Abstract
Abstract. Ice shelves in the Antarctic Peninsula have significantly disintegrated during recent decades. To better understand the atmospheric contribution in the process, we have analysed the inter-annual variations in radiative and turbulent surface fluxes and weather conditions over Larsen C Ice Shelf (LCIS) and Wilkins Ice Shelf (WIS) in the Antarctic Peninsula in 1989–2010. Three atmospheric reanalyses were applied: ERA-Interim by ECMWF, Climate Forecast System Reanalysis (CFSR) by NCEP, and JRA-25/JCDAS by the Japan Meteorological Agency. In addition, in situ observations from an automatic weather station (AWS) on LCIS were applied, mainly for validation of the reanalyses. The AWS observations on LCIS did not show any significant temperature trend, and the reanalyses showed warming trends only over WIS: ERA-Interim in winter (0.23 °C yr−1) and JRA-25/JCDAS in autumn (0.13 °C yr−1). In LCIS from December through August and in WIS from March through August, the variations of surface net flux were partly explained by the combined effects of atmospheric pressure, wind and cloud fraction. The explained variance was much higher in LCIS (up to 80%) than in WIS (26–27%). Summer melting on LCIS varied between 11 and 58 cm water equivalent (w.e.), which is comparable to previous results. The mean amount of melt days per summer on LCIS was 69. The high values of melting in summer 2001–2002 presented in previous studies on the basis of simple calculations were not supported by our study. Instead, our calculations based on ERA-Interim yielded strongest melting in summer 1992–1993 on both ice shelves. On WIS the summer melting ranged between 10 and 23 cm w.e., and the peak values coincided with the largest disintegrations of the ice shelf. The amount of melt on WIS may, however, be underestimated by ERA-Interim, as previously published satellite observations suggest that it suffers from a significant bias over WIS.
Highlights
Ice shelves, floating extensions of land ice, are found together with the glaciers and ice sheets with a marine terminus
Our study revealed significant differences between ERAI, Climate Forecast System Reanalysis (CFSR) and JRA on Larsen C Ice Shelf (LCIS) and Wilkins Ice Shelf (WIS)
Near-surface variables of reanalyses have not been previously validated over Antarctic Peninsula ice shelves, as previous validation studies of atmospheric reanalyses in the Antarctic have mostly focused on large-scale features, such as cyclones (Hodges et al, 2011) and precipitation (Bromwich et al, 2011)
Summary
Ice shelves, floating extensions of land ice, are found together with the glaciers and ice sheets with a marine terminus. The collapses of the ice shelves are believed to be partly caused by atmospheric warming (Rott et al, 1998; Scambos et al, 2000; Shepherd et al, 2003) and increased surface melting (van den Broeke, 2005). Van den Broeke (2005) mentions that the increase in warm-air advection and the strengthening of the föhn effect, caused by a perturbation in atmospheric circulation, have their share in the decrease in ice shelf area in the Antarctic Peninsula. 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. Our primary objective is to find out (1) how the net surface heat flux (sum of radiative and turbulent surface fluxes) varies inter-annually, (2) how the flux variations are related to large-scale weather conditions, (3) how much summer melt the net heat flux generates, and (4) how the summer melt varies inter-annually and compares with the observed disintegration events of the ice shelves
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