Snow albedo sensitivity to macroscopic surface roughness using a new ray-tracing model

• Published in: The cryosphere Vol. 14; no. 5; pp. 1651 - 1672
• Main Authors: Larue, Fanny, Picard, Ghislain, Arnaud, Laurent, Ollivier, Inès, Delcourt, Clément, Lamare, Maxim, Tuzet, François, Revuelto, Jesus, Dumont, Marie
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 27.05.2020; Copernicus; Copernicus Publications
• Subjects: Albedo; Albedo (solar); Analysis; Broadband; Budgets; Computer simulation; Energy (Physics); Energy budget; Incidence angle; Monte Carlo methods; Monte Carlo simulation; Orientation; Other; Photons; Radiation; Radiation (Physics); Ray tracing; Sciences of the Universe; Sensitivity; Short wave radiation; Snow; Snowpack; Spectral albedo; Statistical methods; Sun; Surface energy; Surface properties; Surface roughness; Surface science; Alps
• ISSN: 1994-0424; 1994-0416; 1994-0424; 1994-0416
• DOI: 10.5194/tc-14-1651-2020

Most models simulating snow albedo assume a flat and smooth surface, neglecting surface roughness. However, the presence of macroscopic roughness leads to a systematic decrease in albedo due to two effects: (1) photons are trapped in concavities (multiple reflection effect) and (2) when the sun is low, the roughness sides facing the sun experience an overall decrease in the local incidence angle relative to a smooth surface, promoting higher absorption, whilst the other sides have weak contributions because of the increased incidence angle or because they are shadowed (called the effective-angle effect here). This paper aims to quantify the impact of surface roughness on albedo and to assess the respective role of these two effects, with (1) observations over varying amounts of surface roughness and (2) simulations using the new rough surface ray-tracing (RSRT) model, based on a Monte Carlo method for photon transport calculation.