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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2018-154
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2018-154
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Sep 2018

Submitted as: research article | 04 Sep 2018

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This discussion paper is a preprint. It has been under review for the journal The Cryosphere (TC). A final paper in TC is not foreseen.

Evaluation of dynamically downscaled near-surface mass and energy fluxes for three mountain glaciers, British Columbia, Canada

Mekdes Ayalew Tessema1, Valentina Radić1, Brian Menounos2, and Noel Fitzpatrick1 Mekdes Ayalew Tessema et al.
  • 1Earth Ocean and Atmospheric Sciences Department (EOAS), The University of British Columbia, Vancouver, Canada
  • 2Natural Resources and Environmental Studies Institute and Geography Program, University of Northern British Columbia, Prince George, Canada

Abstract. Most models of glacier melt are forced by observed meteorological data in the vicinity of the glacier in question. In the absence of these observations, the forcing is commonly derived from statistical or dynamical downscaling of low resolution reanalysis datasets. Here we perform dynamical downscaling via the Weather Research and Forecasting (WRF) model in order to evaluate its performance against the observations from automatic weather stations (AWSs ) for three mountain glaciers in the interior of British Columbia, Canada over several summer seasons. The WRF model, nested within the ERA-Interim global reanalysis, produced output fields at 7.5 km and 2.5 km spatial resolution for all glaciers, as well as 1 km resolution for one of the glaciers. We find that the surface energy balance (SEB) model, forced by WRF at 2.5 km, adequately simulates the AWS-derived seasonal melt rates despite large biases in the individual SEB components. Overestimation of the number of clear sky days in WRF at 2.5 km explains the positive bias in the seasonal incoming shortwave radiation. This positive bias, however, is compensated by a negative bias in the seasonal incoming longwave radiation, and by an underestimation of sensible and latent heat fluxes. The underestimation of sensible heat fluxes down to −80 % of AWS-derived fluxes, as calculated by the bulk aerodynamic method, is due to the underestimated near-surface wind speeds. An increase of WRF spatial resolution from 7.5 to 1 km does not improve the simulation of downscaled variables other than near-surface air temperature. For relatively small glaciers (< 7 km length along the flowline), the grid spacing of ≥ 1 km is not fine enough to simulate the local cloud convection and topographic wind effects (katabatics). Since the incoming radiative fluxes, as dominant drivers of seasonal melting, are relatively well simulated (within 10 % difference from observed fluxes) by ERA-Interim at 80 km spatial resolution, there is no need for further downscaling of these radiative fluxes. Temperature and precipitation downscaling remains an important step for the simulation of turbulent fluxes and surface albedo.

Mekdes Ayalew Tessema et al.
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Mekdes Ayalew Tessema et al.
Mekdes Ayalew Tessema et al.
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Short summary
To force physics-based models of glacier melt, meteorological variables and energy fluxes are needed at or in vicinity of the glaciers in question. In the absence of observations detailing these variables, the required forcing is commonly derived by downscaling the coarse-resolution output from global climate models (GCMs). This study investigates how the downscaled fields from GCMs can successfully resolve the local processes driving surface melting at three glaciers in British Columbia.
To force physics-based models of glacier melt, meteorological variables and energy fluxes are...
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