首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 672 毫秒
1.
The response of the polar atmosphere to the reduction of sea ice area in the Arctic and the rise of sea surface temperature is considered using the atmospheric general circulation model with prescribed boundary conditions on the ocean surface. Boundary conditions include the observed sea ice concentration and the sea surface temperature in recent three decades. The study demonstrates that the reduction of sea ice extent is the major factor contributing to the amplification of the warming in the Arctic. However, the spatiotemporal distribution of the warming is not uniform. It is mostly pronounced in autumn and winter and extends up to the height of about 1 km in the areas of large reduction of sea ice concentration or of its complete disappearance. It is demonstrated that the rise of the sea surface temperature also provides some contribution to the warming in the Arctic. Due to the global warming in recent decades statistically significant changes occurred in the distribution of the sea-level pres sure and geopotential heights in the polar region and at mid-latitudes in autumn, winter, and spring. However, these changes are mainly associated with the increase in the sea surface temperature but not with the reduction of sea ice extent. The study has not revealed any significant ret ationships between ice cover anomalies in the Arctic and the evolution of pressure patterns of the synoptic scale that could contribute to the development of cold weather episodes over Eurasia in winter.  相似文献   

2.
On the longer climatic time scales, changes in the elevation and extent of the Antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes, and contribute significantly to world-wide sea levels. In this paper, a 3-D time-dependent thermomechanical model for the entire ice sheet is presented, that is subsequently used to examine the effects of glacial-interglacial shifts in environmental boundary conditions on its geometry. The model takes into account a coupled ice shelf, grounding-line dynamics, basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields. Ice flow is calculated on a fine mesh (40 km horizontal grid size and 10 layers in the vertical) for grounded and floating ice and a stress transition zone in between at the grounding line, where all stress components contribute in the effective stress in the flow law. There is free interaction between ice sheet and ice shelf, so that the entire geometry is internally generated. A simulation of the present ice sheet reveals that the model is able to yield realistic results. A series of sensitivity experiments are then performed, in which lower temperatures, reduced accumulation rates and lower global sea level stands are imposed, either singly or in combination. By comparing results of pairs of experiments, the effects of each of these environmental changes can be determined. In agreement with glacial-geological evidence, we found that the most pronounced changes show up in the West Antarctic ice sheet configuration. They appear to be essentially controlled by variations in eustatic sea level, whereas typical glacial-interglacial changes in temperature and ice deposition rates tend to balance one another. These findings support the hypothesis that the Antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea-level teleconnections. Grounding occurs more readily in the Weddell sea than in the Ross sea and long time scales appear to be involved: it may take up to 30–40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions. According to these reconstructions, a steady state Antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation.  相似文献   

3.
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   

4.
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   

5.
Sublimation and melt disturb the environmental information obtained from ice core records in the Andes. In two case studies we demonstrate to what extent these post-depositional processes may remove major parts of the accumulated snow cover. Dark ash layers from the Tungurahua eruption changed the albedo of surface snow on Chimborazo glacier (6268 m, 1°30 S,78°36 W, Ecuador) between two ice core drilling campaigns and forced substantial melt. Re-distribution and washout of the chemical constituents shifted the concentration profiles obtained in December 1999 as compared to an equivalent core drilled in December 2000. The stable isotope records showed that approximately the water equivalent (weq) of an annual layer had melted, and that the percolating melt water penetrated within the firn layer to a depth of at least 16.5 m without refreezing. In the second example, from a site on the dry axis between the tropical and extra-tropical precipitation belts, significant loss of accumulated snow layers occurred by sublimation. A surface experiment at Cerro Tapado glacier (5536 m, 30°08 S,69°55 W, Chile) revealed that losses of 2 mm weq (5 mm snow) per day occurred during the dry period following the 1997/98 El Niño. This loss generally included the entire surface layer enriched in stable isotopes, and thus caused minimal disturbance of the isotopic signature (and hence climatic information) of the net accumulation, yet chemical constituents again experienced considerable changes in concentration. From annual layer counting and direct dating it is obvious that the major part of the accumulated ice on both glaciers is younger than 100 years; however, isotopic and chemical variations at least in the basal ice from Cerro Tapado clearly point to climate conditions different from the recent centuries. This evidence is supported by mass balance considerations derived from a glacier-climate model. The possibility of a third type of disturbance aside from sublimation and melting – in this case a significant hiatus in the environmental chronology – also deserves consideration for other icecore records from this region. Potential disruptions or discontinuities need to be carefully evaluated given the profound changes in climatic and glaciological conditions since the Last Glacial Maximum throughout Holocene times.  相似文献   

6.
Peculiarities of the ice situation in the Sea of Azov and the Kerch Strait during the cold winter of 2005/06 are considered using a set of satellite images in the visible range, accumulated at the Southern Research Institute of Marine Fisheries and Oceanography (in Kerch). The ice conditions of the water area over the last years are examined and compared to the climatic data.  相似文献   

7.
Long-term observations for monitoring of the cryosphere   总被引：1，自引：0，他引：1  
John E. Walsh 《Climatic change》1995,31(2-4):369-394
Variations of the cryosphere over decadal-to-century timescales are assessed by a survey of data on sea ice, snow cover, glaciers and ice sheets, permafrost and lake ice. The recent variations are generally consistent across the different cryospheric variables, especially when placed into the context of variations of temperature and precipitation. The recent warming over northern land areas has been accompanied by a decrease of snow cover, particularly during spring; the retreat of mountain glaciers is, in an aggregate sense, compatible with the observed warming; permafrost extent and lake ice duration show similar variations in areas for which data are available. Corresponding trends are not apparent, however, in data for some regions such as eastern Canada, nor in hemispheric sea ice data, especially for winter. The data also suggest an increase of snowfall over high latitudes, including the Antarctic ice sheet.Estimates of both the climatic and the statistical significance of the recent variations are hampered by data inhomogeneities, the shortness of the records of many variables and the absence of central archives for data on several variables. The potential of monitoring by satellite remote sensing has been realized with several variables (extent of sea ice, snow cover). Other cryospheric variables (snow depth, ice sheet elevation, lake ice, mountain glaciers) may be amenable to routine monitoring by satellites pending advances in instrumentation, modifications of satellite orbit, and further developments in signal detection algorithms. The survey of recent variations leads to recommendations concerning the use of historical data,in situ measurements, and remote sensing applications in the monitoring of the cryosphere.  相似文献   

8.
The contributions of expanded continental ice, reduced atmospheric CO2, and changes in land albedo to the maintenance of the climate of the last glacial maximum (LGM) are examined. A series of experiments is performed using an atmosphere-mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination. The model used has been shown to produce a reasonably realistic simulation of the reduced temperature of the LGM (Manabe and Broccoli 1985b). By comparing the results from pairs of experiments, the effects of each of these environmental changes can be determined.Expanded continental ice and reduced atmospheric CO2 are found to have a substantial impact on global mean temperature. The ice sheet effect is confined almost exclusively to the Northern Hemisphere, while lowered CO2 cools both hemispheres. Changes in land albedo over ice-free areas have only a minor thermal effect on a global basis. The reduction of CO2 content in the atmosphere is the primary contributor to the cooling of the Southern Hemisphere. The model sensitivity to both the ice sheet and CO2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum.Substantial changes in Northern Hemisphere tropospheric circulation are found in response to LGM boundary conditions during winter. An amplified flow pattern and enhanced westerlies occur in the vicinity of the North American and Eurasian ice sheets. These alterations of the tropospheric circulation are primarily the result of the ice sheet effect, with reduced CO2 contributing only a slight amplification of the ice sheet-induced pattern.  相似文献   

9.
The analysis of the long-term variability and spatiotemporal conjugacy of formation processes of ice conditions in the water areas of the Laptev, East Siberian, and Chukchi seas is carried out on the basis of the available data on the ice cover conditions in the above seas. On the whole, the type of relationships between the ice processes in the system of East Arctic seas indicates the existence of certain mechanisms generating the wave processes in the climatic system of the Arctic Basin manifested in the phase opposition in the development of ice conditions on the western and eastern peripheries of the basin under consideration. The statistical analysis of series of the ice coverage of water areas under consideration demonstrated that the existence of the long-term trend of this characteristic in some seas has its spatiotemporal features: the probability of the trend existence increases from west to east (from the Laptev Sea to the Chukchi Sea) and the trends are of opposite signs.  相似文献   

10.
The river ice regime is considered a sensitive indicator of climate change and within this study long term changes (in case of River Daugava starting from 1530, but for other studied rivers starting from first half of twentieth century) river ice regimes in the Baltic region have been studied. The ice cover duration on the rivers (17 rivers) in the Baltic countries and Belarus has decreased during the recent decades. In addition to this, long term observational records of ice break on the rivers of the studied region exhibit a pattern of periodic changes in the intensity of ice regime. Both the ice regime and the seasonal river discharge are shown to be strongly influenced by large-scale atmospheric circulation processes over North Atlantic that manifests through close correlation with North Atlantic Oscillation index.  相似文献   

11.
Synoptic activity over the Northern Hemisphere is evaluated in ensembles of ECHAM5/MPI-OM1 simulations for recent climate conditions (20C) and for three climate scenarios (following SRES A1B, A2, B1). A close agreement is found between the simulations for present day climate and the respective results from reanalysis. Significant changes in the winter mid-tropospheric storm tracks are detected in all three scenario simulations. Ensemble mean climate signals are rather similar, with particularly large activity increases downstream of the Atlantic storm track over Western Europe. The magnitude of this signal is largely dependent on the imposed change in forcing. However, differences between individual ensemble members may be large. With respect to the surface cyclones, the scenario runs produce a reduction in cyclonic track density over the mid-latitudes, even in the areas with increasing mid-tropospheric activity. The largest decrease in track densities occurs at subtropical latitudes, e.g., over the Mediterranean Basin. An increase of cyclone intensities is detected for limited areas (e.g., near Great Britain and Aleutian Isles) for the A1B and A2 experiments. The changes in synoptic activity are associated with alterations of the Northern Hemisphere circulation and background conditions (blocking frequencies, jet stream). The North Atlantic Oscillation index also shows increased values with enhanced forcing. With respect to the effects of changing synoptic activity, the regional change in cyclone intensities is accompanied by alterations of the extreme surface winds, with increasing values over Great Britain, North and Baltic Seas, as well as the areas with vanishing sea ice, and decreases over much of the subtropics.  相似文献   

12.
极地海冰是地球气候系统的重要组成部分,也是气候环境变化的指示器和放大器。极地海冰复杂的多尺度物理过程和极地观测资料的匮乏,给海冰模式的研发带来了巨大的挑战。在过去的半个多世纪中,大气-海冰-海洋的复杂相互作用和冰内物理过程在海冰模式中的数学描述取得了重大的进展,但海冰模式对一些重要物理过程的描述仍很不完善,尤其是近年来极地海冰的快速变化及其物理特性的变化,极大地增加了海冰模式物理参数化方案和模拟结果的不确定性。因此,迫切需要具备完善物理过程、适应海冰多尺度快速变化的高分辨率海冰模式,并应用于全球气候变化的研究和预测以及极地的开发利用。本文从海冰模式的发展历程和现状、极地海冰快速变化给海冰模式带来的挑战以及适应极地快速变化海冰模式的改进和发展研究方向三个方面进行了阐述和讨论。  相似文献   

13.
This paper analyzes the influence of flaw polynyas of the seas of the Siberian shelf on the formation of ice conditions in summer based on the ten-day data on the areas of flaw polynyas for 1978–2002 obtained by satellite image processing. The results of forecasts of summer ice conditions in the seas of the Siberian shelf are presented. The correspondence between the forecasts and observed data is 94.7% on average. The interrelation of atmospheric and ice processes is shown for the case when winter atmospheric processes determine ice conditions for the following summer and fall.  相似文献   

14.
全球山地冰冻圈变化、影响与适应   总被引：1，自引：0，他引：1  
冰冻圈是高山地区不可或缺的重要组成部分,居住着全球约10%的人口。近几十年来,冰冻圈变化对山区和周围地区的自然和人类系统产生了广泛而深远的影响,对海洋也发挥着重要作用。IPCC最新发布的《气候变化中的海洋和冰冻圈特别报告》（SROCC）指出,过去几十年全球高山区气温显著升高,使山地冰冻圈发生了大范围显著退缩。观测到的山地（特别是低海拔山区）积雪期缩短、雪深和积雪覆盖范围减小;冰川物质持续亏损,其中全球最大的冰川负物质平衡出现在南安第斯山、高加索山和欧洲中部,亚洲高山区冰川负物质平衡最小;多年冻土温度升高、厚度减薄,地下冰储量减少;河、湖冰持续时间缩短。随着气候持续变暖,山地冰冻圈在21世纪仍将呈继续退缩状态。到21世纪末,低海拔山区积雪深度和积雪期将减少,冰川物质损失继续增加,多年冻土持续退化。冰冻圈变化已经或将改变山地灾害发生频率和强度,并对水资源、生态系统和经济社会系统产生重要影响。应对山地冰冻圈变化应从管理和优化利用冰冻圈资源、加强冰冻圈变化灾害风险的有效治理、增强国际合作及公约制定等适应策略着手开展,增强适应能力,从而有益于推动山地生态系统和经济社会系统可持续发展。  相似文献   

15.
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   

16.
The changes of tropical cyclone (TC) activities in response to influencing environmental conditions have been paid more and more attention to in recent years. The potential contributions of single and multivariate environmental variables to annual TC frequency and intensity from 1970 to 2009 are investigated in this study. Instead of using correlation coefficient that assumes a set of samples satisfying the normal distribution, a quantitative measurement is formulated based on the information theory. The results show that dynamic environmental variables play an important role in variations of TC activities over the western North Pacific, North Atlantic, and eastern Pacific. These dynamic factors include wind shear between 850 and 200 hPa and 850-hPa relative vorticity. However, the effects of thermal factors on TC activities are distinct over different basins. The thermal environmental variables only have significant contributions to TC frequency and intensity over the eastern Pacific as well as to TC frequency over the North Atlantic. It is found that the primary factors influencing TC activities are indeed not the same over different basins because of the differences in atmospheric conditions and their changes across different areas. The effects of dynamic variables should be considered more in the regions such as the western North Pacific where the thermal conditions are always satisfied.  相似文献   

17.
导线覆冰是在一定气象条件下发生的复杂的物理过程,贵州是我国南方导线覆冰最严重的受灾区,每年都会发生不同程度的覆冰灾害。本文利用地面观测资料、探空资料、NCEP再分析资料和覆冰资料,通过分析影响局地线路覆冰的大范围气候、天气背景及其变化特征,结合已有的覆冰灾害事件,侧重于气候背景的角度,分析总结了2008～2011年贵州产生覆冰的天气气候特征,气象要素条件以及地理环境因子与导线覆冰的关系,主要得出以下结论：贵州省导线覆冰与中高纬大气环流异常,西太平洋副高的北移,对流层下层逆温层的影响密不可分;贵州省地处云贵高原,北边小槽移动影响与南方来的暖湿空气汇集之地,容易形成冰冻天气,加之导线多分布于山上,则导线的材质与分布,导线所在环境的空气湿度,空气温度,风向风速,降水与天气状况等,决定了导线覆冰的厚度。  相似文献   

18.
Presented are the results of studying the regional peculiarities of climatic variations of spatiotemporal distribution of ice in the Barents Sea water area in 1977?C2010. Demonstrated is the dynamics of the interannual and seasonal variability of main elements of the ice regime (ice cover area, ice edge position, and ice period duration). Revealed are the common features and differences in the ice conditions in the water areas under study. It has been found that there is a significant feedback between the specific ice coverage in different areas of the sea. The climatic variations of the total ice coverage of the Barents Sea for the period of 1960?C2010 are analyzed using the electronic database on the Barents Sea ice coverage. It can be supposed that the current warm phase of climatic variations in the Barents Sea is coming to the end.  相似文献   

19.
This reconstruction of the ice winter severity in the Western Baltic is based for the period 1878-1993 on the accumulated areal ice volume along the German Baltic coast with observations from 13 coastal stations; for the period 1701-1877 it is based on the accumulated areal ice volume divided into 7 classes (ice winter severity types). The various types of data consulted in the latter case provided ice data of good spatial and temporal resolution.Speerschneider's compilation of data relating to ice conditions in Danish Baltic waters was found to be a valuable source of information. Using a classification table for the periods 1907-1943 and 1947-1992, five of the seven ice winter types have been derived with certainty as they are characterized by typical stages of maximum ice cover throughout the Western Baltic.The Gaussian lowpass-filtered time series of the ice winter index numerals with a 20 year cutoff period shows four periods of varying ice winter severity over a secular range: 1701-1720: slightly increased ice winter severity with regard to the mean of the 1701-1993 time series; this period can be assigned to the end of a cooling phase during Little Ice Age which in central Europe peaked in the second half of the 17th c. 1721-1760: ice winter severity is clearly reduced in this period. 1761-1860: ice winter severity is clearly increased (maximum occurs around 1800) towards the end of the Little Ice Age, associated with increased variability of ice production. 1861-1993: the present-day ice winter regime when three short intervals with increased ice winter severity (the 1890s, 1940s and 1980s) and a period of greatly reduced ice winter severity (between 1900 and the mid-1920s) stand out.  相似文献   

20.
Variability and change in the Canadian cryosphere   总被引：2，自引：1，他引：1  
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   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号