Energy Exchange on a Melting Glacier

Abstract

<p>Although methods of evaluating various energy exchanges between the atmosphere and the earth's surface are available, a need for additional knowledge about the turbulent transfer of sensible and latent heat on a melting glacier is recognized. The micrometeorological investigation described in this study is a response to this need. A measurement programme was conducted during the summer of 1971 on Peyto Glacier, Alberta. Data collected include net radiation, melt energy, and the atmospheric parameters, wind speed, temperature and vapour pressure, at several levels above the ice.</p> <p>Emphasis is placed upon computing sensible and latent heat exchange from profiles of the atmospheric parameters. This is approached through an examination of boundary layer thickness, stability relationships in the boundary layer, and surface roughness lengths. Since all temperature profiles showed inversions, the results characterize stable conditions, where turbulence is dampened. In addition, katabatic flow results from the slope of the glacier.</p> <p>Turbulent boundary layers in stable flow are known to be relatively thin, but an unexpectedly thin boundary layer, approximately one metre thick, is found over the glacier. The thinness of this layer is attributed to katabatic control of the flow. Deviation from the adiabatic profile form due to stability is adequately described by a log-linear framework, a finding which agrees with other work. However, is is accompanied by an inequality of transfer coefficients, that for heat exceeding that for momentum. This has not been reported previously. A tentative hypothesis is advanced to explain this. Contrary to previous glaciological opinion, the wind profile roughness length is found to be smaller than that of the temperature profile. This is explained using results of other work on other surfaces.</p> <p>A bulk transfer procedure is chosen as the most suitable method of evaluating the turbulent fluxes. The procedure is strengthened by the findings of this study. It is used to obtain half-hourly estimates of sensible and latent heat exchange which appear to be reasonable. Short-term variations in the meltwater, hydrograph are found to be closely controlled by the net radiative flux, but daily totals indicate that the sensible heat flux is also an important energy source. Latent heat transfer by the water vapour flux between the atmosphere and the surface is small.</p> <p>The contribution of this investigation to establishing the link between glacier hydrology and climate is indicated.</p>