Abstract
Abstract. In climate models, the snow albedo scheme generally calculates only a narrowband or broadband albedo, which leads to significant uncertainties. Here, we present the Versatile ALbedo calculation metHod based on spectrALLy fixed radiative vAriables (VALHALLA version 1.0) to optimize spectral snow albedo calculation. For this optimization, the energy absorbed by the snowpack is calculated by the spectral albedo model Two-streAm Radiative TransfEr in Snow (TARTES) and the spectral irradiance model Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). This calculation takes into account the spectral characteristics of the incident radiation and the optical properties of the snow based on an analytical approximation of the radiative transfer of snow. For this method, 30 wavelengths, called tie points (TPs), and 16 reference irradiance profiles are calculated to incorporate the absorbed energy and the reference irradiance. The absorbed energy is then interpolated for each wavelength between two TPs with adequate kernel functions derived from radiative transfer theory for snow and the atmosphere. We show that the accuracy of the absorbed energy calculation primarily depends on the adaptation of the irradiance of the reference profile to that of the simulation (absolute difference <1 W m−2 for broadband absorbed energy and absolute difference <0.005 for broadband albedo). In addition to the performance in terms of accuracy and calculation time, the method is adaptable to any atmospheric input (broadband, narrowband) and is easily adaptable for integration into a radiative scheme of a global or regional climate model.
Highlights
Solar irradiance is an essential source of energy to snow and ice surfaces (Warren, 1982)
We compare the simulated broadband absorbed energy resulting from VALHALLA for 30 tie points (TPs) with that obtained with Two-streAm Radiative TransfEr in Snow (TARTES)–Santa Barbara discrete ordinate radiative transfer (DISORT) Atmospheric Radiative Transfer (SBDART) for the same spectral range between 320 and 4000 nm
The efficiency of the method is compared to the TARTES–SBDART calculation for different spectral resolutions ranging from 1 nm to 100 nm
Summary
Solar irradiance is an essential source of energy to snow and ice surfaces (Warren, 1982). The albedo, defined as the fraction of reflected solar radiation, is very high for fresh snow and limits energy absorption by the snowpack. Darker or old snow and glacial ice absorb more solar energy (Warren, 1982; Gardner and Sharp, 2010). The snow spectral albedo, defined as the fraction between reflected and incident solar energy for a given wavelength (Grenfell et al, 1994), is higher for near-ultraviolet (near-UV, 300– 400 nm), visible (400–700 nm), and near-infrared (near-IR, 750–1400 nm) spectra but is lower in the IR part of the solar spectrum (Warren, 1982; Gardner and Sharp, 2010). The solar zenith angle (SZA; valid for direct radiation) and Published by Copernicus Publications on behalf of the European Geosciences Union
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