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1.
以能量平衡方程为基础,考虑太阳短波辐射、大气和地面的长波辐射、潜热、感热传输以及下垫面的热传导等能量之间的平衡,建立了利用常规气象观测资料预测雪面温度和积雪深度变化的融雪模型。利用2009年1—3月以及2009年12月—2010年1月在湖北恩施雷达站的积雪观测数据进行模拟和验证,结果表明：该模型对于雪面温度和积雪深度都有较好的模拟效果。当下垫面导热系数λg〈0.5时,下垫面对雪深的影响很小;当λg≥0.5时,积雪融化速度随λg的增大而加快,说明下垫面的热传导是影响积雪深度变化的主要因素之一。 相似文献
2.
The snow cover extent in mid-high latitude areas of the Northern Hemisphere has significantly declined corresponding to the global warming, especially since the 1970s. Snow-climate feedbacks play a critical role in regulating the global radiation balance and influencing surface heat flux exchange. However, the degree to which snow cover changes affect the radiation budget and energy balance on a regional scale and the difference between snow-climate and land use/cover change (LUCC)-climate feedbacks have been rarely studied. In this paper, we selected Heilongjiang Basin, where the snow cover has changed obviously, as our study area and used the WRF model to simulate the influences of snow cover changes on the surface radiation budget and heat balance. In the scenario simulation, the localized surface parameter data improved the accuracy by 10 % compared with the control group. The spatial and temporal analysis of the surface variables showed that the net surface radiation, sensible heat flux, Bowen ratio, temperature and percentage of snow cover were negatively correlated and that the ground heat flux and latent heat flux were positively correlated with the percentage of snow cover. The spatial analysis also showed that a significant relationship existed between the surface variables and land cover types, which was not obviously as that for snow cover changes. Finally, six typical study areas were selected to quantitatively analyse the influence of land cover types beneath the snow cover on heat absorption and transfer, which showed that when the land was snow covered, the conversion of forest to farmland can dramatically influence the net radiation and other surface variables, whereas the snow-free land showed significantly reduced influence. Furthermore, compared with typical land cover changes, e.g., the conversion of forest into farmland, the influence of snow cover changes on net radiation and sensible heat flux were 60 % higher than that of land cover changes, indicating the importance of snow cover changes in the surface-atmospheric feedback system. 相似文献
3.
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
4.
海-陆-气全球耦合模式能量收支的误差 总被引：4，自引：0，他引：4
通过分析GOALS模式两个版本GOALS 1.1和GOALS 2的能量收支 ,并与观测对比 ,结果表明 :模式模拟的地表净短波辐射通量在高纬地区偏低 ,而净长波辐射通量又偏高 ,导致极地表面温度偏低 ,感热通量在高纬地区为很高的负值。而在陆地上感热加热作用显著偏强 ,使地表有较大的向上净能量给大气 ,引起陆地上有些暖中心也偏强 ,这也解释了模式模拟地表面空气温度场的误差原因。海洋上潜热通量偏低 ,特别是在副热带洋面上偏少更明显。陆地上的欧亚和北美大陆大部分地区潜热通量仍偏低。这也是模式降水在大部分地区偏少的重要原因。两模式大气顶OLR偏低的模拟主要是在中低纬度 ,大气顶净短波辐射通量的模拟在中低纬度虽然与NCEP结果接近 ,但与地球辐射收支试验ERBE资料比较仍偏小较多 ,说明改进中低纬度云 辐射参数化方案对改进全球能量收支的模拟有重要意义。GOALS 2模式中诊断云方案模拟的云量除赤道地区外普遍偏小 ,尤以中纬度为甚 ,造成那里能量收支出现大的误差 ,这表明了更好的云参数化方案的引入是今后模式发展的重要任务之一 相似文献
5.
The energy budget of the two versions of the GOALS model (GOALS-1.1 and GOALS-2) is described and compared to observational estimates.The results illustrate that the simulated surface net shortwave radiation flux is underestimated in the high-latitude regions while the surface net longwave radiation flux is substantially overestimated in that region,which results in the lower surface air temperature (SAT) of the polar region and the stronger negative sensible heat flux in high latitudes.The overestimated sensible heat flux from surface to atmosphere in the continents causes the much warmer SAT centers,which may be the reason for the bias of the model SAT. The bias that the simulated precipitation is less than observation in most regions is closely related to the underestimated latent heat flux over most of the Eurasian Continent and the oceans, especially over the subtropical oceans.It can be seen that the bias in the OLR of the two models lies in low and middle latitudes,where the absorbed solar shortwave radiation flux at the top of the atmosphere is comparable to the NCEP reanalysis,but much less than ERBE data.This indicates that the improvement of cloud-radiation parameterization scheme in low and middle latitudes is of critical importance to the simulation of global energy budget.The simulated cloud cover from the GOALS-2 model with diagnosed cloud scheme is generally less except at equatorial areas, especially in the mid-latitude areas,which causes the large bias of energy budget there.It is suggested that the refinement of cloud parameterization is one of the most important tasks in the model's future development. 相似文献
6.
Summary Strong stable layers are a common occurrence during western Colorado's winter. Analysis of radiosonde observations indicate wintertime boundary layer heights are near 500 m. The terrain in this region consists of mountains that rise approximately 1500–2000 m above the ground to the east, providing an effective blocking barrier. An experiment is described to observe upwelling and downwelling, longwave and shortwave radiative fluxes at two sites in western Colorado during January and February 1992, for combinations of clear, cloudy, snow covered, and bare ground periods. Analysis of the observations and the surface energy budget for typical Bowen ratios provides a better understanding of the role of radiation in maintaining and destroying stable layers.During the day, the surface received a net gain of energy from radiation, while at night there was a net loss. Over snow, the 24-hour net radiative flux was small and either positive or negative. Over bare soil, the 24-hour net radiative flux was positive but still small. There is little difference in the net radiative flux between clear and cloudy days; the reduction of the incident solar flux by clouds is nearly compensated by the hindering of the longwave cooling. The cumulative effects of the 24-hour net radiative flux were negative over snow early in the experiment. The 24-hour values shifted to near zero as the snow albedo decreased and were positive for bare ground.If the daytime net radiative flux is partitioned into sensible and latent heat flux using typical Bowen ratios, the daytime sensible heat available for destroying boundary layers is small for the low solar angles of the winter season. With a Bowen ratio of 0.5, the daytime sensible heat flux available is only 0.3 to 1.2 MJ m–2 over a snow surface and 1.4 to 2.3 MJ m–2 over soil. These heat fluxes will not build a deep enough boundary layer to break a typical wintertime inversion. The 24-hour sensible heat flux was negative at both sites for the entire experiment with this Bowen ratio.The radiation observations and the use of typical Bowen ratios lead to the conclusion that the net radiation will sustain or strengthen a stable atmosphere in the winter season in western Colorado. Analysis of the radiosonde observations confirm this result as the boundary layer depths were less than 500 m early in the experiment and grew to only 700 m later in the experiment.With 12 Figures 相似文献
7.
A physically-based multi-layer snow model Snow-Atmosphere-Soil-Transfer scheme(SAST)and a land surface model Biosphere-Atmosphere Transfer Scheme(BATS)were employed to investigate how boreal forests influence snow accumulation and ablation under the canopy.Mass balance and energetics of snow beneath a Scots pine canopy in Finland at different stages of the 2003-2004 and 2004 2005 snow seasons are analyzed.For the fairly dense Scots pine forest,drop-off of the canopy-intercepted snow contributes,in some cases,twice as much to the underlying snowpack as the direct throughfall of snow.During early winter snow melting,downward turbulent sensible and condensation heat fluxes play a dominant role together with downward net longwave radiation.In the final stage of snow ablation in middle spring,downward net all- wave radiation dominates the snow melting.Although the downward sensible heat flux is comparable to the net solar radiation during this period,evaporative cooling of the melting snow surface makes the turbulent heat flux weaker than net radiation.Sensitivities of snow processes to leaf area index(LAI)indicate that a denser canopy speeds up early winter snowmelt,but also suppresses melting later in the snow season. Higher LAI increases the interception of snowfall,therefore reduces snow accumulation under the canopy during the snow season;this effect and the enhancement of downward longwave radiation by denser foliage outweighs the increased attenuation of solar radiation,resulting in earlier snow ablation under a denser canopy.The difference in sensitivities to LAI in two snow seasons implies that the impact of canopy density on the underlying snowpack is modulated by interannual variations of climate regimes. 相似文献
8.
D. Melas T. Persson H. De Bruin S.-E. Gryning E. Batchvarova C. Zerefos 《Theoretical and Applied Climatology》2001,70(1-4):105-116
Summary A mesoscale numerical model, incorporating a land-surface scheme based on Deardorffs’ approach, is used to study the diurnal
variation of the boundary layer structure and surface fluxes during four consecutive days with air temperatures well below
zero, snow covered ground and changing synoptic forcing. Model results are evaluated against in-situ measurements performed
during the WINTEX field campaign held in Sodankyl?, Northern Finland in March 1997. The results show that the land-surface
parameterization employed in the mesoscale model is not able to reproduce the magnitude of the daytime sensible heat fluxes
and especially the pronounced maximum observed in the afternoon. Additional model simulations indicate that this drawback
is to a large extent removed by the implementation of a shading factor in the original Deardorff scheme. The shading factor,
as discussed in Gryning et al. (2001), accounts for the fact that in areas with sparse vegetation and low solar angles, both
typical for the northern boreal forests in wintertime, absorption of direct solar radiation is due to an apparent vegetation
cover which is much greater than the actual one (defined as the portion of the ground covered by vegetation projected vertically).
Moreover, the observed asymmetry in the diurnal variation of the sensible heat flux indicates that there might be a significant
heat storage in the vegetation. The implementation of an objective heat storage scheme in the mesoscale model explains part
of the observed diurnal variation of the sensible heat flux.
Received November 12, 1999 Revised October 4, 2000 相似文献
9.
The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(T_(as)) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(T_s) over the TP. The cold biases are larger in T_(as) than in T_s, and are larger over the western TP. By decomposing the T_s bias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature bias.Strong negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models. 相似文献
10.
This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest version of the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Institute of Atmospheric Physics （IAP） （GAMIL1.1.0）. Considerable negative biases in all flux components, and thus an energy imbalance, are found in GAMIL1.1.0. In order to alleviate the energy imbalance, two modifications, namely an increase in cloud droplet effective radius and a decrease in cloud liquid water path, have been made to the cloud properties used in GAMIL. With the increased cloud droplet effective radius, the single scattering albedo of clouds is reduced, and thus the reflection of solar radiation into space by clouds is reduced and the net solar radiation flux at the top of the atmosphere is increased. With the reduced cloud optical depth, the net surface shortwave radiation flux is increased, causing a net warming over the land surface. This results in an increase in both sensible and latent heat fluxes over the land regions, which is largely balanced by the increased terrestrial radiation fluxes. Consequently, the energy balance at the top of atmosphere and at the surface is achieved with energy flux components consistent with available satellite observations. 相似文献
11.
南海夏季风爆发前后海-气界面热交换特征 总被引：20，自引：1，他引：20
文中利用 2 0 0 0与 2 0 0 2年二次南海海 气通量观测资料和同期西沙站资料 ,研究了南海夏季风爆发前后海洋表面热收支变化特征。研究表明 :南海夏季风爆发前后 ,影响海面热收支变化的主要分量是净短波辐射通量和潜热通量 ,在季风爆发前后不同阶段 ,二个分量的变化有不同表现形式 ,但不论二者如何变化 ,季风爆发与活跃期 ,海面热收入减小或为净支出 ;季风爆发前及中断期间 ,海面热收入逐渐增加 ;由于大的热惯性 ,海温变化落后于海面热收支的变化 ,海温的这种滞后效应通过影响潜热通量调节海面热收支的变化 ,又反过来影响自身的变化 ,形成短期振荡过程 ,这种振荡过程与季风的活跃、中断过程相对应。 相似文献
12.
中国西天山季节性积雪热力特征分析 总被引：3，自引：0，他引：3
利用中国天山积雪雪崩站干、湿雪雪层内每隔5min一次的10层雪温数据,探讨了一次降雪过程后干、湿雪的雪层温度特征,对比分析了干、湿雪的雪面能量平衡方程中各分量的差异。结果表明:(1)整个冬半年积雪各层温度基本<0℃,雪温日变化振幅由雪面向下逐渐减小,积雪深层温度的波峰(谷)值稍滞后于积雪浅层温度极值1～2天。(2)湿雪冷中心的出现时间早于干雪,暖中心的出现时间晚于干雪,太阳辐射对湿雪的穿透深度大于干雪。(3)雪层温度振幅变化与能量吸收随雪深都呈指数衰减分布。积雪密度越大,吸收系数越小,穿透深度越大。(4)干雪雪面的感热通量和潜热通量几乎都为负值,积雪积累。湿雪雪面的潜热通量与感热通量方向相反,互相抵消,所以净辐射是导致湿雪消融的主要因素。 相似文献
13.
利用2012年11月11日至2013年1月20日上海秋冬季涡动相关通量观测资料,对比分析地表能量平衡和CO2通量在不同天气条件下的日变化特征。结果表明：2012-2013年上海晴天和多云天气条件下,最大能量通量为储热项,其次为感热项;用于蒸发的潜热通量项最小,低于50 w·m-2。储热项日峰值出现在11时,出现时间早于净辐射通量,而在日落前转为负值。感热项日变化曲线并不以12时为中心呈对称分布,日落后感热项仍为明显正值。中午至日落时波文比值为3以上。感热通量受风向影响最大,在主导风向为西北风时,感热通量日峰值从其他风向的175 w·m-2左右减小至120 w·m-2左右。霾和云对短波辐射均表现为衰减作用,云的衰减作用明显大于霾。云使地表向上长波辐射和净长波辐射明显减少,而使大气逆辐射增加。晴天条件下,全天表现为CO2排放源,且日变化呈双峰型,两个峰值出现时间正好对应上下班高峰时段,傍晚峰值大于早上峰值。 相似文献
14.
The effect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo effect, which is compensated by weaker upward sensible heat flux associated with colder surface temperature, whereas the effects of snow melting and evaporation are relatively smaller.The anomalies of surface heat fluxes can last until June and become unobvions in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May.The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this influence is only obvious in early summer and almost disappears in later stages. 相似文献
15.
The multi-model ensemble (MME) of 20 models from the Coupled Model Intercomparison Project Phase Five (CMIP5) was used to analyze surface climate change in the 21st century under the representative concentration pathway RCP2.6, to reflect emission mitigation efforts. The maximum increase of surface air temperature (SAT) is 1.86°C relative to the pre-industrial level, achieving the target to limit the global warming to 2°C. Associated with the “increase-peak-decline” greenhouse gases (GHGs) concentration pathway of RCP2.6, the global mean SAT of MME shows opposite trends during two time periods: warming during 2006–55 and cooling during 2056–2100. Our results indicate that spatial distribution of the linear trend of SAT during the warming period exhibited asymmetrical features compared to that during the cooling period. The warming during 2006–55 is distributed globally, while the cooling during 2056–2100 mainly occurred in the NH, the South Indian Ocean, and the tropical South Atlantic Ocean. Different dominant roles of heat flux in the two time periods partly explain the asymmetry. During the warming period, the latent heat flux and shortwave radiation both play major roles in heating the surface air. During the cooling period, the increase of net longwave radiation partly explains the cooling in the tropics and subtropics, which is associated with the decrease of total cloud amount. The decrease of the shortwave radiation accounts for the prominent cooling in the high latitudes of the NH. The surface sensible heat flux, latent heat flux, and shortwave radiation collectively contribute to the especial warming phenomenon in the high-latitude of the SH during the cooling period. 相似文献
16.
利用区域气候模式Reg CM4.3(Regional Climate Mode version 4.3)对新疆地区冬季的地表状态进行了模拟分析,通过与ERA40再分析资料的对比分析发现,温度分布形势模拟较好,地面热力状态受地形影响显著,陡峭地形附近由于热性质差异大和非均匀性强会导致较大模拟误差;模式较好模拟出降水和潜热通量北疆多南疆少,山区多盆地少的分布特征,模拟出通过反照率影响,地表吸收的短波辐射呈现出沙漠腹地吸收多而天山地区吸收少的分布,对北疆呈感热通量汇而南疆呈感热通量源的感热分布形势也模拟较好;模拟的雪水当量与降水分布有较好的一致性,春季融雪径流与冬季雪水当量分布及降水均有较好的对应关系。通过模拟分析也发现,现有方案实际感热通量计算中以地面温度代替地面位温,造成感热通量偏小,因此会低估南疆感热源效应和高估北疆感热汇效应。此外,积雪量和地面温度模拟偏高可能是春季北疆主要积雪区径流偏强的原因。 相似文献
18.
19.
G J Boer 《Climate Dynamics》1993,8(5):225-239
The increase in the vigor of the hydrological cycle simulated in a 2 × CO2 experiment with the Canadian Climate Centre general circulation model is smaller than that obtained by other models which have similar increases in mean surface temperature. The surface energy budget, which encompasses also the moisture budget for the oceans, is analyzed. Changes in the net radiative input to and sensible heat flux from the surface act to warm it. This is balanced, at the new equilibrium, by a change in the latent heat flux which acts to cool it. Although this same general behavior is seen in other models, the increase in radiative input to the surface in the CCC GCM is smaller than in other models while the change in the sensible heat flux is of similar size. As a consequence, the latent heat flux required for balance is smaller. The comparatively small increase in the net radiative input at the surface occurs because of a decrease in the solar component. On average the decrease in solar input in the tropical region outweighs the higher latitude increase associated with the snow/ice albedo feedback. The notable tropical decrease in solar input occurs because the albedo of the clouds increase enough in this region to outweigh a small decrease in cloud amount. The increase in cloud albedo in the warmer and moister tropical atmosphere is a consequence of the parameterized cloud optical properties in the model which play an important role in the regulation of the surface energy and moisture budgets. The results demonstrate some of the consequences of the negative feedback mechanism associated with increasing cloud albedo in the model. They also suggest that the simulated change in the vigor of the hydrological cycle is not a simple function of the average increase in surface temperature but is a consequence of all of the processes in the model which control the available energy at the surface as a function of latitude. 相似文献
20.
The Grid-point Atmospheric Model of IAP LASG version 1.0 (GAMIL1.0) is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlance (1995)/Hack (1994) (ZM) and Tiedtke (1989)/Nordeng (1994) (TN).Two simulations are performed:one with the ZM scheme (EX_ZM) and the other with the TN scheme (EX_TN).The results indicate that during the convective process,more water vapor consumption and temperature increment are found in the EX_ZM,especially in the lower model layer,its environment is therefore very dry.In contrast,there is a moister atmosphere in the EX_TN,which favors low cloud formation and large-scale condensation,and hence more low cloud fraction,higher cloud water mixing ratio,and deeper cloud extinction optical depth are simulated,reflecting more solar radiative flux in the EX_TN.This explains why the TN scheme underestimates the net shortwave radiative flux at the top of the atmosphere and at surface.In addition,convection influences longwave radiation,surface sensible and latent heat fluxes through changes in cloud emissivity and precipitation. 相似文献