The objective of this study is to evaluate the surface energy balance (SEB) of a cold, high-altitude tropical glacier, Illimani (16d39'S; 67d47'W, 6340 m above sea level), where a 137 m ice core was drilled down to the bedrock in June 1999. During the dry austral winter, tropical glaciers are known to experience strong sublimation, which may be responsible for snow composition changes through postdepositional processes. In order to help toward the interpretation of this climatic archive, SEB experiments were carried out in 1999, 2001, and 2002, during the dry season (mostly clear and cold atmosphere, strong westerly winds).
The daily net all-wave radiation is usually negative during this austral dry winter because of the highly reflective snow surface and because of reduced incoming longwave radiation due to a low cloudiness compared to outgoing long-wave radiation. The turbulent heat fluxes were evaluated using the bulk aerodynamic approach, including stability correction. The roughness parameters are deduced from direct sublimation measurements and serve as calibration parameters. The sensible heat flux strongly heats the surface at night but changes to negative values during daytime unstable conditions (between 1000 and 1600 LT). The latent heat flux is always negative, which means that the surface loses mass through sublimation, particularly in the daytime (sublimation rates are -1.2 mm w.e./d, -0.7 mm w.e./d, and -0.8 mm w.e./d during the 2001, 2002, and 1999 measuring periods, respectively, where w.e. is water equivalent).
The winter SEB of this high-altitude cold tropical glacier is comparable to the summer SEB over snow surfaces of the intermediate slopes of Antarctica.