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1.
Arctic sea ice and Eurasian climate: A review 总被引：12，自引：0，他引：12
GAO Yongqi SUN Jianqi LI Fei HE Shengping Stein SANDVEN YAN Qing ZHANG Zhongshi Katja LOHMANN Noel KEENLYSIDE Tore FUREVIK SUO Lingling 《大气科学进展》2015,32(1):92-114
The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades,including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate.Paleo, observational and modelling studies are covered to summarize several major themes, including: the variability of Arctic sea ice and its controls; the likely causes and apparent impacts of the Arctic sea-ice decline during the satellite era,as well as past and projected future impacts and trends; the links and feedback mechanisms between the Arctic sea ice and the Arctic Oscillation/North Atlantic Oscillation, the recent Eurasian cooling, winter atmospheric circulation, summer precipitation in East Asia, spring snowfall over Eurasia, East Asian winter monsoon, and midlatitude extreme weather; and the remote climate response(e.g., atmospheric circulation, air temperature) to changes in Arctic sea ice. We conclude with a brief summary and suggestions for future research. 相似文献
2.
Qinghua YANG Jiping LIU Matti LEPPRANTA Qizhen SUN Rongbin LI Lin ZHANG Thomas JUNG Ruibo LEI Zhanhai ZHANG Ming LI Jiechen ZHAO Jingjing CHENG 《大气科学进展》2016,33(5):535-543
The snow/sea-ice albedo was measured over coastal landfast sea ice in Prydz Bay, East Antarctica(off Zhongshan Station)during the austral spring and summer of 2010 and 2011. The variation of the observed albedo was a combination of a gradual seasonal transition from spring to summer and abrupt changes resulting from synoptic events, including snowfall, blowing snow, and overcast skies. The measured albedo ranged from 0.94 over thick fresh snow to 0.36 over melting sea ice. It was found that snow thickness was the most important factor influencing the albedo variation, while synoptic events and overcast skies could increase the albedo by about 0.18 and 0.06, respectively. The in-situ measured albedo and related physical parameters(e.g., snow thickness, ice thickness, surface temperature, and air temperature) were then used to evaluate four different snow/ice albedo parameterizations used in a variety of climate models. The parameterized albedos showed substantial discrepancies compared to the observed albedo, particularly during the summer melt period, even though more complex parameterizations yielded more realistic variations than simple ones. A modified parameterization was developed,which further considered synoptic events, cloud cover, and the local landfast sea-ice surface characteristics. The resulting parameterized albedo showed very good agreement with the observed albedo. 相似文献
3.
V. P. Meleshko V. M. Kattsov A. V. Baidin T. V. Pavlova V. A. Govorkova 《Russian Meteorology and Hydrology》2016,41(11-12):735-746
The effects are considered that global warming and rapid sea ice decline in the Arctic (up to the formation of ice-free conditions in the Arctic Ocean in summer) made on the hydrological regime of Northern Eurasia. Ensemble computations of climate are provided and changes in the atmospheric water cycle and in water balance in large catchment areas after the loss of multiyear sea ice in the Arctic are estimated. Considerable changes in the hydrological regime are demonstrated on the example of the large catchments of the Siberian rivers; the changes are especially manifested in the period of intense snow melting, i.e., in spring and in early summer. It is revealed that the increase in the frequency of spring floods is expected in the river catchments adjoining the Arctic Ocean. It is demonstrated that the Arctic Ocean ice reduction does not exert as significant influence on variations in the water cycle in Northern Eurasia as the global warming does. 相似文献
4.
Submarine and satellite observations show that the Arctic Ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades. Here the response of the Arctic Ocean ice cover to changes in the poleward atmospheric energy transport, F wall, is investigated using coupled atmosphere-ice-ocean column models. Two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness—ice volume export feedback and the positive surface albedo feedback. The steady state ice thickness as a function of F wall is determined for various model setups and defines what we call ice thickness response curves. When a variable surface albedo and snow precipitation is included, a complex response curve appears with two distinct regimes: a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime. The two regimes are separated by a steep transition associated with surface albedo feedback. The associated hysteresis is however small, indicating that the Arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback. The results are discussed in the context of the recent reduction of the Arctic sea ice cover. A new mechanism related to regional and temporal variations of the ice divergence within the Arctic Ocean is presented as an explanation for the observed regional variation of the ice thickness reduction. Our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i.e. large areas of the Arctic Ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness, corresponding to the above mentioned transition, and into a state dominated by seasonal ice. 相似文献
5.
北极海冰融化影响东亚冬季天气和气候的研究进展以及学术争论焦点问题 总被引：3，自引：1，他引：2
北极历来是影响东亚冬季天气、气候的关键区域之一。北极表面增暖要比全球平均快2~3倍,即所谓北极的放大效应。随着全球增暖的持续以及北极海冰的持续融化,北极的生态环境正在发生显著的变化,进而可能对北半球中、低纬度的天气、气候产生影响。本文概述了有关北极海冰融化影响冬季东亚天气、气候的主要研究进展,特别是自2000年以来,北极海冰异常偏少影响东亚冬季气候变率以及极端严寒事件的可能途径、存在的科学问题,以及学术界的争论焦点。秋、冬季节是北极海冰快速形成时期,此时北极海冰对大气环流的影响要强于大气对海冰的影响。近二十年来的研究结果表明,北极海冰异常偏少,不仅影响北冰洋局地的气温和降水变化,而且通过复杂的相互作用和反馈过程,对北半球中、低纬度的天气、气候产生影响。北极海冰通过以下两个可能机制来影响东亚冬季的天气、气候:（1）北极海冰的负反馈机制;（2）由海冰异常偏少引起的平流层-对流层相互作用机制。秋、冬季节北极海冰持续异常偏少,特别是,巴伦支海-喀拉海海冰异常偏少,既可以加强冬季西伯利亚高压（东亚冬季风偏强）,也可以导致冬季风偏弱。导致海冰影响不确定性的部分原因是:（1）夏季北极大气环流状态影响北极海冰异常偏少对冬季大气环流的反馈效果;（2）冬季大气环流对北极海冰异常偏少响应的位置、强度不同造成的。秋、冬季节北极海冰持续异常偏少,在适宜的条件下（例如,前期夏季北极大气环流的热力和动力条件,有利于加强北极海冰偏少对冬季大气的反馈作用）,可以激发出有利于冬季亚洲大陆极端严寒过程的大气环流异常。目前学术界争论焦点主要集中在以下两个方面:（1）关于北极增暖、北极海冰融化对中纬度区域影响的争论;（2）关于1980年代后期以来,冬季欧亚大陆表面气温呈现降温趋势的原因。目前,有关北极海冰融化影响冬季欧亚大陆次季节变化以及极端天气、气候事件的过程和机制,我们认知非常有限,亟需开展深入细致的研究。 相似文献
6.
Based on the NCEP/NCAR reanalysis data and Chinese observational data during 1961–2013, atmospheric circulation patterns over East Asia in summer and their connection with precipitation and surface air temperature in eastern China as well as associated external forcing are investigated. Three patterns of the atmospheric circulation are identified, all with quasi-barotropic structures: (1) the East Asia/Pacific (EAP) pattern, (2) the Baikal Lake/Okhotsk Sea (BLOS) pattern, and (3) the eastern China/northern Okhotsk Sea (ECNOS) pattern. The positive EAP pattern significantly increases precipitation over the Yangtze River valley and favors cooling north of the Yangtze River and warming south of the Yangtze River in summer. The warm sea surface temperature anomalies over the tropical Indian Ocean suppress convection over the northwestern subtropical Pacific through the Ekman divergence induced by a Kelvin wave and excite the EAP pattern. The positive BLOS pattern is associated with below-average precipitation south of the Yangtze River and robust cooling over northeastern China. This pattern is triggered by anomalous spring sea ice concentration in the northern Barents Sea. The anomalous sea ice concentration contributes to a Rossby wave activity flux originating from the Greenland Sea, which propagates eastward to North Pacific. The positive ECNOS pattern leads to below-average precipitation and significant warming over northeastern China in summer. The reduced soil moisture associated with the earlier spring snowmelt enhances surface warming over Mongolia and northeastern China and the later spring snowmelt leads to surface cooling over Far East in summer, both of which are responsible for the formation of the ECNOS pattern. 相似文献
7.
Modelling the influence of snow accumulation and snow-ice formation on the seasonal cycle of the Antarctic sea-ice cover 总被引：5，自引：5，他引：0
Recent observational and numerical studies of the maritime snow cover in the Antarctic suggest that snow on top of sea ice
plays a major role in shaping the seasonal growth and decay of the ice pack in the Southern Ocean. Here, we make a quantitative
assessment of the importance of snow accumulation in controlling the seasonal cycle of the ice cover with a coupled snow–sea-ice–upper-ocean
model. The model takes into account snow and ice sublimation and snow deposition by condensation. A parametrisation of the
formation of snow ice (ice resulting from the freezing of a mixture of snow and seawater produced by flooding of the ice floes)
is also included. Experiments on the sensitivity of the snow–sea-ice system to variations in the sublimation/condensation
rate, the precipitation rate, and the amount of snowfall transported by the wind into leads are discussed. Although we focus
on the model response in the Southern Hemisphere, results for the Arctic are also discussed in some cases to highlight the
relative importance of the processes under study in both hemispheres. It is found that the snow loss by sublimation can account
for the removal of 0.45 m of snow per year in the Antarctic and that this loss significantly affects the total volume of snow
ice. A precipitation decrease of 50% is conducive to large reductions in the Antarctic snow and snow-ice volumes, but it leads
only to an 8% decrease in the annual mean ice volume. The Southern Ocean ice pack is more sensitive to increases in precipitation.
For precipitation rates 1.5 times larger than the control ones, the annual mean snow, ice, and snow-ice volumes augment by
30, 20, and 180%, respectively. It is also found that the transfer to the ocean of as much as 50% of the precipitating snow
as a result of wind transport has almost negligible effects on the total ice volume. All the experiments exhibit a marked
geographical contrast in the ice-cover response, with a much larger sensitivity in the western sector of the Southern Ocean
than in the eastern sector. Our results suggest that snow-related processes are of secondary importance for determining the
sensitivity of the Arctic sea ice to environmental changes but that these processes could have an important part to play in
the response of the Antarctic sea-ice cover to future, or current, climatic changes.
Received: 30 June 1997/Accepted: 2 October 1998 相似文献
8.
全球气候变暖中南北半球海冰变化的差异 总被引：4，自引：0，他引：4
应用海冰面积资料,分析在全球气候变暖下,南北半球海冰季节和年际变化的差异,结果表明:冬季南半球海冰面积为北半球的1.13倍,而夏季仅为北半球的2/5,南半球海冰的季节变化比北半球更为显著,其季节振幅为北半球的1.6倍.1979--2006年,北半球海冰总面积呈显著减少趋势,夏秋季最快,特别在1990年代中后期以来,减少尤为迅速;夏秋季,整个区域海冰为均一的减少趋势,北冰洋靠近北太平洋的近海变化最为迅速,冬春季,主要发生在北太平洋海域.南半球海冰自1980年代初以来有所增多,四季整个区域海冰并未呈均一的减少趋势,而是有一显著减少中心,位于南极半岛附近,两个增多中心,分别位于罗斯海外围和西南印度洋一带.随夏一秋一冬一春的季节转换,3个中心区域位置存在东移和返回的过程. 相似文献
9.
《大气与海洋》2013,51(3):224-237
Abstract The University of Victoria's (UVic) Earth System Climate model is used to conduct equilibrium atmospheric CO2 sensitivity experiments over the range 200–1600 ppm in order to explore changes in northern hemisphere snow cover and feedbacks on terrestrial surface air temperature (SAT). Simulations of warmer climates predict a retreat of snow cover over northern continents, in a northeasterly direction. The decline in northern hemisphere global snow mass is estimated to reach 33% at 600 ppm and 54% at 1200 ppm. In the most northerly regions, annual mean snow depth increases for simulations with CO2 levels higher than present day. The shift in the latitude of maximum snowfall is estimated to be inversely proportional to the CO2 concentration. The northern hemisphere net shortwave radiation changes are found to be greater over land than over the ocean, suggesting a stronger albedo feedback from changes in terrestrial snow cover than from changes in sea ice. Results also reveal high sensitivity of the snow mass balance under low CO2 conditions. The amplification feedback (defined as the zonal SAT anomaly caused by doubling CO2 divided by the equatorial anomaly) is greatest for scenarios with less than 300 ppm, reaching 1.9 at the pole for 250 ppm. The stronger feedback is attributed to the significant albedo changes over land areas. The simulation with 200 ppm triggers continuous accumulation of snow ('glaciation') in regions which, according to paleo‐reconstructions, were covered by ice during the last glacial cycle (the Canadian Arctic, Scandinavia, and the Taymir Peninsula). 相似文献
10.
Simulations of the Arctic sea ice cover over the last 32 years generated by the HadGEM1 coupled climate model are able to capture the observed long term decline in mean September ice extent. HadGEM1 is also capable of producing an episode of low September ice extent of similar magnitude to the anomalously low extent observed in 2007. Using a heat budget analysis, together with diagnostics partitioning the changes in ice and snow mass into thermodynamic and dynamic components, we analyse the factors driving the long term decline in the ice mass and extent as well as those causing the modelled low ice event. The long term decline in the mass of ice and snow in HadGEM1 is largely due to extra melting during the summer, partly at the top surface of the ice, and partly via extra heating from the ocean as it warms due to the ice retreat. The episode of low summer ice extent is largely driven by the synoptic conditions over the summer moving the ice across and out of the Arctic basin, and also due to pre-conditioning of the snow and ice which is thinner than usual in the Eastern Arctic at the start of the melt season. This case study demonstrates that although HadGEM1 does not capture the persistent dipole pressure anomaly observed during the summer of 2007, it represents broadly similar mechanisms of generating a low ice extent. 相似文献
11.
东亚季风近几十年来的主要变化特征 总被引：14，自引：4，他引：10
本文简要综述了关于东亚夏季风和冬季风近几十年来的主要变化特征的若干研究结果,特别是关于其年代际变化方面.夏季风及夏季气候的主要变化特征有:1970年代末之后东亚夏季风的年代际时间尺度的减弱以及相应的我国夏季降水江淮流域增多而华北减少、1992年之后我国华南夏季降水增多、1999年之后我国长江中下游夏季降水减少而淮河流域夏季降水增多、东亚夏季风和ENSO之间的年际变化相关性存在不稳定性.而关于东亚冬季风与冬季气候的主要变化特征有:1980年代中期之后东亚冬季风及其年际变率减弱、1970年代中期之后冬季风和ENSO的年际变化相关性较弱、近年来的北极秋季海冰减少对北半球冬季积雪增多有显著贡献、东北冬季积雪在1980年代中期以后增多.与上述变化有关的极端气候和物候都发生了多方面的变化. 相似文献
12.
Torben Koenigk Laurent Brodeau Rune Grand Graversen Johannes Karlsson Gunilla Svensson Michael Tjernström Ulrika Willén Klaus Wyser 《Climate Dynamics》2013,40(11-12):2719-2743
The Arctic climate change is analyzed in an ensemble of future projection simulations performed with the global coupled climate model EC-Earth2.3. EC-Earth simulates the twentieth century Arctic climate relatively well but the Arctic is about 2 K too cold and the sea ice thickness and extent are overestimated. In the twenty-first century, the results show a continuation and strengthening of the Arctic trends observed over the recent decades, which leads to a dramatically changed Arctic climate, especially in the high emission scenario RCP8.5. The annually averaged Arctic mean near-surface temperature increases by 12 K in RCP8.5, with largest warming in the Barents Sea region. The warming is most pronounced in winter and autumn and in the lower atmosphere. The Arctic winter temperature inversion is reduced in all scenarios and disappears in RCP8.5. The Arctic becomes ice free in September in all RCP8.5 simulations after a rapid reduction event without recovery around year 2060. Taking into account the overestimation of ice in the twentieth century, our model results indicate a likely ice-free Arctic in September around 2040. Sea ice reductions are most pronounced in the Barents Sea in all RCPs, which lead to the most dramatic changes in this region. Here, surface heat fluxes are strongly enhanced and the cloudiness is substantially decreased. The meridional heat flux into the Arctic is reduced in the atmosphere but increases in the ocean. This oceanic increase is dominated by an enhanced heat flux into the Barents Sea, which strongly contributes to the large sea ice reduction and surface-air warming in this region. Increased precipitation and river runoff lead to more freshwater input into the Arctic Ocean. However, most of the additional freshwater is stored in the Arctic Ocean while the total Arctic freshwater export only slightly increases. 相似文献
13.
V. P. Meleshko V. M. Kattsov V. M. Mirvis A. V. Baidin T. V. Pavlova V. A. Govorkova 《Russian Meteorology and Hydrology》2018,43(11):743-755
Studies dealing with impact of the Arctic warming and related sea ice decline on the Northern Hemisphere atmospheric circulation are considered. The causes of occurrence of extremely cold winters over the mid-latitude continents observed in the recent decades against the warming background are discussed. Several conceptions are outlined which explain potential reasons for occurrence of this phenomenon. The paper discusses impacts of the Arctic sea ice loss on the large-scale atmospheric circulation, oscillations of planetary waves. It also discusses issues related to sea ice changes in the Barents and Kara seas and their link to the frequency of extremely cold winters observed in Eurasia and North America, the contribution of internal atmospheric variability to the increasing frequency of cold weather, and the role of the Atlantic Multidecadal Oscillation in the Arctic sea ice reduction. 相似文献
14.
Sea ice formed over shallow Arctic shelves often entrains sediments resuspended from the sea floor. Some of this sediment-laden ice advects offshore into the Transpolar Drift Stream and the Beaufort Gyre of the Arctic Basin. Through the processes of seasonal melting at the top surface, and the freezing of clean ice on the bottom surface, these sediments tend, over time, to concentrate at the top of the ice where they can affect the surface albedo, and thus the absorbed solar radiation, when the ice is snow free. Similarly, wind-blown dust can reduce the albedo of snow. The question that is posed by this study is what is the impact of these sediments on the seasonal variation of sea ice, and how does it then affect climate? Experiments were conducted with a coupled energy balance climate-thermodynamic sea ice model to examine the impact of including sediments in the sea ice alone and in the sea ice and overlying snow. The focus of these experiments was the impact of the radiative and not the thermal properties of the sediments. The results suggest that if sea ice contains a significant amount of sediments which are covered by clean snow, there is only a small impact on the climate system. However, if the snow also contains significant sediments the impact on sea ice thickness and surface air temperature is much more significant. 相似文献
15.
The Arctic’s rapidly shrinking sea ice cover: a research synthesis 总被引：21，自引：1，他引：20
Julienne C. Stroeve Mark C. Serreze Marika M. Holland Jennifer E. Kay James Malanik Andrew P. Barrett 《Climatic change》2012,110(3-4):1005-1027
The sequence of extreme September sea ice extent minima over the past decade suggests acceleration in the response of the Arctic sea ice cover to external forcing, hastening the ongoing transition towards a seasonally open Arctic Ocean. This reflects several mutually supporting processes. Because of the extensive open water in recent Septembers, ice cover in the following spring is increasingly dominated by thin, first-year ice (ice formed during the previous autumn and winter) that is vulnerable to melting out in summer. Thinner ice in spring in turn fosters a stronger summer ice-albedo feedback through earlier formation of open water areas. A thin ice cover is also more vulnerable to strong summer retreat under anomalous atmospheric forcing. Finally, general warming of the Arctic has reduced the likelihood of cold years that could bring about temporary recovery of the ice cover. Events leading to the September ice extent minima of recent years exemplify these processes. 相似文献
16.
Variability and change in the Canadian cryosphere 总被引：2，自引：1，他引：1
C. Derksen S. L. Smith M. Sharp L. Brown S. Howell L. Copland D. R. Mueller Y. Gauthier C. G. Fletcher A. Tivy M. Bernier J. Bourgeois R. Brown C. R. Burn C. Duguay P. Kushner A. Langlois A. G. Lewkowicz A. Royer A. Walker 《Climatic change》2012,115(1):59-88
During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing systems and retrieval algorithms for satellite measurements facilitated development of a snapshot of current cryospheric conditions, providing a baseline against which future change can be assessed. Key findings include: 1. surface air temperatures across the Canadian Arctic exhibit a warming trend in all seasons over the past 40?years. A consistent pan-cryospheric response to these warming temperatures is evident through the analysis of multi-decadal datasets; 2. in recent years (including the IPY period) a higher rate of change was observed compared to previous decades including warming permafrost, reduction in snow cover extent and duration, reduction in summer sea ice extent, increased mass loss from glaciers, and thinning and break-up of the remaining Canadian ice shelves. These changes illustrate both a reduction in the spatial extent and mass of the cryosphere and an increase in the temporal persistence of melt related parameters. The observed changes in the cryosphere have important implications for human activity including the close ties of northerners to the land, access to northern regions for natural resource development, and the integrity of northern infrastructure. 相似文献
17.
Amplified Arctic warming is one of the key features of climate change. It is evident in observations as well as in climate model simulations. Usually referred to as Arctic amplification, it is generally recognized that the surface albedo feedback governs the response. However, a number of feedback mechanisms play a role in AA, of which those related to the prevalent near-surface inversion have received relatively little attention. Here we investigate the role of the near-surface thermal inversion, which is caused by radiative surface cooling in autumn and winter, on Arctic warming. We employ idealized climate change experiments using the climate model EC-Earth together with ERA-Interim reanalysis data to show that boundary-layer mixing governs the efficiency by which the surface warming signal is ‘diluted’ to higher levels. Reduced vertical mixing, as in the stably stratified inversion layer in Arctic winter, thus amplifies surface warming. Modelling results suggest that both shortwave—through the (seasonal) interaction with the sea ice feedback—and longwave feedbacks are affected by boundary-layer mixing, both in the Arctic and globally, with the effect on the shortwave feedback dominating. The amplifying effect will decrease, however, with climate warming because the surface inversion becomes progressively weaker. We estimate that the reduced Arctic inversion has slowed down global warming by about 5% over the past 2 decades, and we anticipate that it will continue to do so with ongoing Arctic warming. 相似文献
18.
The Arctic Amplification Debate 总被引：16，自引：0，他引：16
Rises in surface air temperature (SAT) in response to increasing concentrations of greenhouse gases (GHGs) are expected to be amplified in northern high latitudes, with warming most pronounced over the Arctic Ocean owing to the loss of sea ice. Observations document recent warming, but an enhanced Arctic Ocean signal is not readily evident. This disparity, combined with varying model projections of SAT change, and large variability in observed SAT over the 20th century, may lead one to question the concept of Arctic amplification. Disparity is greatly reduced, however, if one compares observed trajectories to near-future simulations (2010–2029), rather than to the doubled-CO2 or late 21st century conditions that are typically cited. These near-future simulations document a preconditioning phase of Arctic amplification, characterized by the initial retreat and thinning of sea ice, with imprints of low-frequency variability. Observations show these same basic features, but with SATs over the Arctic Ocean still largely constrained by the insulating effects of the ice cover and thermal inertia of the upper ocean. Given the general consistency with model projections, we are likely near the threshold when absorption of solar radiation during summer limits ice growth the following autumn and winter, initiating a feedback leading to a substantial increase in Arctic Ocean SATs. 相似文献
19.
Onset and end of the summer melt season over sea ice: thermal structure and surface energy perspective from SHEBA 总被引：1，自引：0，他引：1
P. Ola G. Persson 《Climate Dynamics》2012,39(6):1349-1371
Various measurements from the Surface Heat Flux of the Arctic Ocean (SHEBA) experiment have been combined to study structures and processes producing the onset and end of summer melt over Arctic sea ice. The analysis links the surface energy budget to free-troposphere synoptic variables, clouds, precipitation, and in-ice temperatures. The key results are (1) SHEBA melt-season transitions are associated with atmospheric synoptic events (2) onset of melt clearly occurs on May 28, while the end of melt is produced by a sequence of three atmospheric storm events over a 28-day period producing step-like reductions in the net surface energy flux. The last one occurs on August 22.; (3) melt onset is primarily due to large increases in the downwelling longwave radiation and modest decreases in the surface albedo; (4) decreases in the downwelling longwave radiation occur for all end-of-melt transition steps, while increases in surface albedo occur for the first two; (5) decreases in downwelling shortwave radiation contribute only to the first end-of-melt transition step; (6) springtime free-tropospheric warming preconditions the atmosphere–ice system for the subsequent melt onset; and (7) melt-season transitions also mark transitions in system responses to radiative energy flux changes because of invariant melt-season surface temperatures. The extensive SHEBA observations enable an understanding of the complex processes not available from other field program data. The analysis provides a basis for future testing of the generality of the results, and contributes to better physical understanding of multi-year analyses of melt-season trends from less extensive data sets. 相似文献
20.
20世纪90年代末东亚冬季风年代际变化的外强迫因子分析 总被引：1，自引：0，他引：1
使用NCEP/NCAR、英国气象局哈德莱中心(Met Office Hadley Center)Had ISST以及NOAA提供的再分析资料分析了海温、海冰及雪盖异常对20世纪90年代末我国冬季气温和东亚冬季风(EAWM)年代际跃变的外部强迫作用,同时也对比分析了20世纪90年代EAWM年代际跃变与20世纪80年代EAWM年代际跃变特征和成因的一些差异。结果表明:20世纪80年代中期EAWM的年代际变化特征主要表现为全国一致偏冷型,同时中国近海的海温也偏低;该年代际变化的主要原因来自大气内部动力过程,而海温和海冰的作用不显著。20世纪90年代末EAWM年代际变化的特征表现为东亚北方气温显著偏冷而南方偏暖的南北反相变化分布;EAWM在20世纪90年代末的年代际变化受北大西洋海温和热带太平洋海温的共同影响。北大西洋显著的异常暖海温,激发一个向下游传播的波列,使得西伯利亚高压加强,EAWM加强,从而导致我国北方气温下降;同时,秋冬季北极海冰异常偏少和秋季欧亚雪盖偏多对东亚冬季风的增强也有一定的作用。此外,热带西太平洋的暖海温异常会导致在海洋性大陆地区有异常的辐合和对流增强,引起大气环流的Gill型响应,对流西侧的异常气旋在孟加拉湾至我国西南地区出现南风异常,使得东亚南部地区温度偏高。因此,20世纪90年代末之后东亚温度呈现南暖北冷的分布特征。 相似文献