The physical, radiative and microwave scattering characteristics of melt ponds on Arctic landfast sea ice

Melt ponds are an important characteristic of Arctic sea ice because of the ir control on the surface radiation balance. Little is known about the phys ical nature of these features and to date there is no operational method fo r detection of their formation or estimation of their aerial fraction. Coin cident in situ observations, aerial surveys and synthetic aperture radar da ta from a field site in Arctic Canada are compared in an evaluation of the physical, radiative and electrical properties of melt ponds on first-year a nd multiyear sea ice. Results show that the interrelationships between the thermal diffusivity and conductivity of the snow cover control the mechanis ms of snow ablation. Aerial fractions of snow patches, and light and dark c oloured melt ponds, show considerable variation both as a function of proxi mity to land and due to ice type. First-year sea ice is shown to have a wat er background with discrete snow patches distributed throughout. Multiyear sea ice consists of discrete 'particles' within a snow background. Morpholo gical measurements indicate that snow patches range in size with average ar eas of from 5 to 20 m(2). Pond sizes over multiyear sea ice are also highly variable with averages ranging from 15 to 20 m(2). The integrated shortwav e albedo was measured in the field and averaged to: snow patches (0.64+/-0. 07); light melt ponds (0.29 +/- 0.04); and dark melt ponds (0.14 +/- 0.03). Snow patch size statistics explained a statistically significant proportio n of the surface shortwave albedo. We found that microwave scattering could be used to obtain a measure of the onset of melt and had utility in detect ing subtle details of the thermodynamic transition from winter through earl y melt into pond formation. We formalized a statistical relationship betwee n microwave scattering and surface climatological albedo (sigma degrees-alp ha relationship). We found the relationship valid only for landfast first-y ear sea ice under windy conditions. We conclude with a discussion of the ro le of surface wind stress and diurnal cycling in specification of the sigma degrees-alpha relationship.