A study of the energy balance and melt regime on Juncal Norte Glacier, semi-arid Andes of central Chile, using melt models of different complexity

Abstract

We use meteorological data from two automatic weather stations (AWS) on Juncal Norte Glacier, central Chile, to investigate the glacier–climate interaction and to test ablation models of different complexity. The semi-arid Central Andes are characterized by dry summers, with precipitation close to zero, low relative humidity and intense solar radiation. We show that katabatic forcing is dominant both on the glacier tongue and in the fore field, and that low humidity and absence of clouds cause strong radiative cooling of the glacier surface. Surface albedo is basically constant for snow and ice, because of the scarcity of solid precipitation. The energy balance of the glacier is simulated for a 2-month period in austral summer using two models of different complexity, which differ in the inclusion of the heat conduction flux into the snowpack and in the parameterization of the incoming longwave radiation. Net shortwave radiation is the dominant component of the energy balance. The sensible heat flux is always positive, while both the net longwave radiation and latent heat flux are negative. Neglecting the subsurface heat flux and corresponding variations in surface temperature leads to an overestimation of ablation of 2% over a total of 3695 mm water equivalent (w.e.) at the end of the season. Correct modelling of incoming longwave radiation is crucial, and we suggest that parameterizations based on vapour pressure and air temperature should be used rather than on computed cloud amount. We also used an enhanced temperature-index model incorporating the shortwave radiation flux, which has two empirical parameters. We apply it both with values of parameters obtained for Alpine glaciers and recalibrated on Juncal Norte. The model recalibrated against the correct energy balance simulations performs very well. The model parameters respond to the meteorological conditions typical of this climatic setting. Copyright © 2008 John Wiley & Sons, Ltd.