Papers Online - #156

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

by
  • Joseph Sheedy and Gerd Wendler
    Geophysical Institute
    University of Alaska, Fairbanks
    Alaska, USA

    and

    Anthony Worby
    Antarctic CRC and Australian Antarctic Division
    PO Box 252-80
    Hobart, Tasmania, 7001, AUSTRALIA

    Abstract

    The surface radiation budget was continuously measured in the sea ice zone between 140°E (Adélie Land) 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 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 hours for the majority of the cruise. Due to a high amount of fractional cloudiness, the global radiation was somewhat reduced when compared to areas with less cloud amount. 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. if it is covered with snow, flooded, melting or dry. Detailed ice observations were carried out. Hourly values of the albedo varied from 8% (open water) to 77% (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 long wave incoming radiation from the atmosphere. A mean value of -40 W m-2 was measured, displaying only a very weak diurnal course. The sum of the short and long wave radiation, the total radiation budget, showed the expected diurnal variation, with slightly negative values at night (for 6 hours), and a mean maximum at solar noon of around 220 W m-2. A mean daily value of 98 W m-2 was calculated.

     

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    Gerd Wendler
    gerd@gi.alaska.edu
    Date Last Modified: 4/30/00