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1.
敦煌荒漠戈壁地区裸土地表反照率参数化研究 总被引：4，自引：1，他引：3
利用敦煌站观测资料,选取其中观测资料完整且连续性好的7个年份每年5～10月的地表净辐射四分量和土壤湿度资料,分析研究了敦煌荒漠戈壁地区裸土地表反照率与太阳高度角和表层土壤含水量之间的关系,结果表明:地表反照率与太阳高度角呈e指数关系,随太阳高度角的增大而减小,当太阳高度角大于40°时,地表反照率趋于稳定。表层土壤含水量的增大可导致地表反照率的减小,地表反照率与5 cm深土壤湿度呈线性关系。另外,建立了敦煌荒漠戈壁地区裸土地表反照率与太阳高度角和表层土壤含水量之间的双因子参数化公式,提出了一种更加适合该地区的地表反照率参数方案,并且选取2002年6～9月的实测资料对拟合的参数化公式进行模拟验证。本文所提出的地表反照率参数化方案能够很好地再现该地区裸土地表反照率的“U”型日变化特征,可准确地模拟出地表反照率的动态变化趋势。基于此参数化方案计算得到的地表反射辐射与实测值基本一致。 相似文献
2.
This heuristic study of the urban morphology influence on urban albedo is based on some 3,500 simulations with the Solene model. The studied configurations include square blocks in regular and staggered rows, rectangular blocks with different street widths, cross-shaped blocks, infinite street canyons and several actual districts in Marseilles, Toulouse and Nantes, France. The scanned variables are plan density, facade density, building height, layout orientation, latitude, date and time of the day. The sky-view factors of the ground and canopy surfaces are also considered. This study demonstrates the significance of the facade density, in addition to the built plan density, as the explanatory geometrical factor to characterize the urban morphology, rather than building height. On the basis of these albedo calculations the puzzling results of Kondo et al. (Boundary-Layer Meteorol 100:225–242, 2001) for the influence of building height are explained, and the plan density influence is quantitatively assessed. It is shown that the albedo relationship with plan and facade densities obtained with the regular square plot configuration may be considered as a reference for all other configurations, with the exception of the infinite street canyon that shows systematic differences for the lower plan densities. The curves representing this empirical relationship may be used as a sort of abacus for all other geometries while an approximate simple mathematical model is proposed, as well as relationships between the albedo and sky-view factors. 相似文献
3.
4.
To improve the simulation of the surface radiation budget and related thermal processes in arid regions, three sophisticated surface albedo schemes designed for such regions were incorporated into the Biosphere- Atmosphere Transfer Scheme （BATS）. Two of these schemes are functions of the solar zenith angle （SZA）, where the first one has one adjustable parameter defined as SZA1 scheme, and the second one has two empirical parameters defined as SZA2 scheme. The third albedo scheme is a function of solar angle and soil water that were developed based on arid-region observations from the Dunhuang field experiment （DHEX） （defined as DH scheme）. We evaluated the performance of the original and newly-incorporated albedo schemes within BATS using the in-situ data from the Oasis System Energy and Water Cycle Field Experiment that was carried out in JinTa, Gansu arid area （JTEX）. The results indicate that a control run by the original version of the BATS generates a constant albedo, while the SZA1 and SZA2 schemes basically can reproduce the observed diurnal cycle of surface albedo, although these two schemes still underestimate the albedo when SZA is high in the early morning and late afternoon, and overestimate it when SZA is low during noontime. The SZA2 scheme has a better overall performance than the SZA1 scheme. In addition, BATS with the DH scheme slightly improves the albedo simulation in magnitude as compared to that from the control run, but a diurnal cycle of albedo is not produced by this scheme. The SZA1 and SZA2 schemes significantly increase the surface absorbed solar radiation by nearly 70 W m^-2, which further raises the ground temperature by 6 K and the sensible heat flux by 35 W m^-2. The increased solar radiation, heat flux, and temperature are more consistent with the observations that those from the control run. However, a significant improvement in these three variables is not found in BATS with the DH scheme due to the neglect of the diurnal cycle of albedo. Further analysis indi 相似文献
5.
The surface albedo of two large cities in Japan was measured using a pyranometer mounted on a helicopter to avoid the bidirectional reflectance distribution. The daytime albedo was 0.12 in the cities, which was less than that of a nearby forest (0.16). The albedo was dependent on building structure in the cities; the albedo was lower in areas with more buildings, and decreased as the aspect ratio of street canyons increased. There are two reasons for this dependency: the multiple reflection of radiation in the building canopy, as has been shown in many previous studies, and the sparse vegetation in urban areas. These two factors concurrently determine the albedo in a real city, where the vegetation amount decreases as the plan roof ratio increases. 相似文献
6.
Snowfall and the subsequent evolution of the snowpack have a large effect on the surface energy balance and water cycle of the Tibetan Plateau (TP). The effects of snow cover can be represented by the WRF coupled with a land surface scheme. The widely used Noah scheme is computationally efficient, but its poor representation of albedo needs considerable improvement. In this study, an improved albedo scheme is developed using a satellite-retrieved albedo that takes snow depth and age into account. Numerical experiments were then conducted to simulate a severe snow event in March 2017. The performance of the coupled WRF/Noah model, which implemented the improved albedo scheme, is compared against the model’s performance using the default Noah albedo scheme and against the coupled WRF/CLM that applied CLM albedo scheme. When the improved albedo scheme is implemented, the albedo overestimation in the southeastern TP is reduced, reducing the RMSE of the air temperature by 0.7°C. The improved albedo scheme also attains the highest correlation between the satellite-derived and the model-estimated albedo, which provides for a realistic representation of both the snow water equivalent (SWE) spatial distribution in the heavy snowbelt (SWE > 6 mm) and the maximum SWE in the eastern TP. The underestimated albedo in the coupled WRF/CLM leads to underestimating the regional maximum SWE and a consequent failure to estimate SWE in the heavy snowbelt accurately. Our study demonstrates the feasibility of improving the Noah albedo scheme and provides a theoretical reference for researchers aiming to improve albedo schemes further. 相似文献
7.
M. P. Morassutti 《Theoretical and Applied Climatology》1991,44(1):25-36
Summary Three one-year experimental simulations with the National Center for Atmospheric Research Community Climate Model (NCAR CCM) were performed with three sea ice albedo parameterizations and compared with control run results to examine their impact on polar surface temperature, planetary albedo and clouds. The first integration utilized sea ice albedos of the Arctic Basin for the spring and summer of 1977 derived from defence Meteorological Satellite Imagery (DMSP). The second simulation employed prescribed lead and melt pond fractions and an albedo weighting scheme. The third simulation involved the coupling of an interactive sea ice/snow albedo parameterization made a function of surface state.Results show that prescribed, and assumed true satellite sea ice albedos produced higher planetary albedos than those calculated with the standard CCM sea ice albedo scheme in the control run. As a result, lower temperatures (up to 0.5 K) and increased cloudiness are generated for the Arctic region. The standard CCM sea ice albedo scheme is used as an adjustment to maintain normal temperatures for the polar oceans. The radiative impact of leads and melt ponds warmed sea ice regions only for short time periods. The third scheme generated markedly lower planetary albedos (reductions of 0.07 to 0.17) and higher surface temperatures (up to 2.0 K) than control values.The CCM simulates a gradual decrease in spring and summer Arctic cloud cover whereas observations show a sharp spring increase. Examination of the CCM code, particularly the cloud parameterization, is required to address this problem.With 12 Figures 相似文献
8.
Two competing cloud-radiative feedbacks identified in previous studies i.e., cloud albedo feedback and the super greenhouse effect, are examined in a sensitivity study with a global coupled ocean-atmosphere general circulation model. Cloud albedo feedback is strengthened in a sensitivity experiment by lowering the sea-surface temperature (SST) threshold in the specified cloud albedo feedback scheme. This simple parameterization requires coincident warm SSTs and deep convection for upper-level cloud albedos to increase. The enhanced cloud albedo feedback in the sensitivity experiment results in decreased maximum values of SST and cooler surface temperatures over most areas of the planet. There is also a cooling of the tropical troposphere with attendant global changes of atmospheric circulation reminiscent of those observed during La Niña or cold events in the Southern Oscillation. The strengthening of the cloud albedo feedback only occurs over warm tropical oceans (e.g., the western Pacific warm pool), where there is increased albedo, decreased absorbed solar radiation at the surface, stronger surface westerlies, enhanced westward currents, lower temperatures, and decreased precipitation and evaporation. However, the weakened convection over the tropical western Pacific Ocean alters the large-scale circulation in the tropics such that there is increased upper-level divergence over tropical land areas and the tropical Indian Ocean. This results in increased precipitation in those regions and intensified monsoonal regimes. The enhanced precipitation over tropical land areas produces increased clouds and albedo and wetter and cooler land surfaces. These additional contributions to decreased absorbed solar input at the surface combine with similar changes over the tropical oceans to produce the global cooling associated with the stronger cloud albedo feedback. Increased low-level moisture convergence and precipitation over the tropical Indian Ocean enhance slightly the super greenhouse effect there. But the stronger cloud albedo feedback is still the dominant effect, although cooling of SSTs in that region is less than in the tropical western Pacific Ocean. The sensitivity experiment demonstrates how a regional change of radiative forcing is quickly transmitted globally through a combination of radiative and dynamical processes in the coupled model. This study points to the uncertainties involved with the parameterization of cloud albedo and the major implications of such parameterizations concerning the maximum values of SST, global climate sensitivity, and climate change.Support is provided by the Office of Health and Environmental Research of the U.S. Department of Energy, as part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
9.
A new canopy radiation transfer and surface albedo scheme is developed as part of the land surface model EALCO (Ecological
Assimilation of Land and Climate Observations). The model uses a gap probability-based successive orders of scattering approach
that explicitly includes the heterogeneities of stands and crown elements and the radiation multiple scattering. The model
uses the optical parameters of ecosystem elements and physically represents ecosystem processes in surface albedo dynamics.
Model tests using measurements from a boreal deciduous forest ecosystem show that the model well reproduced the observed diurnal
and seasonal albedo dynamics under different weather and ecosystem conditions. The annual mean absolute errors between modeled
and measured daily albedo and reflected radiation are 0.01 and 1.33 W m−2, respectively. The model results provide a quantitative assessment of the impacts of plant shading and sky conditions on
surface albedo observed in high-latitude ecosystems. The contribution of ground snow to surface albedo in winter was found
to be less than 0.1 even though the canopy is leafless during this time. The interception of snow by the leafless canopy can
increase the surface albedo by 0.1–0.15. The model results show that the spectral properties of albedo have large seasonal
variations. In summer, the near infrared component is substantially larger than visible, and surface albedo is less sensitive
to sky conditions. In winter, the visible band component is markedly increased and can exceed the near infrared proportion
under cloudy conditions or when snow exists on the canopy. The spectral properties of albedo are also found to have large
diurnal variations under the clear-sky conditions in winter. 相似文献
10.
K. Fortuniak 《Theoretical and Applied Climatology》2008,91(1-4):245-258
Summary The paper focuses on the absorption of shortwave radiation in an urban street canyon. To test the effective albedo of the
canyon an analytic solution of the multiple reflection problem is applied. The infinitesimally long canyon is divided into
slices and a matrix of view factors for the slices is defined. Incoming shortwave radiation includes direct and diffuse parts
and shadowing effects are included in the analysis. The model is validated against Aida’s (1982) scale model data and measurements
in a real canyon. The results demonstrate a rapid decrease of the effective albedo as the canyon aspect ratio (its height
to width, H/W) are increased. It is also shown that diurnal changes of the effective albedo can be very complex depending on the particular
combination of H/W ratio, surface reflectivity and canyon orientation.
Author’s address: Krzysztof Fortuniak, Department of Meteorology and Climatology, University of Łódź, Narutowicza 88, 09-139
Łódź, Poland. 相似文献
11.
比较Morcrette辐射方案和Fu_Liou辐射方案对NCC/IAP T63海气耦合模式云和辐射模拟的影响, 结果表明:两种方案模拟的大气顶入射辐射存在明显的差异; 晴空大气Fu_Liou方案的短波吸收能力在全球普遍较Morcrette方案低; 在60°S~60°N之间, Fu_Liou方案模拟的行星反照率更接近于ERBE卫星观测; 在对大气顶净辐射的模拟上, 除了冬季的太平洋和大西洋东岸云量明显减少的部分地区外, Fu_Liou方案对大气顶净辐射的模拟总体上较Morcrette方案有了较为明显的改善; Fu_Liou方案模拟的海洋低层云显著减少, 而热带地区高云的模拟明显增加; 由于采用了“二元云量”算法, 尽管云量有所减少, Fu_Liou方案模拟的云短波吸收作用仍有所增强, 一定程度上改进了Morcrette方案云的短波吸收作用偏弱的现象。 相似文献
12.
Potential impact of albedo incorporation in boreal forest sector climate change policy effectiveness
Forests have an important role to play in climate change mitigation through carbon sequestration and wood supply. However, the lower albedo of mature forests compared to bare land implies that focusing only on GHG accounting may lead to biased estimates of forestry's total climatic impacts. An economic model with a high degree of detail of the Norwegian forestry and forest industries is used to simulate GHG fluxes and albedo impacts for the next decades. Albedo is incorporated in a carbon tax/subsidy scheme in the Norwegian forest sector using a partial, spatial equilibrium model. While a price of EU€100/tCO2e that targets GHG fluxes only results in reduced harvests, the same price including albedo leads to harvest levels that are five times higher in the first five years, with 39% of the national productive forest land base being cleared. The results suggest that policies that only consider GHG fluxes and ignore changes in albedo will not lead to an optimal use of the forest sector for climate change mitigation.Policy relevanceBare land reflects a larger share of incoming solar energy than dense forest and thus has higher albedo. Earlier research has suggested that changes in albedo caused by management of boreal forest may be as important as carbon fluxes for the forest's overall global warming impacts. The presented analysis is the first attempt to link albedo to national-scale forest climate policies. A policy with subsidies to forest owners that generate carbon sequestration and taxes levied on carbon emissions leads to a reduced forest harvest. However, including albedo in the policy alongside carbon fluxes yields very different results, causing initial harvest levels to increase substantially. The inclusion of albedo impacts will make harvests more beneficial for climate change mitigation as compared to a carbon-only policy. Hence, it is likely that carbon policies that ignore albedo will not lead to optimal forest management for climate change mitigation. 相似文献
13.
Calculation of solar albedo and radiation equilibrium over the Qinghai-Xizang Plateau and analysis of their climatic features 总被引：1，自引：0，他引：1
1.IntroductionTopreciselyestimatethevaluesofalbedosatsurfaceandatmospherictop.surfacetotalradiationandearth--atmosphereoutgoinglongwaveradiationiscrucialtocalculatingradiationbalanceatsurfaceandatmospherictopandexploringoftheeffectoftheQXPatmosphericheatsourcesonatmosphericcirculations.Using1958--1960observationsofsurfacetotalradiation,albedoandsurfacemeteorologicalobservationsoverChina.ChenandGongetal.(1964.1965)investigated,throughanatmosphericradiationcalculationscheme.thedistributionchar… 相似文献
14.
Parameterization of snow-free land surface albedo as a function of vegetation phenology based on MODIS data and applied in climate modelling 总被引：1，自引：0，他引：1
Diana Rechid Thomas J. Raddatz Daniela Jacob 《Theoretical and Applied Climatology》2009,95(3-4):245-255
The aim of this study was to develop an advanced parameterization of the snow-free land surface albedo for climate modelling describing the temporal variation of surface albedo as a function of vegetation phenology on a monthly time scale. To estimate the effect of vegetation phenology on snow-free land surface albedo, remotely sensed data products from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on board the NASA Terra platform measured during 2001 to 2004 are used. The snow-free surface albedo variability is determined by the optical contrast between the vegetation canopy and the underlying soil surface. The MODIS products of the white-sky albedo for total shortwave broad bands and the fraction of absorbed photosynthetically active radiation (FPAR) are analysed to separate the vegetation canopy albedo from the underlying soil albedo. Global maps of pure soil albedo and pure vegetation albedo are derived on a 0.5° regular latitude/longitude grid, re-sampling the high-resolution information from remote sensing-measured pixel level to the model grid scale and filling up gaps from the satellite data. These global maps show that in the northern and mid-latitudes soils are mostly darker than vegetation, whereas in the lower latitudes, especially in semi-deserts, soil albedo is mostly higher than vegetation albedo. The separated soil and vegetation albedo can be applied to compute the annual surface albedo cycle from monthly varying leaf area index. This parameterization is especially designed for the land surface scheme of the regional climate model REMO and the global climate model ECHAM5, but can easily be integrated into the land surface schemes of other regional and global climate models. 相似文献
15.
Xiwei Yin 《Theoretical and Applied Climatology》1998,60(1-4):121-140
Summary The albedo of vegetated land surfaces (surface albedo) is a key factor in climate modeling and in mechanistic accounting
of many ecological processes. This paper proposes a testable numerical equation for the analysis and projection of surface
albedo. Conceptualized as the manifestation of a canopy elements-determined basic property after modifications by temporal
and spatial circumstances, surface albedo was depicted analytically in relation to 11 driving variables (leaf size, leaf life
span, relative leaf age, canopy leaf cover, relative stem cover, vegetation height, stress-calendar day, drought indicator,
optical air mass, station atmospheric pressure, snow cover). With peripheral algorithms developed to derive all but two of
those variables, surface albedo was linked ultimately to eight rudimentary factors (calendar day, latitude, elevation, vegetation
height, dominant plant species, monthly air temperature, monthly precipitation, snow cover).
The analytical framework, and then its coefficient values, for surface albedo were generally supported by a series of statistical
evaluations in terms of: (i) the equation’s ability to capture, by regression fitting, the variation in the surface albedo of 26 forests (135 data points)
distributed around the world; (ii) the quantitative significance of individual driving variables; (iii) the randomness of residual or error distributions; (iv) the performance of the forests-fitted equation in extrapolative prediction of surface albedo against independent data for
8 deforested sites (93 data points) and for 3 types of vegetation (7 data points) at the Arctic treeline. Compared to the
data, the fitted or projected albedo values had a margin of error generally within ±10%. The individual coefficient values
and component functions of the final equation were consistent with their supposed mechanistic underpinnings, based on independent
information from the literature. The equation shed new insight into the quantitative behavior of surface albedo, and upon
further validation, should be useful for modeling surface albedo as a key land surface-atmosphere feedback link that varies
and interacts with climate and vegetation.
Received August 18, 1997 相似文献
16.
一种单层城市冠层模式的建立及数值试验研究 总被引：3，自引：1，他引：2
本文在引进先进的城市地表能量平衡方案 (Town Energy Balance, 简称TEB) 的基础上建立了一个单层城市冠层模式, 并对南京市典型居民区1 km2范围内的局地尺度地表能量平衡各分量进行离线模拟, 将模拟结果与同期观测值作了比对, 发现: TEB方案对城市地表能量平衡各分量的模拟效果良好, 而该方案的模拟性能受建筑物表面材料反照率取值的影响较大。在离线研究的基础上, 本文又将TEB方案成功耦合到南京大学区域边界层模式 (NJU－RBLM) 中, 作为该模式的地表能量平衡参数化方案之一, 分别选取该边界层模式中原有的地表能量平衡参数化方案SVAT (Soil－Vegetation－Atmosphere－Transfer model) 和新引入的TEB方案对冬夏两季不同个例进行模拟, 以常规近地面气温观测资料和Landsat卫星观测的地表反照率资料对模拟结果进行比较, 结果表明: TEB方案对原大气边界层模式的模拟效果有明显改善, 对近地面热力场的改善效果尤为明显, 可以很好地模拟出城市冠层中的“陷阱效应”。 相似文献
17.
Summary Sky luminance and spectral radiance has been characterised at Neumayer, Antarctica for selected situations during the austral
summer 2003/04. Luminance has also been measured at Boulder, Colorado, USA in June 2003. The high reflectivity of the surface
(albedo) in Antarctica, reaching values up to 100% in the ultraviolet (UV) and visible part of the solar spectrum due to snow
cover, modifies the radiation field considerably when compared to mid-latitudes. A dependence of luminance and spectral radiance
on solar zenith angle (SZA) and surface albedo has been identified. For snow and cloudless sky, the horizon luminance exceeds
the zenith luminance by as much as a factor of 8.2 and 7.6 for a SZA of 86° and 48°, respectively. In contrast, over grass
this factor amounts to 4.9 for a SZA of 86° and a factor of only 1.4 for a SZA of 48°. Thus, a snow surface with high albedo
can enhance horizon brightening compared to grass by a factor of 1.7 for low sun at a SZA of 86° and by a factor of 5 for
high sun at a SZA of 48°. For cloudy cases, zenith luminance and radiance exceed the cloudless value by a factor of 10 due
to multiple scattering between the cloud base and high albedo surface. Measurements of spectral radiance show increased horizon
brightening for increasing wavelengths and generally confirm the findings for luminance. Good agreement with model results
is found for some cases; however there are also large deviations between measured and modelled values especially in the infrared.
These deviations can only partly be explained by measurement uncertainties; to completely resolve the differences between
model and measurement further studies need to be performed, which will require an improvement of modelling the spectral radiance.
From the present study it can be concluded that a change in albedo conditions, which is predicted as a consequence of climate
change, will significantly change the radiation conditions in polar regions as well. 相似文献
18.
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
19.
20.
Sebastian Schubert Susanne Grossman-Clarke Alberto Martilli 《Boundary-Layer Meteorology》2012,145(3):439-468
We develop a double-canyon radiation scheme (DCEP) for urban canopy models embedded in mesoscale numerical models based on the Building Effect Parametrization (BEP). The new scheme calculates the incoming and outgoing longwave and shortwave radiation for roof, wall and ground surfaces for an urban street canyon characterized by its street and building width, canyon length, and the building height distribution. The scheme introduces the radiative interaction of two neighbouring urban canyons allowing the full inclusion of roofs into the radiation exchange both inside the canyon and with the sky. In contrast to BEP, we also treat direct and diffuse shortwave radiation from the sky independently, thus allowing calculation of the effective parameters representing the urban diffuse and direct shortwave radiation budget inside the mesoscale model. Furthermore, we close the energy balance of incoming longwave and diffuse shortwave radiation from the sky, so that the new scheme is physically more consistent than the BEP scheme. Sensitivity tests show that these modifications are important for urban regions with a large variety of building heights. The evaluation against data from the Basel Urban Boundary Layer Experiment indicates a good performance of the DCEP when coupled with the regional weather and climate model COSMO-CLM. 相似文献