Preprints
https://doi.org/10.5194/tc-2022-260
https://doi.org/10.5194/tc-2022-260
 
20 Jan 2023
20 Jan 2023
Status: this preprint is currently under review for the journal TC.

On the importance of the humidity flux for the surface mass balance in the accumulation zone of the Greenland Ice Sheet

Laura Dietrich1, Hans Christian Steen-Larsen1, Sonja Wahl1,3, Anne-Katrine Faber1, and Xavier Fettweis2 Laura Dietrich et al.
  • 1Geophysical Institute, University of Bergen, and Bjerknes Center for Climate Research, Norway
  • 2University of Liège, Belgium
  • 3School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Switzerland

Abstract. It is highly uncertain how the humidity flux between the snow surface and the atmosphere contributes to the surface mass balance (SMB) of the interior Greenland Ice Sheet (GrIS). Due to sparse observations, evaluations of the simulated humidity flux are limited. Model-based estimates of the humidity flux contribution to the SMB are, therefore, unconstrained and even disagree in magnitude and sign. In this study, we evaluate the regional climate model MAR at the EGRIP (East Greenland Ice-Core Project) site in the accumulation zone of the GrIS. We use a combined dataset of continuous one-level bulk estimates of the humidity flux covering the period 05/2016–08/2019 and direct eddy-covariance humidity flux measurements from all four summer seasons. In summer, we document a bias of too little sublimation (-1.3 W m−2) caused by a cold bias in both air and surface temperature leading to a reduced humidity gradient. In winter, MAR overestimates deposition by about one order of magnitude. This is a consequence of an overestimated temperature gradient in too stable atmospheric conditions compared to observations. Both systematic errors cause a large discrepancy in the annual net humidity flux between the model and observations of -9 mm w. eq. yr−1. Remarkably, the simulated net annual humidity flux contributes positively to the SMB, contrary to observations documenting a net sublimation flux. We correct the systematic errors by applying a simple but effective correction function to the simulated latent heat flux. Using this correction, we find that 5.1 % of the annual mass gain at the EGRIP site sublimates again, and 4.3 % of the total mass gain is deposited vapor from the near-surface air. The estimated net humidity flux contribution to the annual SMB is about -1 % (net sublimation) compared to +5.6 % for the uncorrected simulation. In summer, the corrected MAR simulation shows that deposition accounts for 9.6 % of the total mass gain and that 31 % of the total mass gain at the EGRIP site sublimates again. The net fluxes contribute to -32 % of the summer SMB. These results demonstrate that the humidity flux is a major driver of the summer SMB in the accumulation zone of the GrIS and highlight that even small changes could increase its importance for the annual SMB in a warming climate.

Laura Dietrich et al.

Status: open (until 17 Mar 2023)

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Laura Dietrich et al.

Data sets

2m processed sensible and latent heat flux, friction velocity and stability at EastGRIP site on Greenland Ice Sheet, summer 2019. Steen-Larsen, Hans Christian; Wahl, Sonja https://doi.org/10.1594/PANGAEA.928827

Processed sensible and latent heat flux, friction velocity and stability at EastGRIP site on Greenland Ice Sheet. Steen-Larsen, Hans Christian; Wahl, Sonja; Box, Jason E; Hubbard, Alun L https://doi.org/10.1594/PANGAEA.946741

Laura Dietrich et al.

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Short summary
The contribution of the humidity flux to the surface mass balance in the accumulation zone of the Greenland Ice Sheet is uncertain. Here we evaluate the regional climate model MAR using a multi-annual dataset of eddy covariance measurements and bulk estimates of the humidity flux. The humidity flux largely contributes to the summer surface mass balance in the accumulation zone. In a warming climate, its importance for the annual SMB might increase.