Using 3D turbulence-resolving simulations to understand the impact of surface properties on the energy balance of a debris-covered glacier
Abstract. Debris-covered glaciers account for 18 % of the total glacier ice volume in High Mountain Asia, however the drivers controlling the melt of these glaciers are still largely unknown and their total contribution to the total glacier melt remains uncertain. Debris influences the surface energy balance and therefore glacier melt by influencing the thermal properties (e.g. albedo, thermal conductivity, roughness) of the glacier surface. In this study, the impact of surface properties of debris on the spatial distribution of micro meteorological variables, such as the turbulent fluxes, wind fields, moisture and temperature and eventually the conductive heat flux for a debris-covered glacier is investigated. We simulated a debris-covered glacier (Lirung Glacier, Nepal) at a high-resolution of 1 m with the MicroHH model with boundary conditions retrieved from an automatic weather station (temperature, wind and specific humidity) and UAV flights (digital elevation map and surface temperature), and the model is validated with eddy covariance data. Subsequently, a sensitivity analysis was performed to ascertain how heterogeneous surface variables control the glacier micro-climate. Additionally, we show ice cliffs are local melt hot spots and that turbulent fluxes and local heat advection amplify spatial heterogeneity on the surface. The high spatial variability of small-scale meteorological variables suggests that point based station observations cannot be simply extrapolated to an entire glacier and should be considered in future studies for a better estimation of glacier melt in High Mountain Asia.
