One-year measurements of surface heat budget on the ablation zone of Antizana Glacier 15, Ecuadorian Andes

Meteorological variables were recorded (14 March 2002 to 14 March 2003) at 4890 m above sea level (asl) on the Antizana Glacier 15 (0.71 km(2); 0degrees28'S, 78degrees09'W) in the tropical Andes of Ecuador (inner tropics). These variables were used to compute the annual cycle of the local surface energy balance (SEB). The four radiative fluxes were directly measured, and the turbulent fluxes were calculated using the bulk aerodynamic approach, calibrating the roughness length by direct sublimation measurements. The meteorological conditions are relatively homogeneous throughout the year (air temperature and air humidity). There is a slight seasonality in precipitation with a more humid period between February and June. During June-September, wind velocity shows high values and is responsible for intense turbulent fluxes that cause reduction of melting. Considering the SEB over the whole year, it is dominated by net radiation, and albedo variations govern melting. During the period under consideration the net short-wave radiation S (123 W m(-2)) and the sensible turbulent heat flux H (21 W m(-2)) were energy sources at the glacier surface, whereas the net long-wave radiation L (-39 W m(-2)) and the latent turbulent heat flux LE ( -27 W m(-2)) represented heat sinks. Since the OdegreesC isotherm-glacier intersection always oscillates through the ablation zone and considering that the phase of precipitation depends on temperature, temperature indirectly controls the albedo values and thus the melting rates. This control is of major interest in understanding glacier response to climate change in the Ecuadorian Andes, which is related to global warming and ENSO variability.