Near-surface climate and surface energy budget of Larsen C ice shelf, Antarctic Peninsula

Abstract

Abstract. Data collected by two automatic weather stations (AWS) on the Larsen C ice shelf, Antarctica, between 22 January 2009 and 1 February 2011 are analyzed and used as input for a model that computes the surface energy budget (SEB), which includes melt energy. The two AWSs are separated by about 70 km in the north-south direction, and both the near-surface meteorology and the SEB show similarities, although small differences in all components (most notably the melt flux) can be seen. The impact of subsurface absorption of shortwave radiation on melt and snow temperature is significant, and discussed. In winter, longwave cooling of the surface is entirely compensated by a downward turbulent transport of sensible heat. In summer, the positive net radiative flux is compensated by melt, and quite frequently by upward turbulent diffusion of heat and moisture, leading to sublimation and weak convection over the ice shelf. The month of November 2010 is highlighted, when strong westerly flow over the Antarctic Peninsula led to a dry and warm föhn wind over the ice shelf, resulting in warm and sunny conditions. Under these conditions the increase in shortwave and sensible heat fluxes is larger than the decrease of net longwave and latent heat fluxes, providing energy for significant melt.

Surface energy budget on Larsen and Wilkins ice shelves in the Antarctic Peninsula: results based on reanalyses in 1989–2010

“…2). The value on LCIS compares well with that of about 20 cm (8.7 Wm −2 ) measured by Kuipers Munneke et al (2012Munneke et al ( ) in 2009Munneke et al ( -2011. For WIS we obtained 36-73 melt days per summer and the melt varied from 10 to 23 cm w.e.…”

“…The warm-air advection together with large downward longwave radiation under extensive cloud cover contributed to the high air and snow surface temperatures on LCIS. Also, previous studies have indicated that high temperatures on Larsen Ice Shelf were found together with north-westerly winds (Kuipers Munneke et al, 2012) and the breakup of Larsen B Ice Shelf in 2002 was preceded by northwesterly winds (van den Broeke, 2005). During the winter with anomalously small surface net energy flux, the mean sea level pressure was higher than during the winters when the surface net flux was close to the long term average.…”

“…We note that neither we nor van den Broeke (2005) took into account the absorption of solar radiation into the snow. The penetration of shortwave radiation into the snow changes the partitioning between surface and subsurface melt, and increases the total melt (Cheng et al, 2008;Kuipers Munneke et al, 2012).…”

“…A recent study by Kuipers Munneke et al (2012) addresses the weather conditions on Larsen C Ice Shelf (LCIS, Fig. 1) and their effect on the ice shelf's surface net flux.…”

“…In conditions of a warm snowpack, the penetration of solar radiation increases subsurface melting and decreased surface melting, the former being dominant, thus leading to a larger net melt. Kuipers Munneke et al (2012) also draw attention to the connection between westerly winds and weather conditions on LCIS. Moderate or strong westerly flow over the peninsula leads to northerly flow on the east side of the peninsula (Orr et al, 2004), together with föhn winds, cloudless skies and advection of warm and dry air on the eastern side of the peninsula (Marshall et al, 2006;van Lipzig et al, 2008).…”