Effects of local advection on the spatial sensible heat flux variation on a mountain glacier
Abstract. Distributed mass balance models, which translate micrometeorological conditions into local melt rates, have proven deficient to reflect the energy flux variability on mountain glaciers. This deficiency is predominantly related to shortcomings in the representation of local processes in the forcing data. We found by means of idealized Large-Eddy Simulations that heat advection, associated with local wind systems, cause small-scale heat flux variations by up to 100 Wm−2 during clear sky conditions. Here we show that process understanding at a few on-glacier sites is insufficient to infer on the wind and temperature distributions across the glacier. On average, glacier heat fluxes are both over- and underestimated by up to 16 Wm−2 when using extrapolated temperature and wind fields. The sign and magnitude of the errors depend on the site selection as well as on the flow direction. Our results demonstrate how the shortcomings in the local heat flux estimates are related to topographic effects and the insufficient characterisation of the temperature advection process. The magnitudes of the surface heat flux errors are strong enough to significantly affect the surface energy balance and derived climate sensitivities of mountain glaciers.