Radiative and turbulent surface heat fluxes over sea ice in the western Weddell Sea in early summer

Abstract

[1] The radiative and turbulent heat fluxes between the snow-covered sea ice and the atmosphere were analyzed on the basis of observations during the Ice Station Polarstern (ISPOL) in the western Weddell Sea from 28 November 2004 to 2 January 2005. The net heat flux to the snowpack was 3 ± 2 W m À2 (mean ± standard deviation; defined positive toward snow), consisting of the net shortwave radiation (52 ± 8 W m À2 ), net longwave radiation (À29 ± 4 W m À2 ), latent heat flux (À14 ± 5 W m À2 ), and sensible heat flux (À6 ± 5 W m À2 ). The snowpack receives heat at daytime while releases heat every night. Snow thinning was due to approximately equal contributions of the increase of snow density, melt, and evaporation. The surface albedo only decreased from 0.9 to 0.8. During a case of cold air advection, the sensible heat flux was even below À50 W m À2 . At night, the snow surface temperature was strongly controlled by the incoming longwave radiation. The diurnal cycle in the downward solar radiation drove diurnal cycles in 14 other variables. Comparisons against observations from the Arctic sea ice in summer indicated that at ISPOL the air was colder, surface albedo was higher, and a larger portion of the absorbed solar radiation was returned to the atmosphere via turbulent heat fluxes. The limited melt allowed larger diurnal cycles. Due to regional differences in atmospheric circulation and ice conditions, the ISPOL results cannot be fully generalized for the entire Antarctic sea ice zone.

Albedo of coastal landfast sea ice in Prydz Bay, Antarctica: Observations and parameterization

“…Possible reasons contributing to the difference include the fact that our observations were based on the 1200 LST value when the solar zenith angle was near its daily minimum (the albedo was also near its daily minimum), while the observation time of Brandt et al (2005) was random. A 0.15 inter-diurnal variation was shown in our observations, and Vihma et al (2009) also observed a similar variation (0.14); the difference of 0.08 is among the range of inter-diurnal variation. Our values were based on direct measurements on the ice surface, while Brandt et al (2005) used ship-born sensors.…”

“…We calculated snow/bare-ice surface temperature from the downward/upward longwave fluxes with a fixed emissivity following the method of Pirazzini et al (2006). Because albedo measurements are not reliable under large solar zenith angles (Vihma et al, 2009), the albedo was calculated from the ratio Sw in /Sw out for zenith angles lower than 80 • , which is consistent with Pirazzini (2004) and Järvinen and Leppäranta (2013).…”

“…To understand and model the variability of Antarctic sea ice cover, accurate knowledge and parameterization of the albedo are needed. To date, most in-situ studies of solar radiation in polar seas have been carried out in the Arctic (e.g., Perovich et al, 2002;Perovich and Polashenski, 2012), while very limited observations of radiative characteristics and optical properties (especially albedo) have been performed over Antarctic sea ice (e.g., Allison et al, 1993;Brandt et al, 2005;Vihma et al, 2009;Weiss et al, 2012). Moreover, all the existing observational records over Antarctic sea ice are too short and do not cover the seasonal evolution and interannual variability, and sea-ice conditions around Antarctica differ significantly from those in the Arctic (Wendler et al, 2000).…”

A modern concept for autonomous and continuous measurements of spectral albedo and transmittance of sea ice

“…Frolov et al, 2005;Grenfell and Perovich, 2004;Perovich et al, 2002b) and Antarctic Cold Regions Science and Technology 62 (2010) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] (e.g. Allison et al, 1993;Brandt et al, 2005;Vihma et al, 2009). They were mostly based on transects during ship expeditions or on manual, discontinuous observations during ice (drift) stations.…”

Spatial and temporal variability in summer snow pack in Dronning Maud Land, Antarctica

“…Although melting occurred at the measurement site close to Basen, it was so limited that it did not have detectable effects on the diurnal cycle. This was also the case for the diurnal cycle of snow surface temperature during the Ice Station Polarstern in the western Weddell Sea in December 2004 (Vihma et al, 2009). The temperature profiles in the uppermost 0.30 m strongly depended on the cloud conditions, which controlled the downward radiative fluxes with opposite effects on solar shortwave and thermal longwave radiation.…”