Influence of Melt Ponds and Floe Size on Apparent Optical Properties of Sea Ice: An Idealized Modelling Investigation

Melt ponds are usually modeled for light transfer as horizontally infinite water layers on level ice, and the albedo of floe is determined by a linear combination (LC) of melt pond and bare ice albedos weighted by their areal coverages. However, this method does not reflect the actual conditions because ice floes have a limited size. In the present study, an idealized two-dimensional Monte Carlo (MC) model was employed to investigate the influence of melt ponds and floe size on the apparent optical properties (AOPs) of summer sea ice. The results showed that the albedo and vertical light transmittance of large floes mainly depend on the melt pond fraction and ice thickness, which is consistent to previous results. However, also the floe size plays an important role in the AOPs of small floes. Two parameters were proposed to present the accuracy of the LC method for small floes with lower sea ice concentration: the ratios of sea ice albedo and transmittance determined by the LC (alpha T-line,(line)) to the values in the MC model (alpha, T), K-alpha = alpha(line)/alpha, and K-T = T-line/T, respectively. Due to the lateral transmittance, K-alpha, K-T >= 1 and asymptotically approach 1 with floe size increasing to infinity. To reduce the biases in albedo and transmittance due to floe size, new parameterization formulas were provided for K-alpha and K-T with the distance into the marginal ice zone and in different melting stages. The results have potential to be implemented into future sea ice models to correct the AOPs of small sea ice floes obtained via the LC method.