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1.
Samples of surface snow were collected for stable isotope analysis along the traverse route from Zhongshan to Dome A (East Antarctica) from Dec 28th, 2007 to Feb. 8th, 2008. The local relationship between δD and surface temperature is established to be 6.4 ± 0.2 ‰ per °C, very similar to the average for East Antarctic. The deuterium excess shows a pattern of high values over Antarctica, particularly at Dome A. We compare our data with an atmospheric general circulation model which includes stable water isotopes (ECHAM5-wiso). The model simulation captures the right levels of δD, but overestimates δ18O. This study provides support for the ongoing deep ice core project at Dome A.  相似文献   

2.
Stable isotopes in water have been measured along a very high accumulation ice core from Law Dome on the east Antarctic coast. These enable a detailed comparison of the isotopic records over sixty years (1934–1992) with local (Antarctic station data) and remote meteorological observations (atmospheric reanalyses and sea-surface temperature estimates) on a seasonal to inter-annual time scale. Using both observations and isotopic atmospheric general circulation model (GCM) results, we quantify the relationships between stable isotopes (d 18O, dD and deuterium excess; d = dD –8 × d 18O) with site and source temperature at seasonal and decadal time scales, showing the large imprint of source conditions on Law Dome isotopes. These calibrations provide new insights for the quantitative interpretation of temporal isotopic fluctuations from coastal Antarctic ice cores. An abrupt change in the local meridional atmospheric circulation is clearly identified from Law Dome deuterium excess during the 1970s and analysed using GCM simulations.  相似文献   

3.
Mid-latitude winter atmospheric variability in the South Indian Ocean and southwest Pacific Ocean regions of the circum-Antarctic are reconstructed using sea-salt aerosol concentrations measured in the high resolution Law Dome (DSS) ice core from East Antarctica. The sea-salt aerosol concentration data, as sodium (Na), were measured at approximately monthly resolution spanning the past 700 years. Analyses of covariations between Na concentrations in Law Dome ice, and mean sea-level pressure (MSLP) and wind field data were conducted to define the mid-latitude and sub-Antarctic atmospheric circulation patterns associated with variations in Na delivery. High Na concentrations in Law Dome snow are associated with increased meridional aerosol transport from mid-latitude sources. The seasonal average Na concentration for early winter (May, June, July (MJJ)) is strongly correlated to the mid-latitude MSLP field in the South Indian and southwest Pacific Oceans, and southern Australian regions. In addition, the average MJJ Na concentrations display a strong association with the stationary Rossby wave number 3 circulation, and are anti-correlated to the Southern Annular Mode (SAM) index of climate variability: high (low) Na concentrations occurring during negative (positive) SAM phases. This observed relationship is used to derive a proxy record for early-winter MSLP anomalies and the SAM in the South Indian and southwest Pacific Ocean regions over the period 1300–1995 AD. The proxy SAM index from 1300 to 1995 AD shows pronounced decadal-scale variability throughout. The period after 1500 AD is marked by a tendency toward slower variations and a weakly-positive mean SAM (enhanced westerlies in the 50° to 65°S zone) compared to the early part of the record.  相似文献   

4.
Snow precipitation is the primary mass input to the Antarctic ice sheet and is one of the most direct climatic indicators, with important implications for paleoclimatic reconstruction from ice cores. Provenance of precipitation and the dynamic conditions that force these precipitation events at four deep ice core sites (Dome C, Law Dome, Talos Dome, and Taylor Dome) in East Antarctica were analysed with air mass back trajectories calculated using the Lagrangian model and the mean composite data for precipitation, geopotential height and wind speed field data from the European Centre for Medium Range Weather Forecast from 1980 to 2001. On an annual basis, back trajectories showed that the Atlantic-Indian and Ross-Pacific Oceans were the main provenances of precipitation in Wilkes Land (80%) and Victoria Land (40%), respectively, whereas the greatest influence of the ice sheet was on the interior near the Vostok site (80%) and in the Southwest Ross Sea (50%), an effect that decreased towards the coast and along the Antarctic slope. Victoria Land received snowfall atypically with respect to other Antarctica areas in terms of pathway (eastern instead of western), seasonality (summer instead of winter) and velocity (old air age). Geopotential height patterns at 500 hPa at low (>10 days) and high (2–6 days) frequencies during snowfall cycles at two core sites showed large positive anomalies at low frequencies developing in the Tasman Sea-Eastern Indian Ocean at higher latitudes (60–70°S) than normal. This could be considered part of an atmospheric blocking event, with transient eddies acting to decelerate westerlies in a split region area and accelerate the flow on the flanks of the low-frequency positive anomalies.  相似文献   

5.
This paper summarizes the long-term fluctuations of snow accumulation in the Antarctic and analyzes its correlation with the sea level pressure (SLP) in the middle latitude (40°–50° S) of the Southern Hemisphere. Stratigraphic data which were compiled from studies on ice cores and snow-pits at eight stations in the Antarctic were used in the present study. It was found that the data concerning fluctuations in snow accumulation for East Antarctica showed correlations, whereas no such correlation was observed for the data from West Antarctica.This study shows possible relationships between snow accumulation in the Antarctic and SLP in the middle latitudes. The fluctuations of accumulation at South Pole, Dome C, Wilkes and South Ice Point show correlations with SLP over a large area in the 40°–50° S latitudinal zone. For the long-term fluctuations of SLP in the 40°–50 ° S latitudinal zone, a zonal fluctuation with wave number zero structure and a longitudinal variation of SLP anomalies due to their out-of-phase-fluctuation between the Pacific and the Indian Oceans were observed. The temporal scales for these fluctuations were found to be in the order of 20–30 years and 40–60 years, respectively. The influences of these two modes on the behaviour of snow accumulation in the Antarctic is also discussed.Now at Kitami Institute of Technology, Kitami, Hokkaido, Japan.  相似文献   

6.
A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model (RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than 60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations.  相似文献   

7.
We have examined several MSA (methanesulfonic acid) records from the upper 200 m of the Antarctic ice sheet and in particular the new Dome F profile. At all the four sites studied, concentration profiles exhibit similar patterns as a function of depth. They suggest that snow metamorphism and solid phase migration are responsible for a marked release of gaseous MSA to interstitial firn air as well as probably to the free atmosphere, in particular at extremely low accumulation sites. Snow acidity can also modify MSA concentration. It is proposed that, below the upper few metres where the communication with the free atmosphere is possible, gaseous MSA may remain in the firn layers and be entrapped later in air bubbles at pore close-off, i.e. when firn is transformed into ice. Chemical measurements on the firn core do not take into account the MSA released to the gaseous phase, but this fraction is measurable in ice samples. In spite of these alterations occurring in the firn layers, relative changes of the atmospheric MSA concentration in the past are probably still there deep within the Antarctic ice sheet. However, for glacial periods, different processes have to be considered in relation to modified aerosol properties.  相似文献   

8.
Simultaneous measurements of soluble and insoluble impurities were made on the 950 m deep Vostok (78°30′S, 106°54′E, 3420 m a.s.l.) ice core, spanning roughly 50000 yr, using various analytical techniques. We observed higher continental (×37) and marine (×5.1) inputs during the last glacial age than during the Holocene stage. A study of microparticle compositions and of volcanic indicators (Zn, H2SO4), shows that the high observed crustal input is not due to enhanced volcanism, but is rather of continental eolian origin. For the first time, the ionic balance along a deep ice core is established, mainly used in discussing the evolution of the Cl to Na ratio over central East Antarctica with changing climatic conditions: the presence of relatively high amounts of Na2SO4 in the marine aerosol at the Vostok site during the Holocene is demonstrated. Comparison with the Dome C (74°39′S, 124°10′E, 3040 m a.s.l.) results confirms the chronology of the major events: (i) maximum terrestrial input around the last glacial maximum (～18 ka BP); (ii) end of the high continental flux over Antarctica near 13 ka BP; (iii) marine input varying in an opposing manner to isotopic fluctuations with rather high concentrations beginning to decrease when isotopic values increase and reaching Holocene values at the end of the transition between cold and warmer climate conditions. Detailed comparison with results provided by deep ice cores from other sites which are probably more influenced by oceanic air masses seems to indicate that most of the aerosol reaching central East Antarctica travel over large distance probably at rather high altitude through the troposphere. We can consider that central East Antarctica is well representative of the upper part of the troposphere (higher than i.e., 3000 m) and should, therefore, provide valuable data for global and Antarctic paleoclimatological models.  相似文献   

9.
Much work has gone into deciphering the causes of the large scale glacial/interglacial variations in the climate system over the last 900 000 years. While variations on the 41 thousand year (ky) and 23 ky time scales seem to be linearly linked to the variations in the distribution of solar radiation at the top of the atmosphere, Milankovitch solar radiation variations, the causes of the dominant 100 ky cycle in the geologic record are still unknown. One of the aspects of this cycle that is not well understood is how large scale ice sheet growth is initiated. Here we describe the mechanisms by which large scale ice sheet growth may have been initiated by the changes in the seasonal and latitudinal distribution of solar radiation over the past 160 ky. This is done through the use of a coupled energy balance climate-thermodynamic sea ice model that includes a hydrologic cycle which computes precipitation, and a land surface energy balance which determines the net accumulation of snow and ice. Results indicate that the initiation of ice sheet growth is possible during times of extremely low summer solstice solar radiation as a result of a large decrease in ablation during the critical melt season.  相似文献   

10.
Starting from the standpoint that there are seasonal differences of climate variations on both global and local level, the authors of this paper had focused on analyzing climatologic parameters in winter months. The trends of several important parameters were detected, with temperature and precipitation having increasing, but number of ice days and snow cover having decreasing trends. Spectral analysis showed repetitive nature of climatologic parameters, some of them having the same or similar periods of about 6 to 7 years, 10 to 12 or 17.5 years, and 22 to 24 years. The precipitation has periodicity of 8 and 14 years. Further analysis of the underlying structure of the data by principal component analysis detected three easily explained dimensions: Temperature-Snow, Precipitation-Cyclone and Spring-in-Winter dimension. The spectral analysis of three virtual variables obtained by principal component analysis confirmed good agreement of original variables with the virtual dimensions.  相似文献   

11.
利用常规地面和高空观测资料及欧洲中心ERA-5再分析数据,对2021年12月25—27日（21·12）、2022年2月21—23日（22·02）发生在湖南的两次暴雪过程进行诊断分析。两次暴雪过程有强度大、影响范围广,暴雪落区较为重合的特点。两次暴雪过程也表现出明显差异,21·12过程的累计降雪量小于22·02过程,但21·12以干雪为主,22·02以湿雪为主。分析差异的成因发现：（1）22·02过程水汽辐合强度强、延伸高度高、厚度厚,动力条件由南支槽和低涡提供;21·12过程水汽条件相对弱,动力条件由冷锋强迫抬升提供。（2）21·12过程冷空气从低层南下,云中冰相粒子比例大,温度层结满足干雪条件;22·02过程中层气温下降,云中冰相粒子与水相粒子共存,地面气温在0℃以上,故以湿雪为主。  相似文献   

12.
ISOTOPE RECORDS FROM MONGOLIAN AND ALPINE ICE CORES AS CLIMATE INDICATORS   总被引：3，自引：0，他引：3  
The link between long term changes in the isotopic composition of precipitation and surface air temperature at a given location is of exceptional importance for paleoclimatic studies, as ahs been demonstrated by many recent publications based on the isotope records from polar ice cores. By means of direct comparison with instrumental data, this paper evaluates the potential of the deuterium and oxygen-18 records from two continental glaciers for monitoring climatic trends. The isotopic data presented characterize climatically contrasted enviroments. The records from the Swiss glacier show distinct seasonal variations. Oxygen-18 is fairly well correlated with the instrumental record of atmospheric temperature; the seasonal differences in deuterium excess reflect nearness to the oceanic moisture source. By contrast, the isotope data from the Mongolian site show poor correlation with atmospheric temperature. The seasonal variations in deuterium excess, with higher values during summer time, indicate that precipitation largely originates from re-evaporated continental moisture sources. In both cases however, the correlation with temperature is significantly improved by the elimination of values derived from years where major changes in seasonal distribution and/or snow loss obviously have occurred, thereby distoring the isotopic ratios for that particular year. Depending on the site selected for study, the stable isotope composition of ice cores should therefore be viewed not only as a proxy for atmospheric temperature, but also as an additional hydrometeorological parameter and source indicator for atmospheric moisture.  相似文献   

13.
 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   

14.
Three east Antarctic ice cores (Dome B, EPICA-Dome C and Komsomolskaia) give evidence for a uniform dust input to the polar plateau during the last glacial maximum (LGM)/Holocene transition (20 to 10 kyr BP) and the 87Sr/86Sr versus 143Nd/144Nd isotopic signature of the mineral particles highlights a common provenance from southern South America at that time. However, the size distribution of dust from the three ice cores highlights important differences within the east Antarctic during the LGM and shows clearly opposite regional trends during the climatic transition. Between Dome B and Dome C the timing of these changes is also different. A geographical diversity also arises from the different phasing of the short-term (multi-secular scale) dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes. We hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway, either in terms of horizontal trajectory or in altitude of transport. Such mechanism is supported also by the dust size changes observed during a volcanic event recorded in Vostok ice. Ice core dust size data suggest preferential upper air subsidence over the EDC-KMS region and easier penetration of relatively lower air masses to the DB area during the LGM. At the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward. The scenario proposed, supported also by the LGM/Holocene regional changes of snow accumulation, likely operates even at sub-millennial time scale.  相似文献   

15.
Impact of snow initialization on sub-seasonal forecasts   总被引：2，自引：1，他引：1  
The influence of the snowpack on wintertime atmospheric teleconnections has received renewed attention in recent years, partially for its potential impact on seasonal predictability. Many observational and model studies have indicated that the autumn Eurasian snow cover in particular, influences circulation patterns over the North Pacific and North Atlantic. We have performed a suite of coupled atmosphere-ocean simulations with the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast system to investigate the impact of accurate snow initialisation. Pairs of 2-month ensemble forecasts were started every 15 days from the 15th of October through the 1st of December in the years 2004–2009, with either realistic initialization of snow variables based on re-analyses, or else with “scrambled” snow initial conditions from an alternate autumn date and year. Initially, in the first 15 days, the presence of a thicker snowpack cools surface temperature over the continental land masses of Eurasia and North America. At a longer lead of 30-day, it causes a warming over the Arctic and the high latitudes of Eurasia due to an intensification and westward expansion of the Siberian High. It also causes a cooling over the mid-latitudes of Eurasia, and lowers sea level pressures over the Arctic. This “warm Arctic—cold continent” difference means that the forecasts of near-surface temperature with the more realistic snow initialization are in closer agreement with re-analyses, reducing a cold model bias over the Arctic and a warm model bias over mid-latitudes. The impact of realistic snow initialization upon the forecast skill in snow depth and near-surface temperature is estimated for various lead times. Following a modest skill improvement in the first 15 days over snow-covered land, we also find a forecast skill improvement up to the 30-day lead time over parts of the Arctic and the Northern Pacific, which can be attributed to the realistic snow initialization over the land masses.  相似文献   

16.
长江流域水分收支以及再分析资料可用性分析   总被引：9，自引：0，他引：9  
赵瑞霞  吴国雄 《气象学报》2007,65(3):416-427
首先利用实测资料定量计算了长江流域水分收支的各分量,包括降水、径流、蒸发、水汽辐合等,分析其季节循环、年际变化以及线性趋势变化。结果表明,多年平均该流域是水汽汇区,主要来自平均流输送造成的水汽辐合,而与天气过程密切相关的瞬变波则主要造成流域的水汽辐散。蒸发所占比例接近于径流,对流域水分循环十分重要。大部分要素的季节变化和年际变化都很大,只有蒸发和大气含水量的年际变化较小。降水和平均流输送造成的水汽辐合一般在6月达到年内最大,12月达到年内最小,而径流和大气含水量则一般滞后1个月于7月达到年内最大,1月降为年内最小。1958—1983年,夏半年降水略微增加,冬半年略微减少,各月实测径流为弱的增长趋势,但均不显著,年平均蒸发亦无显著的趋势变化。然后将实测资料同ECMWF及NCEP/NCAR再分析资料作进一步对比分析,以检验两套再分析资料对长江流域水分循环的描述能力。在量值上,NCEP/NCAR再分析资料中的降水、蒸发、径流均比实测偏大很多,大气含水量及由平均流输送所造成的水汽辐合则偏小很多;ECMWF再分析资料中的降水量、径流量基本上与实测接近,蒸发量偏大,大气含水量及由平均流输送所造成的水汽辐合偏小,但比NCEP/NCAR再分析资料要接近实测。另外,该两套再分析资料均可以较好地描述长江流域水分收支的季节循环和年际变化,而且同样是ECMWF再分析资料与实测资料的一致性更好。但是两套再分析资料在1958—1983年均存在十分夸张的线性趋势变化,尤其是ECMWF再分析资料。  相似文献   

17.
Extraordinary blowing snow transport events in East Antarctica   总被引：1，自引：1，他引：0  
In the convergence slope/coastal areas of Antarctica, a large fraction of snow is continuously eroded and exported by wind to the atmosphere and into the ocean. Snow transport observations from instruments and satellite images were acquired at the wind convergence zone of Terra Nova Bay (East Antarctica) throughout 2006 and 2007. Snow transport features are well-distinguished in satellite images and can extend vertically up to 200 m as first-order quantitatively estimated by driftometer sensor FlowCapt?. Maximum snow transportation occurs in the fall and winter seasons. Snow transportation (drift/blowing) was recorded for ~80% of the time, and 20% of time recorded, the flux is >10?2 kg m?2 s?1 with particle density increasing with height. Cumulative snow transportation is ~4 orders of magnitude higher than snow precipitation at the site. An increase in wind speed and transportation (~30%) was observed in 2007, which is in agreement with a reduction in observed snow accumulation. Extensive presence of ablation surface (blue ice and wind crust) upwind and downwind of the measurement site suggest that the combine processes of blowing snow sublimation and snow transport remove up to 50% of the precipitation in the coastal and slope convergence area. These phenomena represent a major negative effect on the snow accumulation, and they are not sufficiently taken into account in studies of surface mass balance. The observed wind-driven ablation explains the inconsistency between atmospheric model precipitation and measured snow accumulation value.  相似文献   

18.
Future climate in the Pacific Northwest   总被引：4，自引：2，他引：2  
Climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and twentieth century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1°C to 0.6°C (0.2°F to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1% to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of twenty-first century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as twentieth century values (20 cm, 8″) or as large as 1.3 m (50″).  相似文献   

19.
Global climate models predict that terrestrial northern high-latitude snow conditions will change substantially over the twenty-first century. Results from a Community Climate System Model simulation of twentieth and twenty-first (SRES A1B scenario) century climate show increased winter snowfall (+10–40%), altered maximum snow depth (?5 ± 6 cm), and a shortened snow-season (?14 ± 7 days in spring, +20 ± 9 days in autumn). By conducting a series of prescribed snow experiments with the Community Land Model, we isolate how trends in snowfall, snow depth, and snow-season length affect soil temperature trends. Increasing snowfall, by countering the snowpack-shallowing influence of warmer winters and shorter snow seasons, is effectively a soil warming agent, accounting for 10–30% of total soil warming at 1 m depth and ~16% of the simulated twenty-first century decline in near-surface permafrost extent. A shortening snow season enhances soil warming due to increased solar absorption whereas a shallowing snowpack mitigates soil warming due to weaker winter insulation from cold atmospheric air. Snowpack deepening has comparatively less impact due to saturation of snow insulative capacity at deeper snow depths. Snow depth and snow-season length trends tend to be positively related, but their effects on soil temperature are opposing. Consequently, on the century timescale the net change in snow state can either amplify or mitigate soil warming. Snow state changes explain less than 25% of total soil temperature change by 2100. However, for the latter half of twentieth century, snow state variations account for as much as 50–100% of total soil temperature variations.  相似文献   

20.
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   

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