Sublimation on the glaciers of the upper Huasco valley, Chile, using eddy covariance data and energy balance modelling

Christophe Kinnard

The paper tries to reconcile the facts that there are often useful correlations between ablation or run-off and air temperature while net radiation is usually the major source of ablation energy. Equations are derived from the energy balance to describe statistics for the ablation-temperature relation in terms of statistics for the relations between individual energy fluxes and air temperature. As examples, statistics are evaluated for four published series from Arctic Canada. Although the net radiation is the largest energy source in all four cases, the ablation rate is moderately well correlated with temperature and poorly correlated with net radiation. This is because the sensible heat flux is more variable than the radiation in three cases and is itself better correlated with temperature in all four cases. The major contributions to the increase of ablation rate with temperature (on average 6.3 kg m−2 d−1 deg−1) are due to sensible heat, followed by latent heat with a small cont...

Two models that estimate glacier ablation from simple meteorological observations are described. Both the energy-balance and bulk-aerodynamic approaches are used to determine the bulk-exchange coefficient for transfer of sensible- and latent-heat energy to the melting ice surface from 17 summer days of measurement on Ivory Glacier, New Zealand. The behaviour of the coefficient is examined over progressively increasing time intervals and as a function of wind speed and gradient, and of atmospheric stability. The models are verified with 36 d of independent data from a different summer on the same glacier. The more accurate short-term estimates of ablation are obtained using the energy-balance approach with empirically but independently derived values of the exchange coefficient.

We report on analysis of meteorological data for the period 27 May–20 August 2004, from two automatic weather stations on McCall Glacier, Alaska, USA, aimed at studying the relationship between climate and ablation. One station is located on a mountain ridge and the other in the ablation area where we also analyzed the energy balance. The weather station on the glacier measured an average temperature of 5.3°C (at 2 m height above surface) and wind speed of 3.1 m s−1 (at 3 m height). A sonic height ranger and ablation stakes indicate a specific mass balance of –1.94 ± 0.09 m w.e between 15 June and 20 August. The specific mass balance calculated from the surface energy balance, –2.06 ± 0.18 m w.e., is in close correspondence to this. The latter is the sum of 0.12 m w.e. of snowfall, 0.003 m w.e. of deposition and –2.18 m w.e. of melt. Net radiation contributes 74% of the melt energy. Compared to ablation measurements in the early 1970s, summer ablation was large. This increase is exp...

Geophysical Research Abstracts Vol. 12, EGU2010-11006, 2010 EGU General Assembly 2010 © Author(s) 2010 Sublimation on the glaciers of the upper Huasco valley, Chile, using eddy covariance data and energy balance modelling Shelley MacDonell (1), Nicolas Cullen (2), Lindsey Nicholson (3), Thomas Mölg (3), and Christophe Kinnard (1) (1) Centro de Estudios Avanzados en Zonas Aridas (CEAZA), Glaciology, La Serena, Chile (shelley.macdonell@gmail.com), (2) Department of Geography, University of Otago, Dunedin, New Zealand, (3) Tropical Glaciology Group, Department of Earth and Atmospheric Sciences, University of Innsbruck, Innsbruck, Austria On the cold, arid glaciers of the Norte Chico region, Chile, sublimation plays an important role in mass loss from the glacier surface. The ratio of sublimation : melt on these glaciers dictates not only the amount of meltwater delivered to the watershed, but it also drives the development of morphological features on the glacier surface, such as penitentes. As the rate of sublimation is driven by the latent heat flux, understanding the behaviour of the turbulent heat flux across the glacier surface is key to quantifying the spatial and temporal patterns of ablation. We measured the turbulent heat fluxes at a point on the surface of the Guanaco Glacier during 23-31 January, 2008 using an open-path eddy covariance system. The eddy covariance system was installed adjacent to an existing automatic weather station operating at 5325 m on the glacier surface, in a region devoid of penitents and other surface deformities. The results from the eddy covariance measurements were subsequently used to assess the sublimation results calculated using a point energy balance model. Results showed that 0.5-3 mm w.e. of sublimation occurred per day during the study period, which corresponded well with the energy balance results. However to assess the total sublimation rate on this glacier, sublimation rates from penitentes, ablation cusps and debris-covered regions must also be calculated. Thus this paper will also take a first look at another set of eddy covariance measurements made in a penitente field on the Toro 1 Glacier between December 2009-January 2010 to quantify the importance of penitentes for producing ablation on these glaciers as well. The eddy covariance system was installed adjacent to an existing automatic weather station operating at 5200 m on the glacier surface, in a location with a 100 m fetch of penitentes. From these measurements we are able to ascertain the role that penitentes play in modifying turbulent heat fluxes in the main part of the ablation season, the results of which were compared to results from a point energy balance model. In future, these results will also be used to validate a distributed energy balance model for this glacier.

RELATED PAPERS

RELATED TOPICS

Log In

Sublimation on the glaciers of the upper Huasco valley, Chile, using eddy covariance data and energy balance modelling

Sublimation on the glaciers of the upper Huasco valley, Chile, using eddy covariance data and energy balance modelling

Related Papers

RELATED PAPERS

RELATED TOPICS