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1.
Both observational and numerical studies demonstrate the sensitivity of the atmosphere to variations in the extent and mass of snow cover. There is therefore a need for simple but realistic snow parameterizations in forecast and climate models. A new snow hydrology scheme has recently been developed at Météo-France for use in the ARPEGE climate model and has been successfully tested against local field measurements in stand-alone experiments. This study describes the global validation of the parameterization in a 3-year integration for the present-day climate within the T42L30 version of ARPEGE. Results are compared with those from a control simulation and with available observed climatologies, in order to assess the impact of the new snow parameterization on the simulated surface climate. The seasonal cycle of the Northern Hemisphere snow cover is clearly improved when using the new scheme. The snow pack is still slightly overestimated in winter, but its poleward retreat is better reproduced during the melting season. As a consequence, the modified GCM performs well in simulating the springtime continental heating, which may play a strong role in the simulation of the Asian summer monsoon. 相似文献
2.
Simulated variability and trends in Northern Hemisphere seasonal snow cover are analyzed in large ensembles of climate integrations of the National Center for Atmospheric Research’s Community Earth System Model. Two 40-member ensembles driven by historical radiative forcings are generated, one coupled to a dynamical ocean and the other driven by observed sea surface temperatures (SSTs) over the period 1981–2010. The simulations reproduce many aspects of the observed climatology and variability of snow cover extent as characterized by the NOAA snow chart climate data record. Major features of the simulated snow water equivalent (SWE) also agree with observations (GlobSnow Northern Hemisphere SWE data record), although with a lesser degree of fidelity. Ensemble spread in the climate response quantifies the impact of natural climate variability in the presence and absence of coupling to the ocean. Both coupled and uncoupled ensembles indicate an overall decrease in springtime snow cover that is consistent with observations, although springtime trends in most climate realizations are weaker than observed. In the coupled ensemble, a tendency towards excessive warming in wintertime leads to a strong wintertime snow cover loss that is not found in observations. The wintertime warming bias and snow cover reduction trends are reduced in the uncoupled ensemble with observed SSTs. Natural climate variability generates widely different regional patterns of snow trends across realizations; these patterns are related in an intuitive way to temperature, precipitation and circulation trends in individual realizations. In particular, regional snow loss over North America in individual realizations is strongly influenced by North Pacific SST trends (manifested as Pacific Decadal Oscillation variability) and by sea level pressure trends in the North Pacific/North Atlantic sectors. 相似文献
3.
The role of terrestrial snow cover in the climate system 总被引：2，自引：0，他引：2
Steve Vavrus 《Climate Dynamics》2007,29(1):73-88
Snow cover is known to exert a strong influence on climate, but quantifying its impact is difficult. This study investigates
the global impact of terrestrial snow cover through a pair of GCM simulations run with prognostic snow cover and with all
snow cover on land eliminated (NOSNOWCOVER). In this experiment all snowfall over land was converted into its liquid–water
equivalent upon reaching the surface. Compared with the control run, NOSNOWCOVER produces mean-annual surface air temperatures
up to 5 K higher over northern North America and Eurasia and 8–10 K greater during winter. The globally averaged warming of
0.8 K is one-third as large as the model’s response to 2 × CO2 forcing. The pronounced surface heating propagates throughout the troposphere, causing changes in surface and upper-air circulation
patterns. Despite the large atmospheric warming, the absence of an insulating snow pack causes soil temperatures in NOSNOWCOVER
to fall throughout northern Asia and Canada, including extreme wintertime cooling of over 20 K in Siberia and a 70% increase
in permafrost area. The absence of snow melt water also affects extratropical surface hydrology, causing significantly drier
upper-layer soils and dramatic changes in the annual cycle of runoff. Removing snow cover also drastically affects extreme
weather. Extreme cold-air outbreaks (CAOs)—defined relative to the control climatology—essentially disappear in NOSNOWCOVER.
The loss of CAOs appears to stem from both the local effects of eliminating snow cover in mid-latitudes and a remote effect
over source regions in the Arctic, where −40°C air masses are no longer able to form. 相似文献
4.
Actual and insolation-weighted Northern Hemisphere snow cover and sea ice are binned by latitude bands for the years 1973–2002. Antarctic sea-ice is also analyzed for the years 1980–2002. The use of insolation weighting provides an improved estimate of the radiative feedbacks of snow cover and sea-ice into the atmosphere. One conclusion of our assessment is that while a decrease in both areal and insolation-weighted values have occurred, the data does not show a monotonic decrease of either Arctic sea-ice or Northern Hemisphere snow cover. If Arctic perennial sea-ice is decreasing since the total reduction in areal coverage is relatively small, a large portion of it is being replenished each year such that its radiative feedback to the atmosphere is muted. Antarctic sea-ice areal cover shows no significant long-term trend, while there is a slight decrease in the insolation-weighted values for the period 1980–2002. From the early 1990s to 2001, there was a slight increase in both values. The comparison of general circulation model simulations of changes over the last several decades to observed changes in insolation-weighted sea-ice and snow cover should be a priority research topic. 相似文献
5.
Snow cover fraction (SCF) has a significant influence on the surface albedo and thus on the radiation balance and surface
climate. Long-term three dimensional simulations with general circulation models (GCMs) show that the SCF greatly affects
the climate in the Northern Hemisphere. By means of both ground observations and remotely sensed data, several deficiencies
in the SCF simulated by the current ECHAM4 GCM were identified: over mountainous areas a substantial overestimation in the
SCF was found whereas flat areas showed a distinctly underestimated SCF. This work proposes a new parametrization of the SCF
for use in GCMs. Evaluations illustrate that it is beneficial to distinguish between the following three terrains: (1) flat,
non-forested areas, (2) mountainous regions and (3) forests. The modified SCF parametrization for flat, non-forested areas
was derived by using global datasets of ground-based snow depth and remote sensing observations of snow cover data. A 3-dimensional
ECHAM4 simulation showed that this modification raises the SCF by up to approximately 20%, mainly in areas with a relatively
thin snow cover. The comparison between remotely sensed and simulated mean monthly surface albedo revealed a significant overestimation
of the surface albedo in snow-covered mountainous areas. An extension of the current SCF parametrization in ECHAM4 to take
into account mountain effects, based on the French climate model Arpège, yielded a close agreement with satellite-derived
surface albedo. The adoption of the submodel for snow albedo, as used in the Canadian Land Surface Scheme (CLASS), combined
with a newly developed simple snow interception model, demonstrated the ability to capture the main physical processes of
snow-covered canopies, including the albedo. The validation of the new parametrization with Boreal Ecosystem-Atmosphere Study
(BOREAS) field data showed that the modification is appropriate to capture the main features of the albedo over snow-covered
forests during and after heavy snowfall events. Furthermore, the proposed modification has a beneficial impact on the delayed
snow melt in spring, a well-known problem in many current GCMs: The simulated surface albedo over the boreal forests decreases
by approximately 0.1 during winter and spring, which is in better agreement with ground-based observations. This induces a
significant rise in the surface temperature over extended parts of Eurasia and North America in late spring, which subsequently
yields a faster snowmelt and an accelerated retreat of the snow line.
Received: 28 April 2000 / Accepted: 18 December 2000 相似文献
6.
积雪分布及其对中国气候影响的研究进展 总被引：12，自引：0，他引：12
对北半球不同地区的积雪分布状况、积雪异常影响中国气候的事实以及影响机理等问题的研究成果进行了较系统的回顾与总结。青藏高原、蒙古高原、欧洲阿尔卑斯山脉及北美中西部是北半球积雪分布的关键区,其中青藏高原是北半球积雪异常变化最强烈的区域。中国积雪分布范围广泛,其中新疆、东北和青藏高原是3个大值区。总体来看,北半球积雪有减少的趋势,而中国积雪却有弱的增加趋势。冬、春季高原积雪与欧亚积雪对中国夏季降水的影响是相反的。积雪影响中国气候的机理解释为：冬季积雪反照率效应起主要作用,春夏季积雪水文效应起主要作用。积雪被视为中国短期气候预测的一个重要物理因子,继续加强该领域的研究对于提高中国短期气候预测的准确率将有重要意义。 相似文献
7.
Ice-free glacial northern Asia due to dust deposition on snow 总被引：3，自引：0，他引：3
During the Last Glacial Maximum (LGM, 21 kyr BP), no large ice sheets were present in northern Asia, while northern Europe and North America (except Alaska) were heavily glaciated. We use a general circulation model with high regional resolution and a new parameterization of snow albedo to show that the ice-free conditions in northern Asia during the LGM are favoured by strong glacial dust deposition on the seasonal snow cover. Our climate model simulations indicate that mineral dust deposition on the snow surface leads to low snow albedo during the melt season. This, in turn, caused enhanced snow melt and therefore favoured snow-free peak summer conditions over almost the entire Asian continent during the LGM, whereas perennial snow cover is simulated over a large part of eastern Siberia when glacial dust deposition is not taken into account. 相似文献
8.
Bhogendra Mishra Mukand S. Babel Nitin K. Tripathi 《Theoretical and Applied Climatology》2014,116(3-4):681-694
Various remote sensing products and observed data sets were used to determine spatial and temporal trends in climatic variables and their relationship with snow cover area in the higher Himalayas, Nepal. The remote sensing techniques can detect spatial as well as temporal patterns in temperature and snow cover across the inaccessible terrain. Non-parametric methods (i.e. the Mann–Kendall method and Sen's slope) were used to identify trends in climatic variables. Increasing trends in temperature, approximately by 0.03 to 0.08 °C year?1 based on the station data in different season, and mixed trends in seasonal precipitation were found for the studied basin. The accuracy of MOD10A1 snow cover and fractional snow cover in the Kaligandaki Basin was assessed with respect to the Advanced Spaceborne Thermal Emission and Reflection Radiometer-based snow cover area. With increasing trends in winter and spring temperature and decreasing trends in precipitation, a significant negative trend in snow cover area during these seasons was also identified. Results indicate the possible impact of global warming on precipitation and snow cover area in the higher mountainous area. Similar investigations in other regions of Himalayas are warranted to further strengthen the understanding of impact of climate change on hydrology and water resources and extreme hydrologic events. 相似文献
9.
In this research, we studied the effects of black carbon (BC) aerosol radiative forcing on seasonal variation in the Northern Hemisphere (NH) using numerical simulations with the NASA finite-volume General Circulation Model (fvGCM) forced with monthly varying three-dimensional aerosol distributions from the Goddard Ozone Chemistry Aerosol Radiation and Transport Model (GOCART). The results show that atmospheric warming due to black carbon aerosols subsequently warm the atmosphere and land surfaces, especially those over Eurasia. As a result, the snow depth in Eurasia was greatly reduced in late winter and spring, and the reduction in snow cover decreased the surface albedo. Our surface energy balance analysis shows that the surface warming due to aerosol absorption causes early snow melting and further increases surface-atmosphere warming through snow/ice albedo feedback. Therefore, BC aerosol forcing may be an important factor affecting the snow/ice albedo in the NH. 相似文献
10.
A monthly snow accumulation and melt model is used with gridded monthly temperature and precipitation data for the Northern Hemisphere to generate time series of March snow-covered area (SCA) for the period 1905 through 2002. The time series of estimated SCA for March is verified by comparison with previously published time series of SCA for the Northern Hemisphere. The time series of estimated Northern Hemisphere March SCA shows a substantial decrease since about 1970, and this decrease corresponds to an increase in mean winter Northern Hemisphere temperature. The increase in winter temperature has caused a decrease in the fraction of precipitation that occurs as snow and an increase in snowmelt for some parts of the Northern Hemisphere, particularly the mid-latitudes, thus reducing snow packs and March SCA. In addition, the increase in winter temperature and the decreases in SCA appear to be associated with a contraction of the circumpolar vortex and a poleward movement of storm tracks, resulting in decreased precipitation (and snow) in the low- to mid-latitudes and an increase in precipitation (and snow) in high latitudes. If Northern Hemisphere winter temperatures continue to warm as they have since the 1970s, then March SCA will likely continue to decrease. 相似文献
11.
A deforestation experiment is performed using the Laboratoire de Meteorologie Dynamique Atmospheric General Circulation Model (LMD GCM) to determine the climatic role of the largest vegetation formation in the Northern Hemisphere, localized mostly north of latitude 45°N, which is called the temperate and boreal forest. For this purpose, an iterative albedo scheme based on vegetation type, snow age, snowfall rate and area of snow cover, is developed for snow-covered surfaces. The results show a cooling of Northern Hemisphere soil and an increase in the snow cover when the forest is removed, as found by previous similar experiments.In our study this cooling is related to different causes, depending on the season. It is linked to modifications in the soil radiative properties, like surface albedo, due to the disappearance of forest, and consequently, to a greater exposure of the snow-covered soil underneath. It is also related to alterations in the hydrological cycle, observed mainly in summer and autumn at middle latitudes. The model shows a strong sensitivity to the coupled surface albedo — soil temperature — fractional snow cover response in the spring. A later and longer snowmelt season is also detected.This study adds to our understanding of climatic variation on longer time scales, since it is widely accepted that the formation and disappearance of different vegetation formations is closely related to climatic evolution patterns, in particular on the time scale of the glacial oscillations. 相似文献
12.
春季欧亚大陆积雪对春夏季南北半球大气质量交换的可能影响 总被引：2，自引：0，他引：2
本文基于春季欧亚雪盖资料与大气再分析资料的奇异值分解(SVD)分析结果,结合数值试验,研究了春季欧亚大陆积雪变化与春、夏季南北半球大气质量交换的联系。研究表明,当春季欧亚积雪异常偏多时,同期欧亚大陆中高纬大范围地区的地面气温异常偏低,这种冷却效应可能持续至夏季,同时,冷空气的堆积造成了欧亚大陆地表气压(气柱大气质量)的增加,并且对应了夏季北半球大气总质量的异常上升,而南半球大气质量却明显下降。分析发现,春季欧亚积雪异常与夏季南北半球际大气质量涛动存在显著的滞后相关,而且前者还与同期及后期包括索马里急流和对流层上部80°E~120°E区域高空急流在内的多处越赤道气流变化联系密切。从数值模拟结果分析发现,以改变春季初始积雪状况作为驱动,欧亚大陆中高纬地区的低层大气环流出现了显著响应,即当积雪增加时,同期及其后夏季地面气温显著降低,并且冷异常区域对应着气柱质量的异常升高。 相似文献
13.
14.
Robert J Oglesby 《Climate Dynamics》1990,4(4):219-235
We present results from numerical experiments made with a GCM, the NCAR CCM1, that were designed to estimate the annual balance between snow-fall accumulation and ablation for geographically important land regions for a variety of conditions. We also attempt to assess the reliability of these results by investigating model sensitivity to changes in prescribed physical parameters. Experiments were run with an initial imposition of 1 m of (midwinter) snowcover over all northern hemisphere land points. Over Alaska, western Canada, Siberia, and the Tibetan Plateau the model tended to retain this snow cover through the summer and in some cases increase its depth as well. We define these regions as glaciation sensitive and note some correspondence between them and source regions for the Pleistocene ice sheets. An experiment with greatly reduced CO2 (100 ppm) showed a tendency towards spontaneous glaciation, i.e., the model remained snow-covered throughout the summer over the same geographic regions noted above. With 200 ppm CO2 (roughly equal to values at the last glacial maximum), snow cover over these regions did not quite survive the summer on a consistent basis. Combining 200 ppm CO2 and 1 m of initial northern hemisphere snow cover yielded glaciation-sensitive conditions, agreeing remarkably well with locations undergoing glaciation during the Pleistocene. To assess the reliability of these results, we have determined minimal model uncertainty by varying two of the empirical coefficients in the model within physically plausible ranges. In one case surface roughness of all ocean gridpoints was reduced by an order of magnitude, leading to local 10% reductions in precipitation (snowfall), a change hard to distinguish from inherent model variability. In the other case, the fraction of a land grid square assumed to be occupied by snow cover for albedo purposes was varied from one-half to unity. Large changes occurred in the degree of summer melting, and in some cases the sign of the net balance changed as fractional snow cover was changed. We conclude that the model may be able to reveal regions sensitive to glaciation, but that it cannot yield a reliable quantitative computation of the magnitude of the net snow accumulation that can be implicitly or explicitly integrated through time.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dilmenil 相似文献
15.
The potential impact of climate change on seasonal snow in New Zealand: part I—an analysis using 12 GCMs 总被引：1，自引：0，他引：1
J. Hendrikx E. ? Hreinsson M. P. Clark A. B. Mullan 《Theoretical and Applied Climatology》2012,110(4):607-618
Seasonal snow directly affects New Zealand??s economy through the energy, agriculture and tourism sectors. In New Zealand, little is known about the long-term variability of the snow cover and the expected impacts of climate change on snow cover. The lack of systematic historical snow observations in New Zealand means that information on interannual variability, trends and projections of future seasonal snow must be generated using simulation models. We use a temperature index snow model to calculate the accumulation and ablation of the current (1980?C1999) snowpack for more than 37,000 third-order river basins with 100?m contour intervals, resulting in over 200,000 individual model elements in New Zealand. Using this model, which captures the gross features of snow under the current climate, we assess the range of likely effects of climate change on seasonal snow in New Zealand using downscaled temperature and precipitation changes from the middle of the road (A1B) climate change projections from 12 general circulation models (GCMs). For each of the 12 GCMs, we consider two future time periods 2030?C2049 (mid-point reference 2040) and 2080?C2099 (mid-point reference 2090). These future time periods are compared to simulations of current, 1980?C1999 (mid-point reference 1990), seasonal snow. Our results show that on average at a national scale, at nearly all elevations, the 2040s and 2090s result in a decrease in snow as described by all of our summary statistics: snow duration, percentage of precipitation that is snow and peak snow accumulation in each year. This decrease in snow is more marked at elevations below 1,000?m but is evident at all but the very highest elevations. Relative to snow simulations for average peak snow accumulation for the present, we observe that by the 2040s, depending on the GCM used, there is a reduction of between 3 and 44?% at 1,000?m, and an increase of 8?% through to a reduction of 22?% at 2,000?m. By the 2090s, the average reduction is greater, with a decrease of between 32 and 79?% at 1,000?m and between 6 and 51?% at 2,000?m. More substantial reductions are observed below these elevations. When we consider the elevation where snow duration exceeds 3?months, we see a rise in this elevation from 1,550?m in the 1990s to between 1,550 and 1,750?m by the 2040s and 1,700 and 2,000?m by the 2090s, depending on the GCM used. The results of this work are consistent with our understanding of snow processes in general and with work from other similar mid-latitude locations. 相似文献
16.
Annual cycles of monthly albedos simulated with a general circulation model (GCM) are compared with surface observations.
The data observed at 35 stations are retrieved from the Global Energy Balance Archive (GEBA) and drawn from the soil moisture
and meteorological observations in the former Soviet Union. The model data are obtained with the ECHAM4 GCM in a ten-year
simulation of the present-day climate at T106 resolution. The model calculated albedo values are modified before they are
compared with the surface observations: They are interpolated to the stations and adjusted to account for altitude differences
and fractional forest area. During the snow-free period, the model underestimates the albedo by up to 0.05 at the stations
(with values between 0.2 and 0.25 measured over short grass) because the albedo for grassland is too low in the model. During
the period with seasonal snow cover, the model underestimates the albedo by up to 0.2 at stations in Russia, Scandinavia and
Canada, which experience severe winters. This underestimation is due to an oversimplified parameterization of the snow covered
grid fraction and an inadequate linear relation between snow albedo and temperature. The derivative of albedo with respect
to the forest fraction implemented in ECHAM is in line with the observations, although a small overestimation of the model’s
gradient has been detected.
Received: 3 July 1998 / Accepted: 24 December 1998 相似文献
17.
An empirical formula to compute snow cover fraction in GCMs 总被引：10，自引：0，他引：10
There exists great uncertainty in parameterizing snow cover fraction in most general circulation models (GCMs) using various empirical formulae, which has great influence on the performance of GCMs. This work reviews the commonly used relationships between region-averaged snow depth (or snow water equivalent) and snow cover extent (or fraction) and suggests a new empirical formula to compute snow cover fraction, which only depends on the domain-averaged snow depth, for GCMs with different horizontal resolution. The new empirical formula is deduced based on the 10-yr (1978-1987) 0.5°× 0.5° weekly snow depth data of the scanning multichannel microwave radiometer (SMMR) driven from the Nimbus-7 Satellite. Its validation to estimate snow cover for various GCM resolutions was tested using the climatology of NOAA satellite-observed snow cover. 相似文献
18.
CCM3模式中LSM积雪方案的改进研究(Ⅰ):修改方案介绍及其单点试验 总被引：4，自引：3，他引：1
为了改进美国NCARCCM3全球模式中LSM陆面模型中的积雪方案的模拟效果,在Sun等[1]SAST积雪模型的基础上,作了部分修改后,加进CCM3模式LSM模型中.该方案根据格点区域平均积雪深度的不同,把地面雪盖划分为1到3层不等,能在积雪表层和中间层更好地描述温度的日变化和季节变化;较详细地考虑了雪的热传导、太阳辐射的穿透吸收、雪的融化、液态水的储存、渗透和再冻结等积雪内部的主要物理过程;根据Nimbus-7卫星实测雪深资料修改了积雪覆盖度和雪面反照率的计算方案.利用前苏联6个台站1978-1983年的实测积雪资料和大气强迫数据,进行了单点模拟试验,结果表明,新的积雪参数化方案能够较好地再现积雪深度和雪水当量的逐日和季节变化特征,部分提高了积雪参数化方案对积雪的模拟能力. 相似文献
19.
The albedo of snow for different cloudiness conditions is an important parameter in the Earth's radiation budget analysis and in the study of snowpack's thermal conditions. In this study an efficient approximate method is derived to calculate the incident spectral solar flux and snow-cover albedo in terms of different atmospheric, cloud, and snow parameters. The global flux under partially cloudy skies is expressed in terms of the clear sky flux and a coefficient which models the effect of scattering and absorption by cloud patches and multiple reflections between the cloud base and snowcover. The direct and the diffuse components of the clear sky flux are obtained using the spectral flux outside the atmosphere and the spectral transmission coefficients for absorption and scattering by molecules and aerosols.The spectral snow reflectance model considers both specular surface reflection and volumetric multiple scattering. The surface reflection is calculated by using a crystal-shape-dependent bidirectional reflectance distribution function; the volumetric multiple scattering is calculated by using a crystal-size-dependent approximate solution in the radiative transfer equation. The input parameters to the model are atmospheric precipitable water, ozone content, turbidity, cloud optical thickness, the size and shape of ice crystals of snow and surface pressure. The model yields spectral and integrated solar flux and snow reflectance as a function of solar elevation and fractional cloudcover.The model is illustrated using representative parameters for the Antarctic coastal regions. The albedo for a clear sky depends inversely on the solar elevation. At high elevations the albedo depends primarily upon the grain size; at low elevation the albedo depends on grain size and shape. The gradient of the albedo-elevation curve increases as the grains become larger and faceted. The albedo for a densely overcast sky is a few percent higher than the clear-sky albedo at high elevations. A simple relationship between grain size and the overcast albedo is obtained. For a set of grain size and shape, the albedo as a function of solar elevation and fractional cloud cover is tabulated. 相似文献
20.
Summary Northern Hemisphere monthly mean temperature anomalies during the twentieth century exhibit seasonal differences. To expose
the most significant intermonthly dissimilarities, here we investigate this issue in more details. We show that the trends
significantly differ for the months close to the equinoxes. Using the technique of multidimensional scaling analysis we find
that two underlying attributes are sufficient to acceptably describe the structure of the observed intermonthly dissimilarities.
Namely, these are the monthly sample percentiles around the 30th and the 70th together with the linear trends. We find that
intraannual temperature anomaly dissimilarities statistically depend on the seasonal cycles of the Northern Hemisphere oceanic
heat content, sea ice and snow cover and the Arctic sea ice cover as well as on the seasonality of the chaoticity of the Northern
Hemisphere atmospheric dynamics. We also speculate that the annual cycles of these ocean and cryosphere characteristics statistically
set the pattern for the observed course of linear warming over the calendar months. 相似文献