Melt and surface sublimation across a glacier in a dry environment: distributed energy-balance modelling of Juncal Norte Glacier, Chile

Previous estimates of melt and surface sublimation on glaciers of the subtropical semiarid Andes (29-34 degrees S) have been obtained at few specific locations, but it is not clear how ablation components vary across the entire extent of a glacier in this dry environment. Here, we simulate the distributed energy and mass balance of Juncal Norte Glacier (33 degrees S) during a 2-month summer period. Forcing fields of near-surface air temperature and wind speed are generated using two methods accounting for the main physical processes that shape their spatial variations. Simulated meteorological variables and ablation agree well with observations on the glacier tongue and reveal complex patterns of energy and mass fluxes. Ablation decreases from 70 mm w.e. d(-1) at the low-albedo glacier terminus (similar to 3000 m), where almost 100% of total ablation corresponds to melt, to <5 mm w.e. d(-1) at wind-exposed, strong-radiated sites above 5500 m, where surface sublimation represents > 75% of total ablation. Our simulations provide the first glacier-scale estimates of ablation components on a glacier in the study region and better reproduce the observed and expected spatial variations of melt and surface sublimation, in comparison with more simple assumptions, such as linear gradients and uniform wind speeds.