Modelling ice and snow melt is of large practical and scientific interest, including issues such as water resource management, avalanche forecasting, glacier dynamics, hydrology and hydrochemistry, as well as the response of glaciers to climate change. During the last few decades, a large variety of melt models have been developed, ranging from simple temperature-index to sophisticated energy-balance models. There is a recent trend towards modelling with both high temporal and spatial resolution, the latter accomplished by fully distributed models. This review discusses the relevant processes at the surface-atmosphere interface, and their representation in melt models. Despite considerable advances in distributed melt modelling there is still a need to refine and develop models with high spatial and temporal resolution based on moderate input data requirements. While modelling of incoming radiation in mountain terrain is relatively accurate, modelling of turbulent fluxes and spatial and temporal variability in albedo constitute major uncertainties in current energy-balance melt models, and thus need further research.

http://weather.unbc.ca/wordpress/wp-content/uploads/2014/02/Hock_2005.pdf

Glacier melt: a review of processes and their modelling

Spatial and temporal variations in aerodynamic roughness length (z0) on Haut Glacier d'Arolla, Switzerland, during the 1993 and 1994 ablation seasons are described, based on measure- ments of surface microtopography. The validity of the microtopographic z0 measurements is established through comparison with independent vertical wind profile z0 measurements over melting snow, slush and ice. The z0 variations are explained through correlation and regression analyses, using independent measurements of meteorological and surface variables, and parameterizations are developed to calculate z0 variations for use in surface energy balance melt models. Several independent variables successfully explain snow z0 variation through their correlation with increasing surface roughness, caused by ablation hollow formation, during snow melt. Non-linear parameterizations based on either accumulated melt or accumulated daily maximum temperatures since the most recent snowfall explain over 80% of snow z0 variation. The z0 following a fresh snowfall on an ice surface is parameterized based on relationships with the underlying ice z0, snow depth and accumulated daily maximum temperatures. None of the independent variables were able to successfully explain ice z0 variation. Although further comparative studies are needed, the results lend strong support to the microtopo- graphic technique of measuring z0 over melting glacier surfaces.

http://arctic.eas.ualberta.ca/downloads/Brock%20et%20al%20J%20Glaciol%202006.pdf

Measurement and parameterization of aerodynamic roughness length variations at Haut Glacier d'Arolla, Switzerland

Numerical modelling of the energy balance and the englacial temperature of the Greenland Ice Sheet. Calculations for the ETH-Camp location (West Greenland, 1155 m a.s.l.)

The katabatic flow over glaciers is studied with data from automatic weather stations (AWS). Weanalyse data from the Morteratschgletscher (Switzerland), Vatnaj¨okull (Iceland) and West Greenland,and conclude that katabatic flow is very common over melting glacier surfaces and rarely disruptedby the large-scale flow. Over small and medium-size glaciers the height of the wind maximum isgenerally low (typically 10 m), and vertical temperature differences near the surface are very large(up to 15 K over 4 m). In glacier mass-balance models there is a great need for parameterisations ofthe surface heat flux. We develop a simple method to estimate the sensible heat flux F associatedwith the glacier wind. It is based on the classical Prandtl model for slope flows. We set the turbulentexchange coefficient proportional to the maximum wind speed (velocity scale) and the height of thewind maximum (length scale). The resulting theory shows that F increases quadratically with the temperaturedifference between the surface and the ambient atmosphere; F decreases with the square rootof the potential temperature gradient of the ambient atmosphere; and F is independent of the surfaceslope. DOI: 10.1034/j.1600-0870.2002.201398.x

Glacier winds and parameterisation of the related surface heat fluxes

Since 1 October 1995, an automatic weather station has been operated on
the tongue of Morteratschgletscher, Switzerland. The station stands freely on the ice, and
sinks with the melting glacier surface. It is located at 2100 m a.s.l., and measures air temperature,
wind speed and direction, incoming and reflected solar radiation, pressure and
snow temperature. A sonic ranger, mounted to stakes drilled into the ice, measures surface
height from which melt rates and snow accumulation can be derived. In this paper the
data for the period 1 October 1995 to 30 September 1998 are used to evaluate the surface
energy balance. The turbulent energy fluxes are calculated with the bulk method. The
turbulent exchange coefficient Ch is used as a control parameter. With Ch = 0.00127 the
calculated melt equals the observed melt, which is 17.70 m w.e. over the 3 years. When averaged
over the time when melting occurs (i.e. 35% of the time), the mean surface heat flux
equals 191 W m [exp. -2]. Net shortwave radiation contributes 177 W m [exp. -2], net longwave radiation
-25 W m [exp. -2], the sensible-heat flux 31 W m [exp. -2]. and the latent-heat flux 8 W m [exp. -2].

/pdf/analysis-of-a-3-year-meteorological-record-from-the-ablation-7gat5nebzu.pdf

Analysis of a 3 year meteorological record from the ablation zone of Morteratschgletscher, Switzerland : energy and mass balance

The heat and ice balances of a temperate sub-Antarctic cirque glacier were measured through the 1973–74 melt season at an altitude midway between the climatic firn limit and the snout. The melt calculated from mean daily measurements at a single level of net radiation, wind-speed, temperature, and humidity agreed with that observed at nearby budget stakes. In the central ablation zone, radiation provided (54 ± 6)% and sensible fluxes (46 ± 6)% of the heat income through the summer, which was exceptionally warm and sunny. Latent-heat fluxes made no significant contribution to the heat balance. The calculation by Smith (1960) that the radiative, sensible, and latent heat fluxes contribute about equally to ablation in this zone has not been substantiated by measurement. The measured partition of the glacier’s heat balance suggested that maritime influences on its regime are mitigated by its position in the lee of a major mountain range.

R. J. Timmis

Papers

Summer heat and ice balances on Hodges Glacier, South Georgia, Falkland Islands Dependencies