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1.
A novel approach for upscaling land-surface parameters based on inverse stochastic surface-vegetation-atmosphere transfer
(SVAT) modelling is presented. It allows estimation of effective parameters that yield scale invariant outputs e.g. for sensible
and latent heat fluxes and evaporative fraction. The general methodology is used to estimate effective parameters for the
Oregon State University Land-Surface Model, including surface albedo, surface emissivity, roughness length, minimum stomatal
resistance, leaf area index, vapour pressure deficit factor, solar insolation factor and the Clapp–Hornberger soil parameter.
Upscaling laws were developed that map the mean and standard deviation of the distributed land-surface parameters at the subgrid
scale to their corresponding effective parameter at the grid scale. Both linear and bi-parabolic upscaling laws were obtained
for the roughness length. The bi-parabolic upscaling law fitted best for the remaining land-surface parameters, except surface
albedo and emissivity, which were best fitted with linear upscaling laws. 相似文献
2.
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
3.
The surface albedo and the surface roughness for forested areas with snow on the ground are expressed in terms of the tree silhouette parameter s, the projection on the vertical plane of trees per unit area. The absorption of insolation (direct solar beam) is quantitatively described for a horizontal snow surface with vertical tree trunks, stressing the role of the bark at snow level as triggering the snow melt.Measurement of s by field sampling in two forested sites in central Switzerland yielded values ranging from 1.8 to 2.1.Currently at Code 623 NASA/GSFC, Greenbelt, MD U.S.A. 相似文献
4.
The air flow above breaking monochromatic Stokes waves is studied using a numerical nonlinear model of the turbulent air flow above waves of finite amplitude. The breaking event (spilling breaker) is parameterized by increasing the local roughness at the downwind slope of the wave, just beyond the crest. Both moderate slope waves and steep waves are considered. Above steep breaking waves, a large increase (typically 100%) in the total wind stress — averaged over the wave profile — is found compared to nonbreaking moderate slope waves. This is due to the drastic increase of the form drag, which arises from the asymmetrical surface pressure pattern above breaking waves. Both increase of wave slope (sharpening of the crest) and increase of local roughness in the spilling breaker area cause this asymmetrical surface pressure pattern. A comparison of the numerical results with the recent experimental measurements of Banner (1990) is carried out and a good agreement is found for the structure of the pressure pattern above breaking waves and for the magnitude of enhanced momentum transfer.
Also: Dept. of Applied Physics, Techn. Univ. Delft, Netherlands. 相似文献
5.
Guy Schurgers Uwe Mikolajewicz Matthias Gröger Ernst Maier-Reimer Miren Vizcaíno Arne Winguth 《Climate Dynamics》2007,29(4):357-373
Transient experiments for the Eemian (128–113 ky BP) were performed with a complex, coupled earth system model, including
atmosphere, ocean, terrestrial biosphere and marine biogeochemistry. In order to investigate the effect of land surface parameters
(background albedo, vegetation and tree fraction and roughness length) on the simulated changes during the Eemian, simulations
with interactive coupling between climate and vegetation were compared with additional experiments in which these feedbacks
were suppressed. The experiments show that the influence of land surface on climate is mainly caused by changes in the albedo.
For the northern hemisphere high latitudes, land surface albedo is changed partially due to the direct albedo effect of the
conversion of grasses into forest, but the indirect effect of forests on snow albedo appears to be the major factor influencing
the total absorption of solar radiation. The Western Sahara region experiences large changes in land surface albedo due to
the appearance of vegetation between 128 and 120 ky BP. These local land surface albedo changes can be as much as 20%, thereby
affecting the local as well as the global energy balance. On a global scale, latent heat loss over land increases more than
10% for 126 ky BP compared to present-day. 相似文献
6.
G. Schauberger 《Theoretical and Applied Climatology》1992,46(1):45-51
Summary A model for biologically-effective ultraviolet radiation (UVR) of the sun is described, which allows the calculation of diffuse irradiance on inclined surfaces. A model is presented, for which isotropic scattered and reflected radiance are assumed. Using the horizon as a borderline between the upper and lower hemisphere, the scattering phenomena in the atmosphere for UVR are discussed. In contrast to models for other solar spectral ranges, the radiation field of UVR is close to isotropic. Only the horizon darkening by the long optical pathlengths was included in the model. This term was quantified by the UV albedo.Dedicated to O. Univ.-Prof. Dr. F. Steinhauser.With 1 Figure 相似文献
7.
The effect of orbitally induced insolation changes on Antarctic sea-ice cover are examined by means of a dynamic-thermodynamic seaice model. Results are compared with modified CLIMAP 18 000 B.P. sea-ice reconstructions. Calculations suggest that changes in insolation receipt had only a minor influence on Pleistocene sea-ice distributions. The small response can be explained by a number of factors: albedo effects reduce the insolation perturbation at the surface; some of the shortwave radiation entering the ocean contributes to bottom ablation rather than lateral melting; the radiation perturbation at the upper surface of the ice must go to warming the surface to the melting point before melting ensues; and, finally, the relatively high heat capacity of open water dampens the surface temperature response to altered seasonal insolation perturbations. 相似文献
8.
This study describes the first order impacts of incorporating a complex land-surface scheme, the bare essentials of surface transfer (BEST), into the Australian Bureau of Meteorology Research Centre (BMRC) global atmospheric general circulation model (GCM). Land seasonal climatologies averaged over the last six years of integrations after equilibrium from the GCM with BEST and without BEST (the control) are compared. The modeled results are evaluated with comprehensive sources of data, including the layer-cloud climatologies from the international satellite cloud climatology project (ISCCP) data from 1983 to 1991 and the surface-observed global data of Warren et al., a five-year climatology of surface albedo estimated from earth radiation budget experiment (ERBE) top-of-the-atmosphere (TOA) radiatioe fluxes, global grid point datasets of precipitation, and the climatological analyses of surface evaporation and albedo. Emphasis is placed on the surface evaluation of simulations of landsurface conditions such as surface roughness, surface albedo and the surface wetness factor, and on their effects on surface evaporation, precipitation, layer-cloud and surface temperature. The improvements due to the inclusion of BEST are: a realistic geographical distribution of surface roughness, a decrease in surface albedo over areas with seasonal snow cover, and an increase in surface albedo over snow-free land. The simulated reduction in surface evaporation due, in part, to the biophysical control of vegetation, is also consistent with the previous studies. Since the control climate has a dry bias, the overall simulations from the GCM with BEST are degraded, except for significant improvements for the northern winter hemisphere because of the realistic vegetation-masking effects. The implications of our results for synergistic developments of other aspects of model parameterization schemes such as boundary layer dynamics, clouds, convection and rainfall are discussed. 相似文献
9.
The variations of albedo and absorptivity of the snow cover are considered caused by the presence of the snow roughness in
the form of sastrugi. The numerical modeling is carried out within the framework of statistical approach based on the analytic
averaging of the radiative transfer equation and statistically homogeneous model on the basis of Poisson flows of points at
the straight lines. The estimates of the influence of 3D-effects of the rough surface are represented depending on optical
and geometrical characteristics of sastrugi and on the illumination conditions. It is demonstrated that if the absorption
by the snow particles is weak (the single scattering albedo w = 0.9999) the reflection of radiation by snow decreases by ∼ 2–3% when the sastrugi appear. This effect is more significant
in near infrared spectral region where w is below 0.99. 相似文献
10.
The radiative energy exchange between arctic sea-ice and stratiform clouds is studied by means of aircraft measurements and a two-stream radiation transfer model. The data have been obtained by flights of two identically instrumented aircraft during the Radiation and Eddy Flux Experiments REFLEX I in autumn 1991 and REFLEX II in winter 1993 over the arctic marginal ice zone of Fram Strait. The instrumental equipment comprised Eppley pyranometers and pyrgeometers, which measure the solar and terrestrial upwelling and downwelling hemispheric radiation flux densities, and a line-scan-camera on one aircraft to monitor the surface structure of the sea-ice. An empirical parametrization of the albedo of partly ice-covered ocean surfaces is obtained from the data, which describes the albedo increasing linearly with the concentration of the snow-covered sea-ice and with the cosine of the sun zenith angle at sun elevations below 10°. Cloud optical parameters, such as single scattering albedo, asymmetry factor and shortwave and longwave height-dependent extinction coefficient are determined by adjusting modeled radiation flux densities to observations. We found significant influence of the multiple reflection of shortwave radiation between the ice surface and the cloud base on the radiation regime. Consistent with the data, a radiation transfer model shows that stratus clouds of 400 m thickness with common cloud parameters may double the global radiation at the surface of sea-ice compared to open water values. The total cloud-surface-albedo under these circumstances is 30% larger over sea-ice than over water. Parametrizations of the global and reflected radiation above and below stratus clouds are proposed on the basis of the measurements and modeling. The upwelling and downwelling longwave emission of stratus clouds with thicknesses of more than 500 m can be satisfactorily estimated by Stefan's law with an emissivity of nearly 1 and when the maximum air temperature within the cloud is used. 相似文献
11.
12.
Drag of the sea surface 总被引：6，自引：1，他引：6
It is shown how the drag of the sea surface can be computed from the wind speed and the sea state. The approach, applicable both for fully developed and for developing seas, is based on conservation of momentum in the boundary layer above the sea, which allows one to relate the drag to the properties of the momentum exchange between the sea waves and the atmosphere.The total stress is split into two parts: a turbulent part and a wave-induced part. The former is parameterized in terms of mixing-length theory. The latter is calculated by integration of the wave-induced stress over all wave numbers. Usually, the effective roughness is given in terms of the empirical Charnock relation. Here, it is shown how this relation can be derived from the dynamical balance between turbulent and wave-induced stress. To this end, the non-slip boundary conditions is assigned to the wave surface, and the local roughness parameter is determined by the scale of the molecular sublayer.The formation of the sea drag is then described for fully developed and developing seas and for light to high winds.For the Charnock constant, a value of about 0.018–0.030 is obtained, depending on the wind input, which is well within the range of experimental data.It is shown that gravity-capillary waves with a wavelength less than 5 cm play a minor role in the momentum transfer from wind to waves. Most of the momentum is transferred to decimeter and meter waves, so that the drag of developing seas depends crucially on the form of the wave spectrum in the corresponding high wavenumber range.The dependence of the drag on wave age depends sensitively on the dependence of this high wavenumbertail on wave age. If the tail is wave-age independent, the sea drag appears to be virtually independent of wave age. If the tail depends on wave age, the drag also does. There is contradictory evidence as to the actual dependence. Therefore, additional experiments are needed.The investigation was in part supported by the Netherlands Geosciences Foundation (GOA) with financial aid from the Netherlands Organization for Scientific Research (NWO). 相似文献
13.
Partial control of climate by the biosphere may be possible through a chain of processes that ultimately links marine plankton production of dimethylsulfide (DMS) with changes in cloud albedo (Charlson et al., 1987). Changes in cloud optical properties can have profound impacts on atmospheric radiation transfer and, hence, the surface environment. In this study, we have developed a simple model that incorporates empirically based parameterizations to account for the biological control of cloud droplet concentration in a first attempt to estimate the strength of the DMS-cloud albedo feedback mechanism. We find that the feedback reduces the global climatic response to imposed perturbations in solar insolation by less than 7%. Likewise, it modifies the strength of other feedbacks affecting surface insolation over oceans by roughly the same amount. This suggests that the DMS-cloud albedo mechanism will be unable to substantially reduce climate sensitivity, although these results should be confirmed with less idealized models when more is known about the net production of DMS by the marine biosphere and its relation to aerosol/cloud microphysics and climate. 相似文献
14.
A method has been developed to determine the surface albedo over the Qinghai-Xizang Plateau region from NOAA polar orbiter AVHRR (Advanced Very High Resolution Radiometer) data. The empirical rela-tionship between clear-sky planetary and surface albedos is established the basis of surface global radiation measurements and the specified ratio between atmospheric reflection and absoption of solar radiation. The method is applied to the Qinghai-Xizang region with several measurements during the period of Sep. to Nov., 1985. A comparison is presented between the estimated surface albedos and that of surface observation. The results show that the presented method is suitable to detecting the spatial and temporal variation of surface albedo and is relevant for climatologies studies. The possible error sources and improvements are discussed as well. 相似文献
15.
To build land surface dataset for climate model,with application of remote sensing technique as well as the Geographic Information System(GIS),the data of surface type,roughness and albedo over China in 1997 were retrieved,resolutions being 10 km×10 km.Based on these data,an analysis is conducted on the geographic distributions and seasonal variations of surface vegetation cover and roughness as well as albedo over China.Results show that surface vegetation cover is mainly located to the south of Yangtze River,in Southwest and Northeast China andsparse vegetation cover is in the Northwest.The variation of land surface cover affects the variations of land surface roughness and albedo.High albedo occurred in the north of Xinjiang Autonomous Region,the north of Northeast China and the Qinghai-Xizang Plateau in winter,in correspondence with the location of snow cover.For most part of China,surface roughness decreases and albedo increases in winter,while the roughness increases and the albedo decreases in summer,which could mainly result from land surface cover(snow cover and vegetation cover)and soil moisture changes.This shows that the geographic distribution and seasonal variation of the albedo are almost opposite to those of the roughness,in agreement with theoretical results.Temporally,the amplitude of surface roughness change is quite small in comparison with the roughness itself. 相似文献
16.
Late Quaternary humidity changes resulted in substantial modifications of the land surface characteristics in the Altiplano
of the Atacama Desert, central Andes. Reconstructions of surface albedo, top-of-atmosphere (TOA) albedo, and short-wave net
radiation in the Andes of northern Chile for 20, 14, 10, 7 and 0 ka suggest that surface and TOA albedo increased substantially
during periods of relatively humid environmental conditions (i.e., with large palaeolakes, glaciers and dense vegetation).
The decrease of summer shortwave net radiation and seasonality during the late-glacial/early Holocene humid phase (14 to 10 ka)
due to Earth’s surface and atmospheric characteristics added to the effect of orbitally driven negative deviations of Southern
Hemisphere austral summer insolation and minimum seasonality at 20 °S. Therefore, in situ radiative forcing is, in contrast
to the Northern Hemisphere tropics, not a suitable explanation for enhanced convective precipitation and, ultimately, humid
climatic conditions. Our results suggest that late Quaternary humidity changes on the Altiplano reflect a collective response
to (1) environmental changes in the source area of the moisture (e.g., re-expansion of the rain forest and increased release
of latent heat over Amazonia and the Chaco, warm sea surface temperatures in the E Pacific) and, (2) large-scale circulation
patterns and wave structures in the upper troposphere (strength and position of the Bolivian High, divergent flow stimulating
convection over the Altiplano), or that they even reflect a response to (3) interhemispherical teleconnections.
Received: 6 October 1997 / Accepted: 20 May 1998 相似文献
17.
Summary The dependency of erythemal weighted solar UV irradiance on tilted surfaces with different orientation is investigated with respect to solar zenith angle, variable atmospheric conditions and albedo of the location. For overcast conditions or a cloud in front of the sun, the irradiance on a horizontal surface in general is largest, with the consequence that it is reduced for surfaces with any tilted position. For cloud free conditions the irradiance on a tilted plane, in comparison to that on a horizontal flat surface, is increased for orientations towards the sun, but reduced for other orientations. The increase is strongest for low sun in combination with clear atmosphere and high ground albedo, as is typical for snow covered mountain conditions. 相似文献
18.
Despite its importance for momentum and mass transfer across the air–sea interface, the dynamics of airflow over breaking
waves is largely unknown. To fill this gap, velocity and vorticity distributions above short-gravity breaking waves have been
measured in a wind-wave tank. A Digital Particle Image velocimetry technique (DPIV) was developed to accomplish these measurements
above single breaking waves, propagating in mechanically-generated wave groups and forced by the wind. By varying the wind
speed and initial characteristics of the groups, the airflow structure was captured over waves at different stages of the
breaking process, and breaking with various intensities. The instantaneous airflow that separates from a sharp breaking crest
is very similar to that occurring over a backward facing step. The separation bubble is however strongly unsteady: the steeper
the wave crest and the larger the Reynolds number based on the crest-height, the higher the separated layer and the farther
downwind the reattachment point. Instantaneous flow topology displays specific features of three-dimensional separation patterns.
The tangential stress above the wave profile does not exhibit spikes at reattachment but grows progressively downwind from
zero at reattachment to a value at the next crest approximately that found at the upwind breaking crest. Static pressure measurements
revealed that large pressure falls are generated by vortices in the separated layer, as found in separated flows over solids.
This study may provide useful data for theoretical and numerical modelling of the flow and associated phenomena. 相似文献
19.
The influence of low surface roughness of deserts on the July circulation is examined by employing numerical simulations with a GLAS GCM. Two identical sets of simulations were made with the model starting from the initial state of the atmosphere based on the NMC analysis of observations for June 15, at OOZ for the years 1979 and 1980. The first set, called the Control, had land surface roughness set to 45 cm, everywhere. The second set called the Experiment, had surface roughness set to 0.02 cm for deserts, but 45 cm everywhere else on land. All other prescribed boundary conditions were the same in both runs.A comparative analysis of these simulations showed that the rainfall in the Sahara desert was reduced significantly in both Experiments as compared to the corresponding Controls; the ITCZ (inter-tropical convergence zone) moved southward, to about 14° N, which is close to its observed location at about 10° N. This was primarily caused by the relative moisture divergence from the smoother Sahara. In other deserts, which anyway had little rainfall in the July simulation of the Control run, there was virtually no change. The differences in regional heat and moisture budgets, particularly for the Sahara desert, are significant as compared to the sample standard deviation for a set of three July simulations (i.e., Control runs for three different initial conditions). In a third simulation, in which the surface roughness was changed over all land, similar results were obtained in the Sahara desert region.The study reveals the influence of low surface-roughness of deserts on the July rainfall. For the Sahara desert, this influence is comparable to that of an increase in surface albedo. In nature, formation of deserts leads to reduction of surface roughness as the vegetation perishes and soil erosion ensues. It is inferred that the smoothness of land then causes reduction in rainfall and further promotes desertification.Sigma Data Services through contract # NASA 25900. 相似文献
20.
H. Tooming 《Theoretical and Applied Climatology》2002,72(3-4):165-172
Summary ?The dependence of global and diffuse radiation on surface albedo due to multiple reflection of radiation between the surface
and the atmosphere (base of clouds) is found on the basis of data obtained at the Tartu–T?ravere Actinometric Station over
the period 1955–2000. It is found that the monthly totals of global radiation increase by up to 1.38–1.88 times, particularly
in the winter half-year between November and March, when snow cover albedo may be high. A semi-empirical formula is derived
for calculating with sufficient accuracy the monthly totals of global radiation, considering the amount of cloudiness and
the surface albedo. In the time series of the monthly total by global radiation a downward trend occurs in winter months.
A decrease in global radiation by up to 20% in the past 46 years can be explained primarily by a relatively high negative
trend in the snow cover duration and surface albedo (up to − 0.24). As a result, days are growing darker, a new phenomenon
associated with climate change, which undoubtedly affects human mood to some extent.
Received November 8, 2001; revised January 24, 2002; accepted February 2, 2002 相似文献