seasonal climate forecasts only predicted the 2020/21 La Niña after the signal had already become apparent and significantly underestimated the observed Arctic sea ice loss in autumn 2020 with a 1-2 month advancement.In this work,the corresponding physical factors that may help improve the accuracy of seasonal climate predictions are further explored.For the 2020/21 La Niña prediction,through sensitivity experiments involving different atmospheric-oceanic initial conditions,the predominant southeasterly wind anomalies over the equatorial Pacific in spring of 2020 are diagnosed to play an irreplaceable role in triggering this cold event.A reasonable inclusion of atmospheric surface winds into the initialization will help the model predict La Niña development from the early spring of 2020.For predicting the Arctic sea ice loss in autumn 2020,an anomalously cyclonic circulation from the central Arctic Ocean predicted by the model,which swept abnormally hot air over Siberia into the Arctic Ocean,is recognized as an important contributor to successfully predicting the minimum Arctic sea ice extent.展开更多
On 15 September 2020,the Arctic sea-ice extent(SIE)reached its annual minimum,which,based on data from the National Snow and Ice Data Center(NSIDC,2020a),was about 3.74 million km^(2)(1.44 million square miles).This v...On 15 September 2020,the Arctic sea-ice extent(SIE)reached its annual minimum,which,based on data from the National Snow and Ice Data Center(NSIDC,2020a),was about 3.74 million km^(2)(1.44 million square miles).This value was about 40%less than the climate average(~6.27 million km^(2))during 1980–2010.It was second only to the record low(3.34 million km^(2))set on 16 September 2012,but significantly smaller than the previous second-lowest(4.145 million km^(2),set on 7 September 2016)and third-lowest(4.147 million km^(2),set on 14 September 2007)values,making 2020 the second-lowest SIE year of the satellite era(42 years of data).展开更多
The establishment of the upper-level South Asian high (SAH) over the Indo-China Peninsula (ICP) during late boreal spring and its possible causes are investigated using long-term NCEP-NCAR and ERA-40 reanalysis an...The establishment of the upper-level South Asian high (SAH) over the Indo-China Peninsula (ICP) during late boreal spring and its possible causes are investigated using long-term NCEP-NCAR and ERA-40 reanalysis and satellite-observed OLR data. Results show that, from early March to mid-April, deep convection stays south of -6°N over the northern Sumatran islands. As the maximum solar radiation moves over the latitudes of the ICP (10-20°N) in late April, the air over the ICP becomes unstable. It ascends over the ICP and descends over the adjacent waters to the east and west. This triggers deep convection over the ICP that induces large latent heating and strong updrafts and upper-level divergence, leading to the formation of an upper-level anticyclonic circulation and the SAH over the ICE During early to mid-May, deep convection over the ICP intensifies and extends northwards to the adjacent waters. Strong latent heating from deep convection enhances and maintains the strong updrafts and upper-level divergence, and the SAH is fully established by mid-May. Thus, the seasonal maximum solar heating and the land-sea contrast around the ICP provide the basic conditions for deep convection to occur preferentially over the ICP, which leads to the formation of the SAH over the ICP from late April to mid-May. Simulations using RegCM4 also indicate that the diabatic heating over the ICP is conducive to the generation and development of upper-level anticyclonic circulation, which leads to an earlier establishment of the SAH.展开更多
Dominant statistical patterns of winter Arctic surface wind (WASW) variability and their impacts on Arctic sea ice motion are investigated using the complex vector empirical orthogonal function (CVEOF) method. The...Dominant statistical patterns of winter Arctic surface wind (WASW) variability and their impacts on Arctic sea ice motion are investigated using the complex vector empirical orthogonal function (CVEOF) method. The results indicate that the leading CVEOF of Arctic surface wind variability, which accounts for 33% of the covariance, is characterized by two different and alternating spatial patterns (WASWP1 and WASWP2). Both WASWP1 and WASWP2 show strong interannual and decadal variations, superposed on their declining trends over past decades. Atmospheric circulation anomalies associated with WASWPI and WASWP2 exhibit, respectively, equivalent barotropic and some baroclinic characteristics, differing from the Arctic dipole anomaly and the seesaw structure anomaly between the Barents Sea and the Beaufort Sea. On decadal time scales, the decline trend of WASWP2 can be attributed to persistent warming of sea surface temperature in the Greenland--Barents--Kara seas from autunm to winter, reflecting the effect of the Arctic warming. The second CVEOF, which accounts for 18% of the covariance, also contains two different spatial patterns (WASWP3 and WASWP4). Their time evolutions are significantly correlated with the North Atlantic Oscillation (NAO) index and the central Arctic Pattern, respectively, measured by the leading EOF of winter sea level pressure (SLP) north of 70~N. Thus, winter anomalous surface wind pattern associated with the NAO is not the most important surface wind pattern. WASWP3 and WASWP4 primarily reflect natural variability of winter surface wind and neither exhibits an apparent trend that differs from WASWP1 or WASWP2. These dominant surface wind patterns strongly influence Arctic sea ice motion and sea ice exchange between the western and eastern Arctic. Furthermore, the Fram Strait sea ice volume flux is only significantly correlated with WASWP3. The results demonstrate that surface and geostrophic winds are not interchangeable in terms of describing wind field variability over the Arctic Ocean. The results have important implications for understanding and investigating Arctic sea ice variations: Dominant patterns of Arctic surface wind variability, rather than simply whether there are the Arctic dipole anomaly and the Arctic Oscillation (or NAO), effectively affect the spatial distribution of Arctic sea ice anomalies.展开更多
In this study,we perform a stand-alone sensitivity study using the Los Alamos Sea ice model version 6(CICE6)to investigate the model sensitivity to two Ice-Ocean(IO)boundary condition approaches.One is the two-equatio...In this study,we perform a stand-alone sensitivity study using the Los Alamos Sea ice model version 6(CICE6)to investigate the model sensitivity to two Ice-Ocean(IO)boundary condition approaches.One is the two-equation approach that treats the freezing temperature as a function of the ocean mixed layer(ML)salinity,using two equations to parametrize the IO heat exchanges.Another approach uses the salinity of the IO interface to define the actual freezing temperature,so an equation describing the salt flux at the IO interface is added to the two-equation approach,forming the so-called three-equation approach.We focus on the impact of the three-equation boundary condition on the IO heat exchange and associated basal melt/growth of the sea ice in the Arctic Ocean.Compared with the two-equation simulation,our three-equation simulation shows a reduced oceanic turbulent heat flux,weakened basal melt,increased ice thickness,and reduced sea surface temperature(SST)in the Arctic.These impacts occur mainly at the ice edge regions and manifest themselves in summer.Furthermore,in August,we observed a downward turbulent heat flux from the ice to the ocean ML in two of our three-equation sensitivity runs with a constant heat transfer coefficient(0.006),which caused heat divergence and congelation at the ice bottom.Additionally,the influence of different combinations of heat/salt transfer coefficients and thermal conductivity in the three-equation approach on the model simulated results is assessed.The results presented in this study can provide insight into sea ice model sensitivity to the three-equation IO boundary condition for coupling the CICE6 to climate models.展开更多
To improve the Arctic sea ice forecast skill of the First Institute of Oceanography-Earth System Model(FIO-ESM)climate forecast system,satellite-derived sea ice concentration and sea ice thickness from the Pan-Arctic ...To improve the Arctic sea ice forecast skill of the First Institute of Oceanography-Earth System Model(FIO-ESM)climate forecast system,satellite-derived sea ice concentration and sea ice thickness from the Pan-Arctic IceOcean Modeling and Assimilation System(PIOMAS)are assimilated into this system,using the method of localized error subspace transform ensemble Kalman filter(LESTKF).Five-year(2014–2018)Arctic sea ice assimilation experiments and a 2-month near-real-time forecast in August 2018 were conducted to study the roles of ice data assimilation.Assimilation experiment results show that ice concentration assimilation can help to get better modeled ice concentration and ice extent.All the biases of ice concentration,ice cover,ice volume,and ice thickness can be reduced dramatically through ice concentration and thickness assimilation.The near-real-time forecast results indicate that ice data assimilation can improve the forecast skill significantly in the FIO-ESM climate forecast system.The forecasted Arctic integrated ice edge error is reduced by around 1/3 by sea ice data assimilation.Compared with the six near-real-time Arctic sea ice forecast results from the subseasonal-toseasonal(S2 S)Prediction Project,FIO-ESM climate forecast system with LESTKF ice data assimilation has relatively high Arctic sea ice forecast skill in 2018 summer sea ice forecast.Since sea ice thickness in the PIOMAS is updated in time,it is a good choice for data assimilation to improve sea ice prediction skills in the near-realtime Arctic sea ice seasonal prediction.展开更多
1 Background and purpose of workshop The Southern Ocean plays a fundamental role in the function of the Earth System, influencing climate, sea level, biogeochemical cycles, and biological productivity on a variety of ...1 Background and purpose of workshop The Southern Ocean plays a fundamental role in the function of the Earth System, influencing climate, sea level, biogeochemical cycles, and biological productivity on a variety of scalesIll. Observations from the Southern Ocean suggest that dramatic changes are taking place, which are of global concern, yet because of its remote location, seasonal sea ice, and harsh environment, the Southern Ocean remains one of the least sampled zones in the world.展开更多
Snow depth over sea ice is an essential variable for understanding the Arctic energy budget.In this study,we evaluate snow depth over Arctic sea ice during 1993-2014 simulated by 31 models from phase 6 of the Coupled ...Snow depth over sea ice is an essential variable for understanding the Arctic energy budget.In this study,we evaluate snow depth over Arctic sea ice during 1993-2014 simulated by 31 models from phase 6 of the Coupled Model Intercomparison Project(CMIP6)against recent satellite retrievals.The CMIP6 models capture some aspects of the observed snow depth climatology and variability.The observed variability lies in the middle of the models’simulations.All the models show negative trends of snow depth during 1993-2014.However,substantial spatiotemporal discrepancies are identified.Compared to the observation,most models have late seasonal maximum snow depth(by two months),remarkably thinner snow for the seasonal minimum,an incorrect transition from the growth to decay period,and a greatly underestimated interannual variability and thinning trend of snow depth over areas with frequent occurrence of multi-year sea ice.Most models are unable to reproduce the observed snow depth gradient from the Canadian Arctic to the outer areas and the largest thinning rate in the central Arctic.Future projections suggest that snow depth in the Arctic will continue to decrease from 2015 to 2099.Under the SSP5-8.5 scenario,the Arctic will be almost snow-free during the summer and fall and the accumulation of snow starts from January.Further investigation into the possible causes of the issues for the simulated snow depth by some models based on the same family of models suggests that resolution,the inclusion of a hightop atmospheric model,and biogeochemistry processes are important factors for snow depth simulation.展开更多
Tropical cyclone (TC) causes huge damage to lives and properties due to strong winds,storm surge,heavy rainfall and flooding(Peduzzi et al.,2012;Zhang et al.,2009).Climate model simulations suggested that the frequenc...Tropical cyclone (TC) causes huge damage to lives and properties due to strong winds,storm surge,heavy rainfall and flooding(Peduzzi et al.,2012;Zhang et al.,2009).Climate model simulations suggested that the frequency of TCs might increase during the 21st century,especially over the western North Pacific (Emanuel,2013).Climate changes tend to double the economic damages caused by natural disaster,i.e.,strong TCs.East Asia hit by TCs may suffer great damages in the future (Mendelsohn et al.,2012).展开更多
The Antarctic,including the continent of Antarctica and the Southern Ocean,is a critically important part of the Earth system.Research in Antarctic meteorology and climate has always been a challenging endeavor.Studyi...The Antarctic,including the continent of Antarctica and the Southern Ocean,is a critically important part of the Earth system.Research in Antarctic meteorology and climate has always been a challenging endeavor.Studying and predicting weather patterns in the Antarctic are important for understanding their role in local-to-global processes and facilitating field studies and logistical operations in the Antarctic(e.g.,Walsh et al.,2018).Studies of climate change in the Antarctic are comparatively neglected compared to those of the Arctic.However,significant climate changes have occurred in the Antarctic in the past several decades,i.e.,a strong warming over the Antarctic Peninsula even with a recent minor cooling,a deepening of the Amundsen Sea low,a rapid warming of the upper ocean north of the circumpolar current,an increase of Antarctic sea ice since the late 1970s followed by a recent rapid decrease,and an accelerated ice loss from the Antarctic ice shelf/sheet since the late 1970s(e.g.,Turner et al.,2005;Raphael et al.,2016;Sallée,2018;Parkinson,2019;Rignot et al.,2019).Investigating recent climate change in the Antarctic and the underlying mechanisms are important for predicting future climate change and providing information to policymakers.展开更多
Our knowledge about the interaction between human activities and the environment in the middle-late Holocene remains incomplete.Core C1 in Lake Chaohu from the middle and lower reaches of Yangtze River (MLYR),eastern ...Our knowledge about the interaction between human activities and the environment in the middle-late Holocene remains incomplete.Core C1 in Lake Chaohu from the middle and lower reaches of Yangtze River (MLYR),eastern China,provides an opportunity to investigate vegetation and climate changes,human activities,and East Asian summer monsoon(EASM) evolution since 5100 cal.yr BP.These variables are assessed based on radiocarbon dating,pollen and charcoal records,and magnetic susceptibility (χ_(lf)),median grain size and TP.Results reveal a hiatus in sedimentation between 2080 and 730 cal.yr BP in the western part of Lake Chaohu,which is common in most lakes in the MLYR.Evergreen and deciduous broadleaved mixed forest retreated gradually after 3650 cal.yr BP,and was replaced by secondary Pinus forest after at least 730 cal.yr BP.Intense agricultural activities and vegetation clearance are first detected at 2520 cal.yr BP.Human settlements expanded from the lake front wetlands (during the period 2520–2080 cal.yr BP) to remote high-altitude areas(2080–400 cal.yr BP),and then returned to the lake front to reclaim the wetlands and lake (after 400 cal.yr BP).A gradual trend of recessional EASM strength from 4300 cal.yr BP and centennial-scale variations of EASM during the period5100–3650 cal.yr BP are revealed.The reduction of summer insolation,southward shift of the ITCZ,and El Ni?o Southern Oscillation may control the intensity of EASM and climate on a large regional scale.展开更多
Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice.While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused...Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice.While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused by stratospheric ozone changes,here we show that stratospheric ozone-induced cloud radiative effects also play important roles in causing changes in Antarctic sea ice.Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes decreases in clouds over Southern Hemisphere(SH)high latitudes and increases in clouds over the SH extratropics.The decrease in clouds leads to a reduction in downward infrared radiation,especially in austral autumn.This results in cooling of the Southern Ocean surface and increasing Antarctic sea ice.Surface cooling also involves ice-albedo feedback.Increasing sea ice reflects solar radiation and causes further cooling and more increases in Antarctic sea ice.展开更多
The first Southern Ocean Observing System (SOOS) Asian Workshop was successfully held in Shanghai, China in May 2013, attracting over 40 participants from six Asian nations and widening exposure to the objectives an...The first Southern Ocean Observing System (SOOS) Asian Workshop was successfully held in Shanghai, China in May 2013, attracting over 40 participants from six Asian nations and widening exposure to the objectives and plans of SOOS. The workshop was organized to clarify Asian research activities currently taking place in the Southern Ocean and to discuss, amongst other items, the potential for collaborative efforts with and between Asian countries in $OOS-related activities. The workshop was an important mechanism to initiate discussion, understanding and collaborative avenues in the Asian domain of SOOS beyond current established eflbrts. Here we present some of the major outcomes of the workshop covering the principle themes of SOOS and attempt to provide a way forward to achieve a more integrated research community, enhance data collection and quality, and guide scientific strategy in the Southern Ocean.展开更多
Due to the shortage of the global observational data of the terrestrial hydrological variables,the understanding of how surface hydrological processes respond to climate change is still limited.In this study,the Commu...Due to the shortage of the global observational data of the terrestrial hydrological variables,the understanding of how surface hydrological processes respond to climate change is still limited.In this study,the Community Land Model(CLM4.0)with high resolution atmospheric forcing data is selected to simulate the global surface hydrological quantities during the period 1948–2006and to investigate the spatial features of these quantities in response to climate change at the regional scales.The sensitivities of evaporation and runoff with respect to the dominant climate change factors(e.g.temperature and precipitation)derived from the concept of climate elasticity are introduced.Results show that evaporation has a declining trend with a rate of 0.7 mm per decade,while runoff shows a weak increasing trend of 0.15 mm per decade over the global land surface.Analyses of the hotspots in the hydrological cycle indicate that the spatial distributions for evaporation and runoff are similar over many areas in central Asia,Australia,and southern South America,but differ largely in high latitudes.It is also found that,the evaporation hotspots in arid regions are mainly associated with the changes in precipitation.Our sensitive analysis suggests that the hydrological quantities show a rather complicated spatial dependency of response of the water cycle to the different climate factors(temperature and precipitation).展开更多
Air quality in eastern China has becoming more and more worrying in recent years, and haze is now No.1 air pollution issue. Results in this study show the decreasing Arctic sea ice(ASI) is an important contributor to ...Air quality in eastern China has becoming more and more worrying in recent years, and haze is now No.1 air pollution issue. Results in this study show the decreasing Arctic sea ice(ASI) is an important contributor to the recent increased haze days in eastern China. The authors find that the number of winter haze days(WHD) in eastern China is strongly negatively correlated with the preceding autumn ASI during 1979–2012, and about 45%– 67% of the WHD interannual to interdecadal variability can be explained by ASI variability. Following previous studies on the impact of ASI loss on the northern hemisphere climate, the authors' studies further reveal that the reduction of autumn ASI leads to positive sea-level pressure anomalies in mid-latitude Eurasia, northward shift of track of cyclone activity in China, and weak Rossby wave activity in eastern China south of 40N during winter season. These atmospheric circulation changes favor less cyclone activity and more stable atmosphere in eastern China, leading to more haze days there. Furthermore, the patterns of circulation changes associated with autumn ASI and WHD are in very good agreement over the East Asia, particularly in eastern China. The authors suggest that haze pollution may continue to be a serious issue in the near future as the decline of ASI continues under global warming.展开更多
文摘Drought is a recurring dry condition with below-normal precipitation and is often associated with warm temperatures or heatwaves. A drought event can develop slowly over several weeks or suddenly within days, commonly under abnormal atmospheric conditions(e.g., quasi-stationary high-pressure systems), and can persist for weeks, months, or even years.
基金supported by the Key Research Program of Frontier Sciences,CAS (Grant No. ZDBS-LY-DQC010)the National Natural Science Foundation of China (Grant Nos. 41876012 and 41861144015,42175045)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB42000000).
文摘Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many cities.How to make accurate climate predictions of extreme cold events is still an urgent issue.The synergistic effect of the warm Arctic and cold tropical Pacific has been demonstrated to intensify the intrusions of cold air from polar regions into middle-high latitudes,further influencing the cold conditions in China.However,climate models failed to predict these two ocean environments at expected lead times.Most seasonal climate forecasts only predicted the 2020/21 La Niña after the signal had already become apparent and significantly underestimated the observed Arctic sea ice loss in autumn 2020 with a 1-2 month advancement.In this work,the corresponding physical factors that may help improve the accuracy of seasonal climate predictions are further explored.For the 2020/21 La Niña prediction,through sensitivity experiments involving different atmospheric-oceanic initial conditions,the predominant southeasterly wind anomalies over the equatorial Pacific in spring of 2020 are diagnosed to play an irreplaceable role in triggering this cold event.A reasonable inclusion of atmospheric surface winds into the initialization will help the model predict La Niña development from the early spring of 2020.For predicting the Arctic sea ice loss in autumn 2020,an anomalously cyclonic circulation from the central Arctic Ocean predicted by the model,which swept abnormally hot air over Siberia into the Arctic Ocean,is recognized as an important contributor to successfully predicting the minimum Arctic sea ice extent.
基金This work was supported by the National Key R&D Program of China[grant number 2018YFA0605901]the National Natural Science Foundation of China[grant numbers 41861144016 and 42011530082].
文摘On 15 September 2020,the Arctic sea-ice extent(SIE)reached its annual minimum,which,based on data from the National Snow and Ice Data Center(NSIDC,2020a),was about 3.74 million km^(2)(1.44 million square miles).This value was about 40%less than the climate average(~6.27 million km^(2))during 1980–2010.It was second only to the record low(3.34 million km^(2))set on 16 September 2012,but significantly smaller than the previous second-lowest(4.145 million km^(2),set on 7 September 2016)and third-lowest(4.147 million km^(2),set on 14 September 2007)values,making 2020 the second-lowest SIE year of the satellite era(42 years of data).
基金supported by the National Natural Science Foundation of China[grant number 41176169]the National Basic Research Program of China[grant number 2011CB309704]
基金jointly supported by the Major Program of the Natural Science Researches for Colleges and Universities in Jiangsu Province(Grant No.14KJA170004)the Natural Science Foundation of Jiangsu Province(Grant No.BK20131432)+5 种基金the“333”Project of Jiangsu Province“Qing Lan”Project of Jiangsu Provincethe Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)supported by the U.S.National Science Foundation(Grant No.AGS-1353740)the U.S.Department of Energy’s Office of Science(Grant No.DE-SC0012602)the U.S.National Oceanic and Atmospheric Administration(Grant No.NA15OAR4310086)
文摘The establishment of the upper-level South Asian high (SAH) over the Indo-China Peninsula (ICP) during late boreal spring and its possible causes are investigated using long-term NCEP-NCAR and ERA-40 reanalysis and satellite-observed OLR data. Results show that, from early March to mid-April, deep convection stays south of -6°N over the northern Sumatran islands. As the maximum solar radiation moves over the latitudes of the ICP (10-20°N) in late April, the air over the ICP becomes unstable. It ascends over the ICP and descends over the adjacent waters to the east and west. This triggers deep convection over the ICP that induces large latent heating and strong updrafts and upper-level divergence, leading to the formation of an upper-level anticyclonic circulation and the SAH over the ICE During early to mid-May, deep convection over the ICP intensifies and extends northwards to the adjacent waters. Strong latent heating from deep convection enhances and maintains the strong updrafts and upper-level divergence, and the SAH is fully established by mid-May. Thus, the seasonal maximum solar heating and the land-sea contrast around the ICP provide the basic conditions for deep convection to occur preferentially over the ICP, which leads to the formation of the SAH over the ICP from late April to mid-May. Simulations using RegCM4 also indicate that the diabatic heating over the ICP is conducive to the generation and development of upper-level anticyclonic circulation, which leads to an earlier establishment of the SAH.
基金supported by the National Key Basic Research Project of China (Grant nos.2013CBA01804,2015CB453200)the National Natural Science Foundation of China (Grant nos.41475080,41221064)the Ocean Public Welfare Scientific Research Project of China (Grant no.201205007)
文摘Dominant statistical patterns of winter Arctic surface wind (WASW) variability and their impacts on Arctic sea ice motion are investigated using the complex vector empirical orthogonal function (CVEOF) method. The results indicate that the leading CVEOF of Arctic surface wind variability, which accounts for 33% of the covariance, is characterized by two different and alternating spatial patterns (WASWP1 and WASWP2). Both WASWP1 and WASWP2 show strong interannual and decadal variations, superposed on their declining trends over past decades. Atmospheric circulation anomalies associated with WASWPI and WASWP2 exhibit, respectively, equivalent barotropic and some baroclinic characteristics, differing from the Arctic dipole anomaly and the seesaw structure anomaly between the Barents Sea and the Beaufort Sea. On decadal time scales, the decline trend of WASWP2 can be attributed to persistent warming of sea surface temperature in the Greenland--Barents--Kara seas from autunm to winter, reflecting the effect of the Arctic warming. The second CVEOF, which accounts for 18% of the covariance, also contains two different spatial patterns (WASWP3 and WASWP4). Their time evolutions are significantly correlated with the North Atlantic Oscillation (NAO) index and the central Arctic Pattern, respectively, measured by the leading EOF of winter sea level pressure (SLP) north of 70~N. Thus, winter anomalous surface wind pattern associated with the NAO is not the most important surface wind pattern. WASWP3 and WASWP4 primarily reflect natural variability of winter surface wind and neither exhibits an apparent trend that differs from WASWP1 or WASWP2. These dominant surface wind patterns strongly influence Arctic sea ice motion and sea ice exchange between the western and eastern Arctic. Furthermore, the Fram Strait sea ice volume flux is only significantly correlated with WASWP3. The results demonstrate that surface and geostrophic winds are not interchangeable in terms of describing wind field variability over the Arctic Ocean. The results have important implications for understanding and investigating Arctic sea ice variations: Dominant patterns of Arctic surface wind variability, rather than simply whether there are the Arctic dipole anomaly and the Arctic Oscillation (or NAO), effectively affect the spatial distribution of Arctic sea ice anomalies.
基金the National Key R&D Program of China(Grant No.2018YFA0605901)the National Natural Science Foundation of China(Grant No.41775089)+1 种基金the National Key R&D Program of China(Grant No.2017YFC1502304)the Partnership for Education and Cooperation in Operational Oceanography(PECO_(2))project awarded by the Research Council of Norway(111280).
文摘In this study,we perform a stand-alone sensitivity study using the Los Alamos Sea ice model version 6(CICE6)to investigate the model sensitivity to two Ice-Ocean(IO)boundary condition approaches.One is the two-equation approach that treats the freezing temperature as a function of the ocean mixed layer(ML)salinity,using two equations to parametrize the IO heat exchanges.Another approach uses the salinity of the IO interface to define the actual freezing temperature,so an equation describing the salt flux at the IO interface is added to the two-equation approach,forming the so-called three-equation approach.We focus on the impact of the three-equation boundary condition on the IO heat exchange and associated basal melt/growth of the sea ice in the Arctic Ocean.Compared with the two-equation simulation,our three-equation simulation shows a reduced oceanic turbulent heat flux,weakened basal melt,increased ice thickness,and reduced sea surface temperature(SST)in the Arctic.These impacts occur mainly at the ice edge regions and manifest themselves in summer.Furthermore,in August,we observed a downward turbulent heat flux from the ice to the ocean ML in two of our three-equation sensitivity runs with a constant heat transfer coefficient(0.006),which caused heat divergence and congelation at the ice bottom.Additionally,the influence of different combinations of heat/salt transfer coefficients and thermal conductivity in the three-equation approach on the model simulated results is assessed.The results presented in this study can provide insight into sea ice model sensitivity to the three-equation IO boundary condition for coupling the CICE6 to climate models.
基金The National Key Research and Development Program of China under contract Nos 2018YFC1407205 and2018YFA0605901the Basic Scientific Fund for National Public Research Institute of China(ShuXingbei Young Talent Program)under contract No.2019S06+1 种基金the National Natural Science Foundation of China under contract Nos 41821004,42022042 and 41941012the China-Korea Cooperation Project on Northwestern Pacific Climate Change and its Prediction。
文摘To improve the Arctic sea ice forecast skill of the First Institute of Oceanography-Earth System Model(FIO-ESM)climate forecast system,satellite-derived sea ice concentration and sea ice thickness from the Pan-Arctic IceOcean Modeling and Assimilation System(PIOMAS)are assimilated into this system,using the method of localized error subspace transform ensemble Kalman filter(LESTKF).Five-year(2014–2018)Arctic sea ice assimilation experiments and a 2-month near-real-time forecast in August 2018 were conducted to study the roles of ice data assimilation.Assimilation experiment results show that ice concentration assimilation can help to get better modeled ice concentration and ice extent.All the biases of ice concentration,ice cover,ice volume,and ice thickness can be reduced dramatically through ice concentration and thickness assimilation.The near-real-time forecast results indicate that ice data assimilation can improve the forecast skill significantly in the FIO-ESM climate forecast system.The forecasted Arctic integrated ice edge error is reduced by around 1/3 by sea ice data assimilation.Compared with the six near-real-time Arctic sea ice forecast results from the subseasonal-toseasonal(S2 S)Prediction Project,FIO-ESM climate forecast system with LESTKF ice data assimilation has relatively high Arctic sea ice forecast skill in 2018 summer sea ice forecast.Since sea ice thickness in the PIOMAS is updated in time,it is a good choice for data assimilation to improve sea ice prediction skills in the near-realtime Arctic sea ice seasonal prediction.
基金hosted and sponsored by the Polar Research Institute of China (PRIC), with additional sponsorship by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP/CAS), the World Climate Research Programme (WCRP) "Climate and the Cryosphere" project (CliC), the Scientific Committee on Antarctic Research (SCAR), and the Scientific Committee on Oceanic Research (SCOR). SOOS acknowledges the support of its host institute, the Institute for Marine and Antarctic Studies (IMAS, University of Tasmania, Australia), and sponsors, Australian Antarctic Division, Antarctica New Zealand, and the New Zealand Antarctic Research Institute.
文摘1 Background and purpose of workshop The Southern Ocean plays a fundamental role in the function of the Earth System, influencing climate, sea level, biogeochemical cycles, and biological productivity on a variety of scalesIll. Observations from the Southern Ocean suggest that dramatic changes are taking place, which are of global concern, yet because of its remote location, seasonal sea ice, and harsh environment, the Southern Ocean remains one of the least sampled zones in the world.
基金supported by the NOAA Climate Program Office(Grant No.NA15OAR4310163)the National Key R&D Program of China(Grant Nos.2018YFA0605904 and 2018YFA0605901)the National Natural Science Foundation of China(Grant No.41676185)。
文摘Snow depth over sea ice is an essential variable for understanding the Arctic energy budget.In this study,we evaluate snow depth over Arctic sea ice during 1993-2014 simulated by 31 models from phase 6 of the Coupled Model Intercomparison Project(CMIP6)against recent satellite retrievals.The CMIP6 models capture some aspects of the observed snow depth climatology and variability.The observed variability lies in the middle of the models’simulations.All the models show negative trends of snow depth during 1993-2014.However,substantial spatiotemporal discrepancies are identified.Compared to the observation,most models have late seasonal maximum snow depth(by two months),remarkably thinner snow for the seasonal minimum,an incorrect transition from the growth to decay period,and a greatly underestimated interannual variability and thinning trend of snow depth over areas with frequent occurrence of multi-year sea ice.Most models are unable to reproduce the observed snow depth gradient from the Canadian Arctic to the outer areas and the largest thinning rate in the central Arctic.Future projections suggest that snow depth in the Arctic will continue to decrease from 2015 to 2099.Under the SSP5-8.5 scenario,the Arctic will be almost snow-free during the summer and fall and the accumulation of snow starts from January.Further investigation into the possible causes of the issues for the simulated snow depth by some models based on the same family of models suggests that resolution,the inclusion of a hightop atmospheric model,and biogeochemistry processes are important factors for snow depth simulation.
基金The National Key R&D Program of China under contract No.2018YFA0605901the National Natural Science Foundation of China under contract No.41676185the Joint PhD Program of China Scholarship Council(CSC)。
文摘Tropical cyclone (TC) causes huge damage to lives and properties due to strong winds,storm surge,heavy rainfall and flooding(Peduzzi et al.,2012;Zhang et al.,2009).Climate model simulations suggested that the frequency of TCs might increase during the 21st century,especially over the western North Pacific (Emanuel,2013).Climate changes tend to double the economic damages caused by natural disaster,i.e.,strong TCs.East Asia hit by TCs may suffer great damages in the future (Mendelsohn et al.,2012).
基金the National Key R&D Program of China(Grant No.2018YFA0605901).
文摘The Antarctic,including the continent of Antarctica and the Southern Ocean,is a critically important part of the Earth system.Research in Antarctic meteorology and climate has always been a challenging endeavor.Studying and predicting weather patterns in the Antarctic are important for understanding their role in local-to-global processes and facilitating field studies and logistical operations in the Antarctic(e.g.,Walsh et al.,2018).Studies of climate change in the Antarctic are comparatively neglected compared to those of the Arctic.However,significant climate changes have occurred in the Antarctic in the past several decades,i.e.,a strong warming over the Antarctic Peninsula even with a recent minor cooling,a deepening of the Amundsen Sea low,a rapid warming of the upper ocean north of the circumpolar current,an increase of Antarctic sea ice since the late 1970s followed by a recent rapid decrease,and an accelerated ice loss from the Antarctic ice shelf/sheet since the late 1970s(e.g.,Turner et al.,2005;Raphael et al.,2016;Sallée,2018;Parkinson,2019;Rignot et al.,2019).Investigating recent climate change in the Antarctic and the underlying mechanisms are important for predicting future climate change and providing information to policymakers.
基金supported by the National Key Research and Development Program of China (Grant No.2022YFF0801101)the National Natural Science Foundation of China (Grant Nos.42077424,41877434,42171161)。
文摘Our knowledge about the interaction between human activities and the environment in the middle-late Holocene remains incomplete.Core C1 in Lake Chaohu from the middle and lower reaches of Yangtze River (MLYR),eastern China,provides an opportunity to investigate vegetation and climate changes,human activities,and East Asian summer monsoon(EASM) evolution since 5100 cal.yr BP.These variables are assessed based on radiocarbon dating,pollen and charcoal records,and magnetic susceptibility (χ_(lf)),median grain size and TP.Results reveal a hiatus in sedimentation between 2080 and 730 cal.yr BP in the western part of Lake Chaohu,which is common in most lakes in the MLYR.Evergreen and deciduous broadleaved mixed forest retreated gradually after 3650 cal.yr BP,and was replaced by secondary Pinus forest after at least 730 cal.yr BP.Intense agricultural activities and vegetation clearance are first detected at 2520 cal.yr BP.Human settlements expanded from the lake front wetlands (during the period 2520–2080 cal.yr BP) to remote high-altitude areas(2080–400 cal.yr BP),and then returned to the lake front to reclaim the wetlands and lake (after 400 cal.yr BP).A gradual trend of recessional EASM strength from 4300 cal.yr BP and centennial-scale variations of EASM during the period5100–3650 cal.yr BP are revealed.The reduction of summer insolation,southward shift of the ITCZ,and El Ni?o Southern Oscillation may control the intensity of EASM and climate on a large regional scale.
基金the National Key R&D Program of China(2018YFA0605901)Y.XIA and Y.Y.HU are supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.41530423 and 41761144072)+4 种基金Y.XIA is supported by the China Postdoctoral Science Foundation funded project(Grant No.2018M630027)Y.HUANG is supported by the Discovery Program of the Natural Sciences and Engineering Council of Canada(Grant No.RGPIN 418305-13)the Team Research Project Program of the Fonds de RechercheNature et Technologies of Quebec(Grant No.PR-190145)J.P.LIU is supported by the Climate Observation and Earth System Science Divisions,Climate Program Office,NOAA,U.S.Department of Commerce(Grant Nos.NA15OAR4310163 and NA14OAR4310216)J.T.LIN is supported by the NSFC(Grant No.41775115)and the 973 program(Grant No.2014CB441303).
文摘Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice.While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused by stratospheric ozone changes,here we show that stratospheric ozone-induced cloud radiative effects also play important roles in causing changes in Antarctic sea ice.Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes decreases in clouds over Southern Hemisphere(SH)high latitudes and increases in clouds over the SH extratropics.The decrease in clouds leads to a reduction in downward infrared radiation,especially in austral autumn.This results in cooling of the Southern Ocean surface and increasing Antarctic sea ice.Surface cooling also involves ice-albedo feedback.Increasing sea ice reflects solar radiation and causes further cooling and more increases in Antarctic sea ice.
基金supported by the National Major Research High Performance Computing Program of China[grant number 2016YFB0200800]the National Natural Science Foundation of China[grant number 41676185]the NOAA Climate Program Office[grant number NA14OAR4310216]
基金hosted and sponsored by the Polar Research Institute of China (PRIC), with additional sponsorship by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP/CAS), the World Climate Research Programme (WCRP) "Climate and the Cryosphere" project (CliC), SCAR and the Scientific Committee on Oceanic Research (SCOR). We thank Alexander Klepikov, Hyoung Chul Shin, Katsuro Katsumata for providing the information on ship tracks. The conveners would like to thank the efforts by all participants, in particular the presenters, in making the first SOOS Asia Workshop a successful forum by which to highlight the extensive Asian research activities in the Southern Ocean and discuss a way forward in driving collaboration and integration with SOOS, as well as the greater international community. SOOS would like to recognize the support of the Institute for Marine and Antarctic Studies (IMAS, University of Tasmania) in hosting the SOOS International Project Office, and the sponsorship of the office by numerous international organizations (see www.soos.aq/index.php/ about-us/sponsors)
文摘The first Southern Ocean Observing System (SOOS) Asian Workshop was successfully held in Shanghai, China in May 2013, attracting over 40 participants from six Asian nations and widening exposure to the objectives and plans of SOOS. The workshop was organized to clarify Asian research activities currently taking place in the Southern Ocean and to discuss, amongst other items, the potential for collaborative efforts with and between Asian countries in $OOS-related activities. The workshop was an important mechanism to initiate discussion, understanding and collaborative avenues in the Asian domain of SOOS beyond current established eflbrts. Here we present some of the major outcomes of the workshop covering the principle themes of SOOS and attempt to provide a way forward to achieve a more integrated research community, enhance data collection and quality, and guide scientific strategy in the Southern Ocean.
基金supported by the Special Funds for Public Welfare of China(GYHY 201206017)the National Natural Science Foundation of China(41075082 and 41230422)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Due to the shortage of the global observational data of the terrestrial hydrological variables,the understanding of how surface hydrological processes respond to climate change is still limited.In this study,the Community Land Model(CLM4.0)with high resolution atmospheric forcing data is selected to simulate the global surface hydrological quantities during the period 1948–2006and to investigate the spatial features of these quantities in response to climate change at the regional scales.The sensitivities of evaporation and runoff with respect to the dominant climate change factors(e.g.temperature and precipitation)derived from the concept of climate elasticity are introduced.Results show that evaporation has a declining trend with a rate of 0.7 mm per decade,while runoff shows a weak increasing trend of 0.15 mm per decade over the global land surface.Analyses of the hotspots in the hydrological cycle indicate that the spatial distributions for evaporation and runoff are similar over many areas in central Asia,Australia,and southern South America,but differ largely in high latitudes.It is also found that,the evaporation hotspots in arid regions are mainly associated with the changes in precipitation.Our sensitive analysis suggests that the hydrological quantities show a rather complicated spatial dependency of response of the water cycle to the different climate factors(temperature and precipitation).
基金supported by the National Natural Science Foundation of China (Grant Nos. 41421004 and 41210007)
文摘Air quality in eastern China has becoming more and more worrying in recent years, and haze is now No.1 air pollution issue. Results in this study show the decreasing Arctic sea ice(ASI) is an important contributor to the recent increased haze days in eastern China. The authors find that the number of winter haze days(WHD) in eastern China is strongly negatively correlated with the preceding autumn ASI during 1979–2012, and about 45%– 67% of the WHD interannual to interdecadal variability can be explained by ASI variability. Following previous studies on the impact of ASI loss on the northern hemisphere climate, the authors' studies further reveal that the reduction of autumn ASI leads to positive sea-level pressure anomalies in mid-latitude Eurasia, northward shift of track of cyclone activity in China, and weak Rossby wave activity in eastern China south of 40N during winter season. These atmospheric circulation changes favor less cyclone activity and more stable atmosphere in eastern China, leading to more haze days there. Furthermore, the patterns of circulation changes associated with autumn ASI and WHD are in very good agreement over the East Asia, particularly in eastern China. The authors suggest that haze pollution may continue to be a serious issue in the near future as the decline of ASI continues under global warming.