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1.
地面热红外发射率的天顶角变化效应 总被引：1，自引：0，他引：1
文中着重研究了自然地表面的红外辐射的方向特征 ,实地测量了发射率随观测天顶角的变化 ,分别对卫星资料反演地面温度和地面辐射测量作出红外发射率的观测天顶角修正 ,两者比较的结果表明 ,发射观测天顶角修正在精确地面温度的反演计算中不可忽视 ,尤其在大角度观测情况下 ,对某些地物发射率方向特征的修正比发射率本身的修正更重要。 相似文献
2.
Summary The dependence of the albedo on illumination direction is analyzed by constructing a canopy model in which the individual leaves are planar, Lambertian reflectors. Leaf transmission is treated separately, and is assumed to be proportional to the cosine of the zenith angle of the leaf normal. Effects of shading and obscuration are formulated assuming random distribution of the leaves with respect to the viewing and illumination directions. Variants of the model with different azimuthal leaf distributions are created and discussed as explicit expressions of the viewing/illumination geometry and the canopy characteristics.The canopy spectral single-scattering albedo factors, which are the conditional probabilities of a photon escaping from the canopy after a first reflection or a first transmission, are obtained by numerical integration over a hemisphere of the bidirectional reflectance and transmittance factors. Our analysis identifies the ratio of the projection of leaf area on the vertical plane perpendicular to the principal plane to that on a horizontal plane as the parameter that controls the dependence of the albedo on the solar zenith angle. The albedo factor due to the leaf transmittance generally increases with the zenith angle of illuminating beam more sharply than that due to the leaf reflectance.Model variants with various azimuthal distributions are compared with measured albedo of soybeans. Second and higher order scatterings are accounted for in a simplified way. The degree to which a model variant fits the measured albedo and its change with the solar zenith angle depends both on the leaf inclination angleand the azimuthal distribution of the leaf area.With 6 Figures 相似文献
3.
R. L. Raddatz T. Papakyriakou R. J. Galley M. G. Asplin L. M. Candlish B. Else 《大气与海洋》2013,51(5):489-504
The 2009 ArcticNet expedition was a field campaign in the Amundsen Gulf–eastern Beaufort Sea region from mid-July to the beginning of November aboard the CCGS Amundsen that provided an opportunity to describe the all-sky surface radiation and the clear-sky surface energy budgets from summer to freeze-up in the data sparse western maritime Arctic. Because the fractional area of open water was generally larger than the fractional area of ice floes, the net radiation at the water surface controlled the radiation budget. Because the water albedo is much less than the albedo of the ice floes, the extent and duration of open water in summer is an important albedo feedback mechanism. From summer to freeze-up, the net all-sky shortwave radiation declined steadily as the solar angle lowered, while coincidently the net all-sky longwave radiation became increasingly negative. The all-sky net surface radiation switched from positive in summer to negative during the freeze-up period. From summer to freeze-up, both upward and downward turbulent heat fluxes occurred. In summer, a positive surface energy budget residual contributed to the melting of ice floes and/or to the warming of the Arctic Ocean's mixed layer. During the freeze-up period, with temperatures below approximately ?5°C, the residuals were mainly negative suggesting that heat loss from the ocean's mixed layer and heat released by the phase change of water were significant components of the energy budget's residual. 相似文献
4.
Recent changes in the Arctic hydrological cycle are explored using in situ observations and an improved atmospheric reanalysis data set, ERA-Interim. We document a pronounced decline in summer snowfall over the Arctic Ocean and Canadian Archipelago. The snowfall decline is diagnosed as being almost entirely caused by changes in precipitation form (snow turning to rain) with very little influence of decreases in total precipitation. The proportion of precipitation falling as snow has decreased as a result of lower-atmospheric warming. Statistically, over 99% of the summer snowfall decline is linked to Arctic warming over the past two decades. Based on the reanalysis snowfall data over the ice-covered Arctic Ocean, we derive an estimate for the amount of snow-covered ice. It is estimated that the area of snow-covered ice, and the proportion of sea ice covered by snow, have decreased significantly. We perform a series of sensitivity experiments in which inter-annual changes in snow-covered ice are either unaccounted for, or are parameterized. In the parameterized case, the loss of snow-on-ice results in a substantial decrease in the surface albedo over the Arctic Ocean, that is of comparable magnitude to the decrease in albedo due to the decline in sea ice cover. Accordingly, the solar input to the Arctic Ocean is increased, causing additional surface ice melt. We conclude that the decline in summer snowfall has likely contributed to the thinning of sea ice over recent decades. The results presented provide support for the existence of a positive feedback in association with warming-induced reductions in summer snowfall. 相似文献
5.
M. Nunez 《Boundary-Layer Meteorology》1985,33(4):379-395
A simple model is developed which estimates daily global radiation at the floor of a non-homogeneous Eucalyptus forest. Model input parameters are easily derived from field measurements and consist of individual tree location, tree height, maximum canopy width and its corresponding height, height of the lowest branch and trunk thickness. In addition, the model requires values for global and diffuse irradiance in the open. The tree canopy is represented as a series of spheres containing leaves which are homogeneously spaced but are oriented in the vertical plane. This configuration closely approaches that of actual eucalyptus trees. A Monte-Carlo approach is used to estimate the albedo of the unit sphere as a function of solar zenith angle. At a given combination of solar zenith and azimuth angle, the model estimates the solar irradiance at a specific forest floor location.The model, when tested against pyranometer measurements, predicted daily solar irradiance with a correlation of 0.98 and a standard error of 0.98 MJ m-2 day-1. This good performance is attributed to the spatial averaging of the radiation fluxes over the entire day, and the relatively low sensitivity of the calculated solar irradiance to sphere albedo. 相似文献
6.
All-weather Arctic cloud analyses primarily derived from a surface-based hemispheric all-sky imager are compared against ISCCP D-1 cloud amount, type, and phase during the sunlit polar season. Increasing surface temperatures and decreasing ice cover over the past decade have altered heat and moisture fluxes around the Arctic, providing conditions more conducive for cloud generation. Shipboard and ice camp measurements from field experiments conducted over an 8-year period show cloudy skies in 70–95% of the record. Most of these occurrences are stratiform or multi-level, multi-form cloud, increasing in amount with time through the season. Collocated ISCCP retrievals underestimate cloud amount at small solar zenith angles and overestimate at large angles, sometimes by as much as 50%. Satellite assessments of cloud form classify 95% of scenes as having multiple cloud types, the majority of which are mid-level ice cloud and low-level liquid cloud. Despite large discrepancies in diurnal cloud amount, regional averages of ISCCP pixel cloudiness over the length of the experiments agree within ±5% of surface observations. 相似文献
7.
国家气候中心气候系统模式BCC_CSM2.0最新耦合了美国Los Alamos国家实验室发展的海冰模式CICE5.0,为试验模式中与反照率相关参数的敏感性及其对模拟结果的影响,提高模式对北极海冰的模拟能力,选取海冰模式中3个主要参数进行了敏感性试验。利用以BCC_CSM2.0耦合框架为基础建立的海冰-海洋耦合模式,选取CORE资料为大气强迫场开展试验,试验的3个参数分别为冰/雪表面反射率、雪粒半径和雪粒半径参考温度。结果表明,参数取值的不同对北极海冰的模拟有显著的影响,优化后的取值组合极大提高了模式的模拟能力,主要表现在:（1）改善了对北极冬季海冰厚度的模拟,海冰厚度增大,与观测资料更为吻合;（2）显著提高了对北极夏季海冰密集度的模拟能力,从而模拟的北极海冰范围年际循环与观测更为一致。参数取值的优化改进了模式对海冰反照率的模拟,进而影响了冰面短波辐射的吸收和海冰表层的融化,最终提高了模式对海冰密集度和厚度的模拟效果。 相似文献
8.
Measurements of incoming global, diffuse and reflected radiation at a tower site in Lake Ontario are used to evaluate components of surface albedo. Albedo for diffuse radiation lies between 0.074 and 0.082 and a coefficient for backscatter from sub-surface water layers shows little deviation from a mean of 0.017. Direct beam albedo for a calm surface follows the Fresnel law. Waves increase direct-beam albedo particularly at higher solar zenith angles. A pronounced dependence of albedo upon zenith angle for clear skies decreases with increasing cloud amount and becomes undetectable in overcast conditions. On a daily basis, albedo ranged between 0.07 in early July to 0.11 in mid-November. Day-to-day scatter is within ±1% of the mean seasonal trend. 相似文献
9.
Desert targets for solar channel calibration of geostationary satellites in the East Asia — Australian region were selected and their qualities were assessed with aid of Moderate Resolution Imaging Spectroradiometer data (i.e., white-sky surface albedo, aerosol optical thickness, and cloud fraction) from 2002 to 2008. The magnitude, spatial uniformity, and temporal stability of the white-sky surface albedo are examined in order to select bright and stable targets. Subsequently those selected targets over China, India, and Australia are further checked for their qualities in terms of data yielding ratio, aerosol optical thickness, cloud fraction, satellite viewing angle, and solar zenith angle. Results indicate that Chinese targets are found to be not adequate as calibration targets in spite of excellent surface conditions because of high percentage of cloud, possibly heavy aerosol loading, and lower solar elevation angle in particular during winter time. Indian site should be take care about relatively high temporal variation of surface condition and heavy aerosol loading. On the other hand, Australian desert targets are considered to be best when surface brightness, spatial and temporal stability, data yielding ratio, aerosol, and cloud are counted. 相似文献
10.
Urban albedo as a function of the urban structure — A two-dimensional numerical simulation 总被引：4，自引：0，他引：4
Urban albedo change as a function of urban geometrical structure has been examined by using a two-dimensional urban block-canyon array model. The complex multiple reflections of incident photons in the urban canyon are simulated by using a Monte-Carlo method. The photons are tracked until they leave the canyon or are completely absorbed. In the model, the direct and diffuse components of incident solar radiation are introduced and the specular and isotropic reflection characteristics are considered for the relevant urban surfaces. The result shows that the urban albedo decreases as the urban irregularity increases as indicated by the model experiment of Aida (1982). The dependence of albedo on the incident solar zenith angle observed in the experiment is also confirmed for various urban models.As an application, some actual urban structures in the Marunouchi area in Tokyo are examined. Urban planning for absorption and reflection of solar radiation in urban areas is also discussed based on the analysis of the change in albedo with canyon dimensions and solar zenith angle. 相似文献
11.
Radiative transfer model simulations were used to investigate the erythemal ultraviolet(EUV) correction factors by separating the UV-A and UV-B spectral ranges. The correction factor was defined as the ratio of EUV caused by changing the amounts and characteristics of the extinction and scattering materials. The EUV correction factors(CFEUV) for UV-A[CFEUV(A)] and UV-B [CFEUV(B)] were affected by changes in the total ozone, optical depths of aerosol and cloud, and the solar zenith angle. The differences between CFEUV(A) and CFEUV(B) were also estimated as a function of solar zenith angle, the optical depths of aerosol and cloud, and total ozone. The differences between CFEUV(A) and CFEUV(B) ranged from-5.0% to 25.0% for aerosols, and from-9.5% to 2.0% for clouds in all simulations for different solar zenith angles and optical depths of aerosol and cloud. The rate of decline of CFEUV per unit optical depth between UV-A and UV-B differed by up to 20% for the same aerosol and cloud conditions. For total ozone, the variation in CFEUV(A) was negligible compared with that in CFEUV(B) because of the effective spectral range of the ozone absorption band. In addition, the sensitivity of the CFEUVs due to changes in surface conditions(i.e., surface albedo and surface altitude) was also estimated by using the model in this study. For changes in surface albedo, the sensitivity of the CFEUVs was 2.9%–4.1% per 0.1 albedo change,depending on the amount of aerosols or clouds. For changes in surface altitude, the sensitivity of CFEUV(B) was twice that of CFEUV(A), because the Rayleigh optical depth increased significantly at shorter wavelengths. 相似文献
12.
Summary The diffuse sky radiation component in the ultraviolet wavelengths is often at least 50% of the global irradiance under clear skies, and is the dominant component of ultraviolet global radiation under translucent overcast skies. The distribution of sky radiance was measured in a rural area and modeled for wavelength bands of ultraviolet-B (UVB, 280–320 nm) and ultraviolet-A (UVA, 320–400 nm). Sky radiance measurements were made during the summer of 1993 over a wide range of solar zenith angles using radiance sensors mounted on a hand-operated hemispherical rotation mount. UVB irradiance measurements were also made during each scan. Since the ratio of measured irradiance under overcast skies and that predicted for clear skies was not correlated with cloud base height, opaque cloud fraction, or solar zenith angle, it was concluded that the scattering from the clouds dominated the global irradiance, and this scattering was relatively unaffected by the scattering off opaque clouds in the translucent atmosphere.Analysis of the translucent overcast sky UVA and UVB radiance measurements using a semi-empirical distribution model showed that the spectral influences on multiple scattering, single scattering, and horizon brightening components of the distributions agreed with basic atmospheric radiation theory. The best model used solar zenith, the sky zenith, and the scattering angle with resultant coefficient of determination values of 0.62 and 0.25 for the UVA and UVB respectively. The developed equations can be applied directly to the diffuse sky irradiance on the horizontal to provide radiance distributions for the sky.With 6 Figures 相似文献
13.
The effects of sea surface temperature (SST), radiation, cloud microphysics, and diurnal variations on the vertical structure of tropical tropospheric temperature are investigated by analyzing 10 two-dimensional equilibrium cloud-resolving model simulation data. The increase of SST, exclusion of diurnal variation of SST, and inclusion of diurnal variation of solar zenith angle, radiative effects of ice clouds, and ice microphysics could lead to tropical tropospheric warming and increase of tropopause height. The increase of SST and the suppression of its diurnal variation enhance the warming in the lower and upper troposphere, respectively, through increasing latent heat and decreasing IR cooling. The inclusion of diurnal variation of solar zenith angle increases the tropospheric warming through increasing solar heating. The inclusion of cloud radiative effects increases tropospheric warming through suppressing IR cooling in the mid and lower troposphere and enhancing solar heating in the upper troposphere. The inclusion of ice microphysics barely increases warming in the mid and lower troposphere because the warming from ice radiative effects is nearly offset by the cooling from ice microphysical effects, whereas it causes the large warming enhancement in the upper troposphere due to the dominance of ice radiative effects. The tropopause height is increased mainly through the large enhancement of IR cooling. 相似文献
14.
用于空间对地遥感的一个参数化辐射传输计算模式 总被引：4，自引：1，他引：3
一个足够精度的参数化向上亮度模式对空间对地遥感的大气订正应用是很有意义的。依据向上天空亮度对大气散射相函数、光学厚度、太阳天顶角、空间方位和天顶角等有关参数的依赖特性,基于大量的天空亮度数值模拟计算资料,本文发展了一个关于向上天空亮度的参数化模式。39440组的数值模拟对比资料表明,在气溶胶光学厚度#Aτt≤1,太阳天顶角小于72°,μ≤0.432 （天顶角小于65°）以及无云的条件下,由现在的参数化的模式所计算的向上亮度的误差一般小于6%。地表反射率越大,参数化模式的精度越高。参数化模式的精度一般随着光学厚度和太阳天顶角的增大而变差。 相似文献
15.
Submarine and satellite observations show that the Arctic Ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades. Here the response of the Arctic Ocean ice cover to changes in the poleward atmospheric energy transport, F wall, is investigated using coupled atmosphere-ice-ocean column models. Two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness—ice volume export feedback and the positive surface albedo feedback. The steady state ice thickness as a function of F wall is determined for various model setups and defines what we call ice thickness response curves. When a variable surface albedo and snow precipitation is included, a complex response curve appears with two distinct regimes: a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime. The two regimes are separated by a steep transition associated with surface albedo feedback. The associated hysteresis is however small, indicating that the Arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback. The results are discussed in the context of the recent reduction of the Arctic sea ice cover. A new mechanism related to regional and temporal variations of the ice divergence within the Arctic Ocean is presented as an explanation for the observed regional variation of the ice thickness reduction. Our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i.e. large areas of the Arctic Ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness, corresponding to the above mentioned transition, and into a state dominated by seasonal ice. 相似文献
16.
The influence of various cloud parameters and the interactions with the ground albedo and the solar zenith angle have been studied by means of model simulations. The radiative transfer model suitable for a cloudy atmosphere as well as for a clear atmosphere has been developed on the basis of the Discrete Ordinate Method. This study leads to a general understanding for cloudy atmospheres: in the presence of a uniform cloud, the cloud scattering is dominant to molecular and aerosol scattering, and it is also wavelength-independent; the ratio of transmitted irradiance in a cloudy atmosphere to that in the background clear atmosphere is independent of cloud height and solar zenith angle. That’s to say, the radiation downwelling out of a cloud is quite isotropic; it decreases approximately exponentially with the cloud optical depth at a rate related to the ground albedo; the reflected irradiance at the top of the atmosphere is dependent on cloud optical depth as well as on solar zenith angle, but not on ground albedo for clouds of not very thin optical depth. 相似文献
17.
Sea ice formed over shallow Arctic shelves often entrains sediments resuspended from the sea floor. Some of this sediment-laden ice advects offshore into the Transpolar Drift Stream and the Beaufort Gyre of the Arctic Basin. Through the processes of seasonal melting at the top surface, and the freezing of clean ice on the bottom surface, these sediments tend, over time, to concentrate at the top of the ice where they can affect the surface albedo, and thus the absorbed solar radiation, when the ice is snow free. Similarly, wind-blown dust can reduce the albedo of snow. The question that is posed by this study is what is the impact of these sediments on the seasonal variation of sea ice, and how does it then affect climate? Experiments were conducted with a coupled energy balance climate-thermodynamic sea ice model to examine the impact of including sediments in the sea ice alone and in the sea ice and overlying snow. The focus of these experiments was the impact of the radiative and not the thermal properties of the sediments. The results suggest that if sea ice contains a significant amount of sediments which are covered by clean snow, there is only a small impact on the climate system. However, if the snow also contains significant sediments the impact on sea ice thickness and surface air temperature is much more significant. 相似文献
18.
Joseph Sedlar Michael Tjernström Thorsten Mauritsen Matthew D. Shupe Ian M. Brooks P. Ola G. Persson Cathryn E. Birch Caroline Leck Anders Sirevaag Marcel Nicolaus 《Climate Dynamics》2011,37(7-8):1643-1660
Snow surface and sea-ice energy budgets were measured near 87.5°N during the Arctic Summer Cloud Ocean Study (ASCOS), from August to early September 2008. Surface temperature indicated four distinct temperature regimes, characterized by varying cloud, thermodynamic and solar properties. An initial warm, melt-season regime was interrupted by a 3-day cold regime where temperatures dropped from near zero to ?7°C. Subsequently mean energy budget residuals remained small and near zero for 1 week until once again temperatures dropped rapidly and the energy budget residuals became negative. Energy budget transitions were dominated by the net radiative fluxes, largely controlled by the cloudiness. Variable heat, moisture and cloud distributions were associated with changing air-masses. Surface cloud radiative forcing, the net radiative effect of clouds on the surface relative to clear skies, is estimated. Shortwave cloud forcing ranged between ?50 W m?2 and zero and varied significantly with surface albedo, solar zenith angle and cloud liquid water. Longwave cloud forcing was larger and generally ranged between 65 and 85 W m?2, except when the cloud fraction was tenuous or contained little liquid water; thus the net effect of the clouds was to warm the surface. Both cold periods occurred under tenuous, or altogether absent, low-level clouds containing little liquid water, effectively reducing the cloud greenhouse effect. Freeze-up progression was enhanced by a combination of increasing solar zenith angles and surface albedo, while inhibited by a large, positive surface cloud forcing until a new air-mass with considerably less cloudiness advected over the experiment area. 相似文献
19.
It is demonstrated within the frameworks of the analysis of determination methods of snowice cover reflectance that the problem
of the measurement technique of hummocky formation albedo has not been studied enough. The results of in situ experiments
carried out on the Arctic sea ice are presented. The results of ice hummock albedo measurements using different techniques
are discussed. The need to organize the special experimental research for the development of practical recommendations for
estimating the hummocky formation albedo is declared. 相似文献
20.
Abstract A three‐component (isotropic, circumsolar and horizon‐brightening) model of the angular distribution of sky (short‐wave) radiance has been tested and validated against a data base of measured sky radiance. The data base encompasses cloud cover 0.0 to 1.0 and solar zenith angles 30 to 80°. Empirical constants have been derived for the model enabling the prediction of sky radiances for any sky condition. 相似文献