Numerical Simulation of the Atmospheric Effects on Snow Albedo with a Multiple Scattering Radiative Transfer Model for the Atmosphere-Snow System

Abstract

The atmospheric effects on the spectral and spectrally integrated snow albedos at the snow surface and top of the atmosphere (TOA) are investigated. A multiple scattering radiative transfer model based on the "doubling and adding" method, combined with the Mie theory is applied to estimate the effects of absorption and scattering by atmospheric molecules, absorptive gases, aerosols and clouds.It is shown that the spectral surface albedo is reduced by the atmospheric absorptive gases at large solar zenith angles. The solar zenith angle dependence is weakened in the wavelength region shorter than 0.5um by the Rayleigh scattering, and at almost all wavelengths by the atmospheric aerosols and cloud cover. H2O rich atmosphere decreases the spectral surface albedo at large solar zenith angles in the H2O bands, while the additional reduction of downward solar flux in the near infrared region by H2O absorption causes the spectrally integrated surface albedo to increase by several percent. Aerosols increase the spectrally integrated surface albedo at small solar zenith angles and reduce it at large solar zenith angles, however they reduce the spectrally integrated planetary albedo, except at large solar zenith angles. Optically-thick cloud cover increases both the spectrally integrated surface and planetary albedos at any solar zenith angle.In the visible region at small solar zenith angles, the downward solar flux on the snow surface under cloudy sky can exceed that for the clear case, and both further exceed the extraterrestrial solar flux, resulting from the multiple reflection between snow surface and the atmosphere (cloud cover). The global solar radiation on the snow surface under cloudy sky, however, never exceeds that for the clear case and that at TOA.

Possible Effect of Anthropogenic Aerosol Deposition on Snow Albedo Reduction at Shinjo, Japan

“…The snow type and the grain size for each layer were measured at snow pits. The term ''snow grain size'' refers to the optically equivalent snow grain radius r 2 defined by Aoki et al (1998Aoki et al ( , 2000, which is defined as the half width of the branch for dendrites, or of the narrower portion for broken crystals, or of each grain for the aggregate granular grains. The snow samples were taken at the snow pits from the surface to a depth of 5 cm.…”

“…In this section, we examine the effects of the snow physical parameters on the broadband albedo by comparing the observed albedos with the theoretically calculated ones, by using the multiple scattering model of the radiative transfer for the atmosphere-snow system (Aoki et al 1999;Aoki et al 2000). The atmospheric model includes mid-latitude winter with 15 atmospheric layers (Anderson et al 1986), urban aerosols with an optical thickness of 0.2 at l ¼ 0:5 mm, and water clouds with an optical thickness of 40 at l ¼ 0:5 mm for cloudy conditions.…”

Characteristics of UV-B Irradiance at Syowa Station, Antarctica: Analyses of the Measurements and Comparison with Numerical Simulations

“…The spectral albedo of snow surface varies with snow grain size and the interaction between atmosphere and snow surface. The major modifications of the model from that used in Aoki et al (1999Aoki et al ( , 2000 are the incorporation of the model of pseudo-spherical atmosphere (Dahlback and Stamnes 1991) and the revised extraterrestrial solar radiation (WMO 1986). In the polar region the period of large solar zenith angles is generally long.…”

“…The parameters of aerosol and cloud are basically the same as Aoki et al (1999), except for the aerosol size distribution as described below. For the aerosol the effects of sulfuric acid aerosol on the spectral UV-B irradiance and UV-B irradiance are investigated for three values of aerosol optical depth, t a ¼ 0:02, 0.05 and 0.10 at l ¼ 500 nm.…”

“…In this paper we will study the effects of these factors, as well as snow grain size on surface UV-B irradiance by the theoretical model of UV-B irradiance using ARTMASS (Advanced Radiative Transfer Model for the Atmosphere-Snow System) developed by Aoki et al (1999Aoki et al ( , 2000, the analyses of measured UV-B irradiance in 1996 at Syowa Station conducted by JMA (JMA 1997) in Antarctica, and their comparisons.…”