Reflection Of Solar Radiation Research Articles

Tropospheric Water Vapor and Climate Sensitivity

Estimates are made of the effect of changes in tropospheric water vapor on the climate sensitivity to doubled carbon dioxide (CO2), using a coarse resolution atmospheric general circulation model coupled to a slab mixed layer ocean. The sensitivity of the model to doubled CO2 is found as the difference between the equilibrium responses for control and doubled CO2 cases. Clouds are specified to isolate the water vapor feedback. Experiments in which the water vapor distribution is specified rather than internally calculated are used to find the contribution of water vapor in various layers and latitude belts to the sensitivity. The contribution of water vapor in layers of equal mass to the climate sensitivity varies by about a factor of 2 with height, with the largest contribution coming from layers between 450 and 750 mb, and the smallest from layers above 230 mb. The positive feedback on the global mean surface temperature response to doubled CO2 from water vapor above 750 mb is about 2.6 times as large as that from water vapor below 750 mb. The feedback on global mean surface temperature due to water vapor in the extratropical free troposphere (above 750 mb) is about 50% larger than the feedback due to the lower-latitude free troposphere water vapor. Several important sources of nonlinearity of the radiative heating rates were identified in the process of constructing the specified cloud and water vapor fields. These are (i) the interaction of clouds and solar radiation, which produces much more reflection of solar radiation for time mean clouds than for the instantaneous clouds;(ii) the correlation of clouds and water vapor, which produces less downward longwave radiation at the ground for correlated clouds and water vapor than when these fields are independent; and (iii) the interaction of water vapor with longwave radiation, which produces less downward longwave radiation at the ground for the average over instantaneous water vapor distributions than for the time mean water vapor distribution.

Diurnal and Semidiurnal Tides in Global Surface Pressure Fields

Global surface pressure data from 1976 to 1997 from over 7500 land stations and the Comprehensive Ocean‐ Atmosphere Data Set have been analyzed using harmonic and zonal harmonic methods. It is found that the diurnal pressure oscillation (S1) is comparable to the semidiurnal pressure oscillation ( S2) in magnitude over much of the globe except for the low-latitude open oceans, where S2 is about twice as strong as S1. Over many land areas, such as the western United States, the Tibetan Plateau, and eastern Africa, S1 is even stronger than S2. This is in contrast to the conventional notion that S2 predominates over much of the globe. The highest amplitudes (;1.3 mb) of S1 are found over northern South America and eastern Africa close to the equator. Here S1 is also strong (;1.1 mb) over high terrain such as the Rockies and the Tibetan Plateau. The largest amplitudes of S2 (;1.0‐1.3 mb) are in the Tropics over South America, the eastern and western Pacific, and the Indian Ocean. Here S1 peaks around 0600‐0800 LST at low latitudes and around 1000‐1200 LST over most of midlatitudes, while S2 peaks around 1000 and 2200 LST over low- and midlatitudes. Here S1 is much stronger over the land than over the ocean and its amplitude distribution is strongly influenced by landmasses, while the land‐sea differences of S2 are small. The spatial variations of S1 correlate significantly with spatial variations in the diurnal temperature range at the surface, suggesting that sensible heating from the ground is a major forcing for S1. Although S2 is much more homogeneous zonally than S1, there are considerable zonal variations in the amplitude of S2, which cannot be explained by zonal variations in ozone and water vapor. Other forcings such as those through clouds’ reflection and absorption of solar radiation and latent heating in convective precipitation are needed to explain the observed regional and zonal variations in S2. The migrating tides and 1 S 1 predominate over other zonal wave components. However, the nonmigrating tides are substantially stronger 2 S 2 than previously reported. The amplitudes of both the migrating and nonmigrating tides decrease rapidly poleward with a slower pace at middle and high latitudes.

Earth‐average temperature: A time delay approach

Earth‐average temperature is investigated using a simple energy balance model of the Budyko‐Sellers‐Ghil type expressed as a delay‐differential equation describing the absorption and reflection of incoming solar radiation and surface‐reflected infrared radiation. Cloud albedos for both radiations and the surface albedo as affected by ice coverage are assumed to depend upon the temperature that existed some time ago, introducing a time delay into the model. A variety of steady and oscillatory states are possible for Earth‐average temperature, assuming plausible functions for the albedos, blackbody cooling, and suitable delay times. Multiple true steady states and multiple transient pseudo steady states as well as periodic, chaotic, and square‐wave relaxation‐oscillations result, The bifurcation structure relating the appearance of these phenomena to system parameters is explored. This very simple climate model exhibits complex behavior in global temperature without solar variation or environmental perturbation. Bifurcations exist at which small changes in parameters lead to destabilization of steady states and dramatic changes in qualitative behavior.

Retrieving land surface reflectances using the ATSR‐2: A theoretical study

The measurement of absolute land reflectance from Earth‐orbiting satellites requires the separation of the signal due to the reflection of solar radiation by the surface from that due to scattering by the atmosphere. Thus for accurate but generally applicable quasi‐operational retrieval techniques it is necessary to derive atmospheric parameters, such as the aerosol type and loading, simultaneously with the surface reflectances. The assumption of large‐scale horizontal homogeneity across an image, or the presence of very low reflectance pixels within an image, is avoided, since these are not necessarily applicable in the general case. In this paper, results of simulated retrievals using the visible and near‐infrared channels of the ATSR‐2 satellite radiometer are presented on the basis of techniques which exploit the dual look and other features of the instrument. The pixel‐based retrieval scheme comprises a fast representation of atmospheric scattering and a simple surface reflectance approximation. The effect of the atmospheric approximation on the accuracy of retrieval of the surface reflectance and atmospheric optical depth is tested by using a full multiple‐scattering radiative transfer model with simpler surface model. The effect on retrieval accuracy of the surface model is tested using a full surface vegetation canopy reflectance model with inclusion of the hot‐spot effect, combined with a successive orders of scattering atmospheric radiative transfer model, taken to second order. The results indicate that the scheme could provide accurate retrieval of surface reflectances even where no extraneous information on the surface bidirectional reflectance or on the atmospheric optical thickness is available. The scheme is also applicable to the AATSR instrument to be launched on the ENVISAT (Environmental Satellite) and, more widely, to other satellite radiometers with multiple views of the Earth's surface.

The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation

Abstract. The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.

Relationship between Cloud Radiative Forcing and Sea Surface Temperatures over the Entire Tropical Oceans

Abstract Satellite measurements from January 1985 to December 1989 show that warmer tropical oceans as a whole are associated with less longwave greenhouse effect of clouds and less cloud reflection of solar radiation to the space. The regression slopes of longwave and shortwave cloud radiative forcings against sea surface temperatures averaged from 30°N to 30°S are about −3 and 2 W m−2 K−1, respectively. Relationships of cloud forcings and sea surface temperatures are analyzed for regions with different sizes. As has been reported in previous studies, the magnitude of area-averaged cloud radiative forcing for both longwave and shortwave radiations increases with sea surface temperatures in the equatorial eastern Pacific and is insensitive to sea surface temperatures over the tropical Pacific basin. Yet, when the region extends beyond the tropical Pacific, the magnitude decreases with sea surface temperatures. This phenomenon is shown to relate to changes in clouds over the tropical Indian Ocean and Atlan...

Feasibility of an Iodine Gas Laser Pumped by Concentrated Terrestrial Solar Radiation

The present work demonstrates the feasibility of a t-C{sub 4}F{sub 9}I iodine gas laser pumped by concentrated terrestrial solar radiation. Iodine gas lasers have advantages when compared to solid-state systems. They pump at low concentration ({approximately}100 suns, as compared to 45,000 suns for the most efficient solid-state lasers; Cooke, 1992), and thus do not require expensive, optical-grade concentration systems. The lasant medium (iodine gas) is easily cooled by flowing the lasant medium, while solid-state lasers require complicated cooling apparatus to avoid crystal fracture from thermal gradients. Finally, a gas laser is easily upsized, as the iodine gas will expand to fill any oscillation cavity. Solid-state lasers are limited by the size of the crystal that can be grown and cooled, and the higher efficiency comes at the cost of the very high solar concentration requirements. The iodine gas under consideration has a smaller overlap with the terrestrial solar spectrum than solid state lasers, and therefore has a lower efficiency. However, comparison of relative efficiencies should also include cost estimates of highly specialized optical equipment (such as sapphire CPC`s), cooling requirements (liquid nitrogen baths), and losses due to blockage of the chopper wheel. Such simplistic comparisons as ratio of power outmore » to solar power in are misleading, as they contain the implicit assumption that solar energy must be purchased, as are fossil fuels. In reality, the solar energy is free, and the true expense is the manufacture and degree of sophistication required of the solar radiation reflection system, and the cooling system.« less

The whitehouse effect—Shortwave radiative forcing of climate by anthropogenic aerosols: an overview

Loadings of tropospheric aerosols have increased substantially over the past 150 yr as a consequence of industrial activities. These aerosols enhance reflection of solar radiation by the Earth-atmosphere system both directly, by scattering light in clear air and, indirectly, by increasing the reflectivity of clouds. The magnitude of the resultant decrease in absorption of solar radiation is estimated to be comparable on global average to the enhancement in infrared forcing at the tropopause due to increases in concentrations of CO 2 and other greenhouse gases over the same time period. Estimates of the aerosol shortwave forcing are quite uncertain, by more than a factor of two about the current best estimates. This article reviews the atmospheric chemistry and microphysical processes that govern the loading and light scattering properties of the aerosol particles responsible for the direct effect and delineates the basis for the present estimates of the magnitude and uncertainty in the resultant radiative forcing. The principal sources of uncertainty are in the loading of anthropogenic aerosols, which is highly variable spatially and temporally because of the relatively short residence time of these aerosols (ca. 1 week) and the episodic removal in precipitation, and in the dependence of light scattering on particle size, and in turn on relative humidity. Uncertainty in aerosol forcing is the greatest source of uncertainty in radiative forcing of climate over the industrial period. At the high end of the uncertainty range, the aerosol forcing is comparable to the anthropogenic greenhouse forcing, and substantially greater in industrialized regions. Even at the low end of the range, the aerosol forcing cannot be neglected in considerations of influences on climate over the industrial period. This uncertainty greatly limits the ability to draw empirical inferences of climate sensitivity to radiative forcing.

Diffuse reflection and transmission of solar radiation by a finite atmosphere bounded by a reflecting surface

The problem of diffuse reflection and transmission of solar radiation through a planetary atmosphere bounded from below by a reflecting surface is solved. The solution method based on rewriting the solution of the proposed problem in terms of the well known standard problem solution, where the planetary surface does not reflect. The solution of the standard problem can be found elsewhere or as we did by using the maximum entropy method. Numerical results for the angular radiation intensity and for the reflection and transmission coefficients are presented and compared with those obtained by Chandrasekhar's method.

The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation

<strong class="journal-contentHeaderColor">Abstract.</strong> The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.

Plant and soil influences on estimating biomass of wheat in plant breeding plots using field spectral radiometers

Field spectral radiometers were used to estimate the biomass of wheat at early growth stages, as wheat breeders require a rapid, non-destructive technique to rank wheat genotypes for early vigour. Under experimental conditions, good relationships were obtained between reflectance and biomass prior to the wheat crop achieving a green area index of 1.5. When used above different soil types, good results were achieved on very uniform dark and light soils under experimental conditions, but greater differentiation between plots differing in biomass was achieved on darker soils. Similarly, under operational conditions in wheat breeders' plots, the best results were achieved against a dark soil background. Structural differences between plants also influenced solar radiation reflectance. At the Merredin site with the dark soil background, where the best correlation between reflectance and biomass was achieved, the relationship was much stronger for the more uniform genotypes at the second stage of selection than for the more heterogeneous genotypes at the first stage of selection. On these plots, the vegetation spectral indices NDVI (normalised difference vegetation index) and TSAVI (transformed soil-adjusted vegetation index) had a coefficient of determination 90-95% as good as the best regression using two wavebands. To optimise the field spectroradiometry technique for estimating early biomass, it should be applied at a weed-free site, with a uniform dark soil background and on material that is relatively homogenous in structure. We conclude that, unless these precautions are taken, the technique will have limited utility in breeding programs.

Diurnal asymmetry of climatic response to increased CO2 and aerosols: Forcings and feedbacks

To examine the causes of the observed diurnally asymmetrical climate change over land, the roles of different physical mechanisms are evaluated using a radiative‐convective model of the diurnal cycle. This model explicitly calculates a complete set of physical processes, including the water vapor distribution, clouds, transports in the turbulent boundary layer, and convection. Calculations were carried out for midlatitude summer and winter and for tropical spring conditions taking into account the most important climate forcings: CO2 increase, tropospheric aerosol pollution, and the combined case with simultaneous CO2 and aerosol effects. We find that feedbacks in the climate system are more important than forcings in producing diurnal asymmetry. The water vapor shortwave feedback dominates the diurnal distribution of the response. For all cases with warming, the diurnal temperature range (DTR) decreases, not due to the greenhouse effect of water vapor, but as a result of more intensive absorption of the solar radiation in the near infrared by water vapor and cloud water in a warmer, wetter climate independent of the type of forcing. Aerosol reflection and absorption of solar radiation cool the surface and decrease DTR directly, but the negative daytime water vapor feedback virtually cancels out the diurnal asymmetry. In the combined case, with a 50% CO2 content increase combined with tropospheric aerosol pollution, which is not far from the current observed conditions over land, the greenhouse warming raises the temperature enough that the direct aerosol effect decreases the DTR. In all cases the time and spatial redistribution of clouds have a significant impact on the climate sensitivity and diurnal cycle. As in the observations, increasing of cloudiness and water vapor content occurs with decreasing of the DTR. In our model the cloudiness and water vapor changes are produced by the same forcings that lower the DTR; they are not independent causes of changes of the DTR, but rather are important internal feedback mechanisms.

Reflection of solar radiation by the Antarctic snow surface at ultraviolet, visible, and near‐infrared wavelengths

The variation of snow albedo with wavelength across the solar spectrum from 0.3 μm in the ultraviolet (UV) to 2.5 μm in the near infrared (IR) was measured at Amundsen‐Scott South Pole Station during the Antarctic summers of 1985–1986 and 1990–1991. Similar results were obtained at Vostok Station in summer 1990–1991. The albedo has a uniformly high value of 0.96–0.98 across the UV and visible spectrum, nearly independent of snow grain size and solar zenith angle, and this value probably applies throughout the interior of Antarctica. The albedo in the near IR is lower, dropping below 0.15 in the strong absorption bands at 1.5 and 2.0 μm; and it is quite sensitive to grain size and somewhat sensitive to zenith angle. Near‐IR albedos were slightly lower at Vostok than at South Pole, but day‐to‐day variations in the measured grain size due to precipitation, drifting, and metamorphism were found to cause temporal variations in near‐IR albedo larger than those due to any systematic geographical change from South Pole to Vostok. The spectrally averaged albedos ranged from 0.80 to 0.85 for both overcast and clear skies, in agreement with measurements by others at South Pole and elsewhere in Antarctica. Using a two‐layer radiative transfer model, the albedo can be explained over the full wavelength range. Tests were made to correct for systematic errors in determining spectral albedo. Under clear skies at about 3000‐m elevation the diffuse fraction of downward irradiance varied from 0.4 in the near UV to less than 0.01 in the near IR; knowledge of this fraction is required to correct the measured irradiance for the instrument's deviation from a perfect cosine‐response. Furthermore, the deviation from cosine response is itself a function of wavelength. Under clear skies a significant error in apparent albedo can result if the instrument's cosine collector is not parallel to the surface; e.g., if the instrument is leveled parallel to the horizon, but the local snow surface is not horizontal. The soot content of the snow upwind of South Pole Station was only 0.3 ng/g. It was somewhat greater at Vostok Station but was still too small to affect the albedo at any wavelength. Bidirectional reflectance at 0.9‐μm wavelength, measured from a 23‐m tower at the end of summer after the sastrugi (snow dunes) had diminished, showed a pattern remarkably similar to the spectrally averaged pattern obtained from the Nimbus 7 satellite.

A Rapid Radiative Transfer Model for Reflection of Solar Radiation

A rapid analytical radiative transfer model for reflection of solar radiation in plane-parallel atmospheres is developed based on the Sobolev approach and the delta function transformation technique. A distinct advantage of this model over alternative two-stream solutions is that in addition to yielding the irradiance components, which turn out to be mathematically equivalent to the delta-Eddington approximation, the radiance field can also be expanded in a mathematically consistent fashion. Tests with the model against a more precise multistream discrete ordinate model over a wide range of input parameters demonstrate that the new approximate method typically produces average radiance differences of less than 5%, with worst average differences of approximately 10%-15%. By the same token, the computational speed of the new model is some tens to thousands times faster than that of the more precise model when its stream resolution is set to generate precise calculations.

Solar cells and batteries with unusual selective coatings for combined supply of heat and electricity by solar power stations

Abstract Optical coatings are used to increase the efficiency, extend the life, and to improve the electrophysical characteristics and stability of solar energy converters based on various physical principles, including semiconductor solar cells. When solar cells are placed on the exterior of collectors in photothermal systems, and generate both electric and thermal power, the optical coating applied to their surfaces gives them highly unusual selective properties, namely, reduced reflection of solar radiation (and high transparency in this part of the spectrum), which leads to higher integrated solar absorption coefficient, and enhanced infrared reflection which ensures that the thermal emission coefficient is as low as possible. Solar cells then not only generate electric power but, at the same time, covered by these coatings, act as selective optical surfaces for solar collectors.

Effect of Amazon Smoke on Cloud Microphysics and Albedo-Analysis from Satellite Imagery

NOAA Advanced Very High Resolution Radiometer images taken over the Brazilian Amazon Basin during the biomass burning season of 1987 are used to study the effect of smoke aerosol particles on the properties of low cumulus and stratocumulus clouds. The reflectance at a wavelength of 0.64 µm and the drop size, derived from the cloud reflectance at 3.75 µm, are studied for tens of thousands of clouds. The opacity of the smoke layer adjacent to each cloud is also monitored simultaneously. Though from satellite data it is impossible to derive all the parameters that influence cloud properties and smoke–cloud interaction (e.g., detailed aerosol particles size distribution and chemistry, liquid water content, etc.); satellite data can be used to generate large-scale statistics of the properties of clouds and surrounding aerosol (e.g., smoke optical thickness, cloud-drop size, and cloud reflection of solar radiation) from which the interaction of aerosol with clouds can be surmised. In order to minimize the effect of variations in the precipitable water vapor and in other smoke and cloud properties, biomass burning in the tropics is chosen as the study topic, and the results are averaged for numerous clouds with the same ambient smoke optical thickness. It is shown in this study that the presence of dense smoke (an increase in the optical thickness from 0.1 to 2.0) can reduce the remotely sensed drop size of continental cloud drops from 15 to 9 µm. Due to both the high initial reflectance of clouds in the visible part of the spectrum and the presence of graphitic carbon, the average cloud reflectance at 0.64 µm is reduced from 0.71 to 0.68 for an increase in smoke optical thickness from 0.1 to 2.0. The measurements are compared to results from other years, and it is found that, as predicted, high concentration of aerosol particles causes a decrease in the cloud-drop size and that smoke darkens the bright Amazonian clouds. Comparison with theoretical computations based on Twomey's model show that by using the measured reduction in the cloud-drop size due to the presence of smoke it is possible to explain the reduction in the cloud reflectance at 0.64 µm for smoke imagery index of −0.02 to −0.03. Smoke particles are hygroscopic and have a similar size distribution to maritime and anthropogenic sulfuric aerosol particles. Therefore, these results may also be representative of the interaction of sulfuric particles with clouds.

A solar reflecting material for radiative cooling applications: ZnS pigmented polyethylene

Abstract Plastic foils containing nonabsorbing pigments can display a high reflectance of solar radiation combined with a high transmittance in the atmospheric window region in the thermal infrared. Such foils can be applied as selective covers enabling radiative cooling of an underlying material during the night and avoiding heating in direct sunlight during the day. The foils could be used for condensing water or cooling food, buildings, etc. We have prepared ZnS pigmented polyethylene foils with various thicknesses and volume fractions of pigments. The optical properties of the foils were compared with theory, and good agreement was achieved for pigment volume fractions up to 0.1. The optimum solar reflectance of the foil is 0.825 for the available pigment powder; it should be 0.88 if heating were to be avoided at noon with the sun in its zenith. The computed cooling power for a radiator covered with the best sample was 52 W m−2 at night, and the equilibrium temperature of the radiator was predicted to be 12 K below the ambient temperature. Computations showed that heating of the radiator could be avoided 18 hours per day, and the radiator temperature at noon was 8 K above the ambience.

Solar Radiative Fluxes for Broken Cloud Fields above Reflecting Surfaces

Abstract A statistical bidirectional method for including the effects of underlying reflecting surfaces in Monte Carlo simulations of atmospheric photon transport is presented. It is illustrated for the idealized Lambertian surface and a general particulate surface. It is shown that the simple Lambertian surface should be an adequate approximation (to mildly anisotropic surfaces) for calculation of overall fluxes for broken cloud fields. The problem of incorporating multiple internal reflections of solar radiation between cloud and surface is reviewed, and cloud field reflectances to upwelling radiation rk as a function of the number of internal reflections k are calculated. Unlike plane-parallel and regular arrays of cloud, all rk are generally not equal for more realistic scaling cloud fields. Strictly speaking, this prohibits use of the familiar geometric sum formulas for flux calculation in a multiple reflecting system. Fortunately, though fortuitously, the geometric sum formulas can be used in such c...

An evaluation of scale-dependent effects of atmosphere-glacier interactions on heat supply to glaciers

Scale-dependent atmosphere-glacier interactions operate over a glacier surface as the surface has different thermal and radiative characteristics from those of the surrounding ground. In order to evaluate heat supply to the glacier surface in the main ablation period, three main interaction processes are considered: advection, glacier wind, and multiple reflection of solar radiation. The amount of heat supply was calculated for the equilibrium line altitude (ELA) by assuming a simple rectangular-shaped glacier, and by applying meteorological and glaciological data for four different glaciated regions (Tien Shan, Patagonia, west Kunlun and Nepal Himalaya). The total heat supply due to the above three processes had the common tendency of being smallest for glaciers of 1 to several kilometres in length, and largest at 16 km, which was the maximum length considered in this study. Among the cases, the Tien Shan showed a daytime heat supply higher by 2.3 MJ m−2 for a 16km-long glacier compared with a small glacier 2 km in length. Relating this difference directly to ELA, an ELA approximately 300 m higher might be expected for a long glacier than a short one, assuming the same amount of solid precipitation. Glacier inventory data for China support this tendency, but the calculated value is slightly larger than that observed. The results show that there is a possibility that responses in glacier variation to climate change may be modified considerably through scale-dependent atmosphere-glacier interactions.

An evaluation of scale-dependent effects of atmosphere-glacier interactions on heat supply to glaciers

Scale-dependent atmosphere-glacier interactions operate over a glacier surface as the surface has different thermal and radiative characteristics from those of the surrounding ground. In order to evaluate heat supply to the glacier surface in the main ablation period, three main interaction processes are considered: advection, glacier wind, and multiple reflection of solar radiation. The amount of heat supply was calculated for the equilibrium line altitude (ELA) by assuming a simple rectangular-shaped glacier, and by applying meteorological and glaciological data for four different glaciated regions (Tien Shan, Patagonia, west Kunlun and Nepal Himalaya). The total heat supply due to the above three processes had the common tendency of being smallest for glaciers of 1 to several kilometres in length, and largest at 16 km, which was the maximum length considered in this study. Among the cases, the Tien Shan showed a daytime heat supply higher by 2.3 MJ m−2for a 16km-long glacier compared with a small glacier 2 km in length. Relating this difference directly to ELA, an ELA approximately 300 m higher might be expected for a long glacier than a short one, assuming the same amount of solid precipitation. Glacier inventory data for China support this tendency, but the calculated value is slightly larger than that observed. The results show that there is a possibility that responses in glacier variation to climate change may be modified considerably through scale-dependent atmosphere-glacier interactions.