The surface energy budget in the Antarctic summer sea-ice pack

Abstract

AbstractThe surface radiation budget was continuously measured in the sea-ice zone between 140° E (Terre Adélie) and 180° (McMurdo Sound) close to mid-summer, when the sea ice is disintegrating. These measurements were carried out during a cruise of the USCGC Polar Sea from Hobart, Tasmania, to McMurdo station, Antarctica, in 1998/99. Some of the findings are: the solar radiation is the major atmospheric energy source for the melting of ice. The sun was above the horizon for 24 h for most of the cruise. Due to a high amount of fractional cloudiness, the global radiation was somewhat reduced when compared to areas with lesser cloud cover Mean noon values were around 400 W m−2, while at midnight a value of 30 W m−2 was measured. Daily mean values of the net shortwave radiation varied widely, a function of the reflectivity of the surface, which is strongly dependent not only on the ice concentration, but also on the ice type (e.g. whether it is covered with snow, flooded, melting or dry). Detailed ice observations were carried out. Hourly values of the albedo varied from 6% (open water) to 84% (10/10 sea ice with a dry snow cover). The mean net longwave radiation was only modestly negative. The high amount of fractional cloud cover increased the longwave incoming radiation from the atmosphere. A mean value of −40 W m−2 was measured, which displayed only a very weak diurnal course. The sum of the short- and longwave radiation, the total radiation budget, showed the expected diurnal variation, with slightly negative values at night (for 6 h), and a mean maximum at solar noon of around 220 W m−2. A mean daily value of 98 W m−2 was calculated.