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The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2017-14
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
24 Feb 2017
Review status
A revision of this discussion paper was accepted for the journal The Cryosphere (TC) and is expected to appear here in due course.
The importance of accurate glacier albedo for estimates of surface mass balance on Vatnajökull: Evaluating the surface energy budget in a Regional Climate Model with automatic weather station observations
Louise Steffensen Schmidt1, Guðfinna Aðalgeirsdóttir1, Sverrir Guðmundsson1,2, Peter L. Langen3, Finnur Pálsson1, Ruth Mottram3, Simon Gascoin4, and Helgi Björnsson1 1University of Iceland, Institute of Earth Sciences, Reykjavik, Iceland
2Keilir Institute of Technology, Reykjanesbær, Iceland
3Danish Meteorological Institute, Copenhagen, Denmark
4Centre d’Etudes Spatiales de la Biosphère, Université de Toulouse, CNES/CNRS/IRD/UPS, Toulouse, France
Abstract. A simulation of the surface climate of Vatnajökull ice cap, Iceland, made with the Regional Climate Model HIRHAM5 for the period 1980–2014, is used to estimate the evolution of the glacier mass balance. A new snow albedo parametrization is used for the simulation that describes the albedo with an exponential decay with time and is surface temperature dependant. The albedo scheme utilizes a new background map of the ice albedo created from observed MODIS data. The simulation is evaluated against observed daily values of weather parameters from five Automatic Weather Stations (AWSs) from 2001–2014, as well as in situ mass balance measurements from 1994–2014. The model simulates the observed parameters well at the station sites, albeit with a general underestimation of the net radiation. This is due to an underestimation of the incoming radiation and a general overestimation of the albedo. The average modelled albedo is overestimated in the ablation zone, which we attribute to an overestimation of the thickness of the snow layer and not taking dirt and volcanic ash deposition during dust storms and volcanic eruptions into account. A comparison with the specific summer, winter, and net mass balance for all of Vatnajökull from 1994–2014 shows a good overall fit during the summer, with the model underestimating the balance by only 0.04 m w.eq. on average, but a too large winter balance due to an overestimation of the precipitation at the highest areas of the ice cap. The average overestimation of the winter balance is 0.5 m w.eq., but a simple correction of the accumulation at the highest points of the glacier reduces this to 0.15 m w.eq. The model captures the evolution of the specific mass balance well, for example capturing a shift in the balance in the mid-1990s, which gives us confidence in the results for the entire model run. The model is therefore used to provide an estimate of the evolution of the specific surface mass balance of Vatnajökull from 1981, and we show the importance of bare glacier ice albedo to modelled mass balance and that processes not currently accounted for in RCMs, such as dust storms, are an important source of uncertainty in estimates of snow melt rate.

Citation: Schmidt, L. S., Aðalgeirsdóttir, G., Guðmundsson, S., Langen, P. L., Pálsson, F., Mottram, R., Gascoin, S., and Björnsson, H.: The importance of accurate glacier albedo for estimates of surface mass balance on Vatnajökull: Evaluating the surface energy budget in a Regional Climate Model with automatic weather station observations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-14, in review, 2017.
Louise Steffensen Schmidt et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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RC1: 'Referee review', Anonymous Referee #1, 28 Mar 2017 Printer-friendly Version Supplement 
AC1: 'Response to Referee #1', Louise Steffensen Schmidt, 24 May 2017 Printer-friendly Version Supplement 
 
RC2: 'Review of Schmidt et al.', Anonymous Referee #2, 26 Apr 2017 Printer-friendly Version Supplement 
AC2: 'Response to Referee #2', Louise Steffensen Schmidt, 24 May 2017 Printer-friendly Version Supplement 
Louise Steffensen Schmidt et al.
Louise Steffensen Schmidt et al.

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Short summary
The Regional Climate Model HIRHAM5 is evaluated over Vatnajökull, Iceland, using automatic weather stations and mass balance observations from 1995–2014. From this we asses whether the model can be used to reconstruct the mass balance of the glacier. We find that the simulated energy balance is underestimated overall, but it has been improved by using a new albedo scheme. The specific mass balance is reconstructed back to 1980, thus expanding on the observational records of the mass balance.
The Regional Climate Model HIRHAM5 is evaluated over Vatnajökull, Iceland, using automatic...
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