Assessing the role of sublimation in the dry snow zone of the Greenland ice sheet in a warming world

Abstract

Meteorological and glaciological data obtained over an intensive 2 year measurement period (2000)(2001)(2002) are used to run a physically based climatic mass balance model to characterize a seasonal variability in mass and energy exchanges at Summit, Greenland. The model resolves the full surface energy balance and the subsurface temperature profile by inclusion of energy release from penetrating shortwave radiation. A Monte Carlo approach using 1000 different parameter combinations is adopted to assess model uncertainty, with output compared to measured surface and subsurface temperatures, changes in surface height, and eddy correlation data. The heat exchanges associated with the change in phase of water are very small in all seasons, with the average turbulent latent heat flux equal to 0.4 (±0.2) W m À2 . This suggests that the mean annual water vapor gradient is toward the surface, resulting in a mass gain of 4.1 mm WE yr À1 . The mass gain represents only a small fraction of the total accumulation (<2%), in part because of the change in sign of the water vapor flux from winter (deposition) to summer (sublimation), but if assumed to be typical of the entire dry snow zone (40% of the total ice sheet area) is equivalent to approximately 5.5 Gt yr À1 . A simple experiment based on 2012 atmospheric conditions suggests that mass turnover from water vapor exchanges will likely be enhanced in a warming climate, with sublimation increasing more than deposition. Should the sign of the mean turbulent latent heat flux change due to warming, the present mass gain in the dry snow zone could easily become a mass loss of equal proportion, which would further enhance the negative mass balance of the Greenland ice sheet.

Numerical simulation of extreme snowmelt observed at the SIGMA-A site, northwest Greenland, during summer 2012

“…Averaged gradients between the surface and the lower measurement height during the IOP were 1.6 s −1 , 0.3 • C m −1 , and −0.15 hPa m −1 , respectively. The value for vapor pressure is very close to that obtained at Summit during 2000-2002 as reported by Cullen et al (2014). However, averaged gradients between the lower and upper measurement heights were nearly 0, except for the case of wind speed, for which it was 0.2 s −1 .…”

“…Comparison between OBS_2LM and OBS_1LM shows that the former obviously tends to be higher than the latter, and sometimes the signs of the fluxes are different. According to previous studies Cullen et al, 2014), the sign and magnitude of the latent heat fluxes from the 1LM and 2LM methods agree reasonably at low elevations on the GrIS, whereas they often differ from each other at the higher elevations. Measurements conducted previously in the northwest GrIS (the Humboldt and GITS sites) showed that the net annual sublimation from the 1LM and 2LM methods did not agree sufficiently at both sites ).…”

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

“…The model structure used in this study is explained in detail by Mölg et al (2012) with the latest model version (2.4) used by Mölg (2015). The model calculates the surface and near-subsurface mass and energy fluxes and has been successfully applied to address various questions in a range of climatic conditions (Collier et al, 2013;Conway and Cullen, 2015;Cullen et al, 2007Cullen et al, , 2014Gurgiser et al, 2013a, b;MacDonell et al, 2013;Mölg et al, 2014;Nicholson et al, 2013). The model computes the mass balance as the sum of solid precipitation, surface deposition, internal accumulation (refreezing of liquid water in snow), change in englacial liquid water storage, subsurface and surface melt, and sublimation.…”

Exploring the concept of maximum entropy production for the local atmosphere‐glacier system

“…The model of this linkage is described in detail in Mölg et al . [, 2012] and has been applied to various questions and climatic environments around the world [e.g., Conway and Cullen , ; Gurgiser et al ., ; MacDonell et al ., ; Nicholson et al ., ; Cullen et al ., ; Mölg et al ., ]. Therefore, only a brief model description is given here.…”