查看更多>>摘要：The throughflow in the Canadian Arctic Archipelago (CAA) had a significant impact on the North Atlantic Ocean with the Arctic climate change.The findings of physical mechanisms driving the throughflow in the CAA differed and few studies about the impact of sea level pressure(SLP) on the CAA throughflow were made.A high-resolution ice-ocean coupled Arctic Ocean Finite-Volume Community Ocean Model (AO-FVCOM) was used over the period 1978-2016 to examine the interannual and seasonal variability of the outflows in the CAA and the mechanism of SLP in driving the variation of the CAA throughflow quantitively.The simulated volume transport through Davis Strait,Nares Strait,Lancaster Sound and Jones Sound showed consistent increasing trends over 1978-2016 and the larger flux in winter and spring than in summer and fall.The variation of volume transport through Nares Strait contributed more than Lancaster and Jones Sound to the variation through Davis Strait.Five process-oriented experiments were made to further explore the role of SLP in setting up and controlling the sea surface height (SSH) difference and thus the throughflow transport in the CAA.The SLP was a primary forcing to control the SSH difference and the outflow transport compared with the wind forcing.The memory of the SSH to the SLP was short and an equilibrium state could be reached if the SLP varied with time.The upstream and downstream SLP difference,however,made a slight direct contribution to driving the volume transport of the CAA throughflow.In addition to the external forcing of SLP and wind,the variability of the CAA outflow was also influenced by the variability of the inflow/outflow and SSH on boundaries connected to the Pacific and Atlantic Oceans.The choice of SLP datasets from CORE-v2,ECMWF and NCEP was sensitive to the simulated uncertainty of volume transport.
查看更多>>摘要：Whether Arctic sea-ice loss has significant impacts on climate extremes in mid-and high-latitudes remains uncertain.Here we show the full response of cold and warm extremes under two Arctic sea-ice loss scenarios utilizing a coupled global climate model that permits the air-sea coupling.Our results show that the amount of Arctic sea-ice loss determines the spatial extent and magnitude of the weakening of atmospheric circulation in mid-and high-latitudes of the northern hemisphere,leading to nonlinear changes in cold and warm extremes.A relatively localized and moderate weakening of atmospheric circulation induced by the projected sea-ice loss in the next two decades would contribute to less winter cold extremes over the Northern Hemispheric continents.The risks of winter cold spells would be dramatically reduced as the amount of sea-ice loss is increased to the ice-free state.In contrast,as sea-ice loss increases,the continental regions would have increased risk of heat waves over all mid-and high-latitudes.
查看更多>>摘要：Sea ice conditions in the Canadian Arctic Archipelago (CAA) play a key role in the navigation of the Northwest Passage (NWP).Limited by observed sea ice thickness data,the research of temporal and spatial variation of sea ice in the NWP is insufficient.Based on the observed sea ice concentration and simulated thickness data,the temporal and spatial characteristics of sea ice concentration,extent and thickness from 1979 to 2017 in the NWP of the CAA were studied.The more specific pathways of the northern and southern routes of the NWP were evaluated.Against the background of the rapid retreat of Arctic sea ice,the 39-year observed sea ice concentration and extent of the NWP exhibited a relatively large decreasing trend in summer and fall,while heavy sea ice conditions were maintained in winter and spring,with slightly increasing trend in some subregions.The sea ice thickness in most subregions of the NWP showed a decreasing trend,with exception of Lancaster Sound.The sea ice thickness was larger along the northern route than the southern routes.The significant correlation (p ＜ 0.05) between sea ice and surface air temperature (SAT) and sea surface temperature (SST) in the NWP suggested that the surface thermodynamic factors had a greater impact on sea ice in the summer and fall,and the variations of sea ice concentration were more closely correlated with the surface thermodynamic factors than sea ice thickness.The SST had a higher correlation with sea ice concentration than SAT,while SAT exhibited a higher correlation with sea ice thickness than SST.The remaining sea ice concentration and thickness in the fall,associated with the summer and fall SAT and SST,contributed to the formation of sea ice in the following winter and spring.The heat content and mixed layer depth were also be considered as the vertical thermodynamic factors to the sea ice condition in the NWP.
查看更多>>摘要：Evaluation of vegetation structure and distribution simulations in Earth system models (ESMs) is the basis for understanding historical reconstruction and future projection of changes in terrestrial ecosystems,carbon cycle,and climate based on these ESMs.Such assessments can also provide important information of models' merits and shortcomings or systematic biases,and so clues for model development.Vegetation structure and distribution in ESMs are primarily characterized by three variables:leaf area index (LAI),tree height,and fractional coverage of plant functional type (PFT).However,for the ongoing Coupled Model Intercomparison Project Phase 6 (CMIP6),only temporal variabilities of global-averaged LAI time series were evaluated,others remain largely uninvestigated.This study systematically investigates the spatial and/or temporal variability of the three critical variables from 27 ESMs in CMIP6 using satellite observations.Our results show that all models and the multi-model ensemble mean (MME) can generally reproduce the observed LAI spatial pattern but all of them overestimate the global mean LAI mainly due to overestimation of LAI in non-forested vegetated areas.Most CMIP6 models fail to capture the temporal variability in the annual LAI because of large biases in both the simulated trend magnitude and temporal pattern of interannual variability.The average LAI seasonal cycles in different latitude zones are roughly reproduced by the models,but 1-2 months delays in the LAI peak appear in the Arctic-boreal zone.Additionally,CMIP6 models overall overestimate tree height,and largely overestimate the global grass area but underestimate tree and shrub areas,especially in the middle and high latitudes.It should be kept in mind that such biases may have further impacts on the simulations of the related carbon and land-atmosphere interaction variables (e.g.,ecosystem production,carbon storage,transpiration,and temperature) for global change research.Hence,bias-correction should be made to improve reliability of vegetation structure and distribution when future projections and historical reconstructions.They also underscore the urgent need in development and parameterization of dynamic vegetation within Earth system models,such as phenology,allocation,and morphology schemes.
查看更多>>摘要：To provide a scientific basis for the policies for the development of wind energy and towards the goal of carbon neutrality in China and local governments,changes in wind energy potential over China were investigated based on the bias-corrected ensemble mean (CENS) of high-resolution dynamical downscaling projections using the RCP2.6,RCP4.5 and RCP8.5 emission scenarios.Firstly,evaluation indicated that CENS could better reproduce the long-term mean and interannual variability of surface wind speed over China compared to the original simulation outputs,providing a reliable basis for future projections.Projection of the averaged wind power density of China showed a decreasing trend during 2020-2099 in all four seasons under all three scenarios,with the significant (p ＜ 0.05) magnitude apparent in both autumn and winter,characterized by an increase over South China and a decrease over northwestern and southwestern regions.In addition,the 'very abundant'and 'abundant'categories of available wind energy located in northern China and the low-speed wind energy in South China were projected to decrease by the middle and late of the 21st century.Although the projected decrease in annual wind power density ranged from-1.14％ to-0.36％ per decade among the three scenarios,we believe that,considering the strong inter-annual variability and uncertainty involved,these changes would not substantially affect China's future wind energy plans.Also of note was that a low emission scenario could to some extent mitigate the reduction in wind energy potential in the future.Furthermore,we suggest that implementation of newly developed wind power technology should consider the impact of changes in wind energy in different sub-regions (e.g.,the low wind speed region over South China),which is pivotal to China's strategic planning in this sector.
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维普