On the use of radiosondes to model glacier ablation

Abstract

Data from twice-daily radiosonde flights are used to estimate spatial and temporal variations of air temperature, atmospheric transmissivity, wind speed and humidity at Blue Glacier, western Washington. U. S.A. Results indicate that the free-air conditions (interpolated in altitude and in time from radiosondes) provide a much better estimate of conditions on the glacier than do measurements from low-altitude stations. Data from the radiosondes are used to model the hourly exchange of mass and energy at the surface of Blue Glacier. In the absence of explicit information about clouds, temperature and humidity profiles from the radiosonde are used to estimate the atmospheric transmissivity needed for the calculation of short-wave radiation. Topographical influences (altitude, shading, slope angle and orientation) and surface albedo are parameterized explicitly to model the absorbed solar flux at specific sites on the glacier, Other energy fluxes (long-wave radiation, sensible-heat and latent-heat exchange) are estimated using established physical models. Hourly estimates of ablation are integrated to obtain the seasonal ablation. Modeled ablation and stake measurements made over 30 a at two sites on Blue Glacier agree within 16%, which is within the error associated with stake measurements of ablation.