The Effect Of Snow At Forest Floor On Boreal Forest Albedo Diurnal And Seasonal Variation During The Melting Season

Seasonal snow cover affects markedly the albedo values of the boreal forest zone. It increases the forest albedo values and changes the diurnal variation of albedo compared to snow-free situations. Snow is also a high scatterer in visible and near-infrared wavelengths, and thus the probability of multiple scattering between forest floor and canopy is high. A photon recollision probability based model called PARAS, where multiple scattering components are included, was used to simulate albedo values of needleleaved evergreen forest with and without snow cover on the forest floor. We focused on two example dates representing typical premelt and melting season snow conditions in clear-sky cases, and multiple overcast days over melting season, and compared the diurnal and seasonal variations to estimate the effect of snow cover and multiple scattering. We found that changing the forest floor surface from snow-free to snow-covered changes the diurnal variation characteristics of the clear-sky albedo from U-shaped to W-shaped. In addition, ignoring the effect of the forest floor or multiple scattering leads to relative underestimation of forest albedo values and reflected solar energy, of up to 80% (up to 1.0 kWh/m(2)) and 30% (up to 0.25 kWh/m(2)), respectively. The underestimations depend on the forest floor cover type and the season.