Surface Roughness and Bulk Heat Transfer on a Glacier: Comparison with Eddy Correlation

Abstract

ABSTRACT. More than lOO simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness len gths of glacier ice. The results proved to be extremely se nsitive to measurement height, which is difficult to define precisely on the hummocky terrain of a glacier. Therefore, aerodynamic roughness leng th s were estimated from the microtopography of the surface, yielding 2.46 mm for ice, and 5.5 mm for snow. Despite the indeterminate nature of the profile analysis, it did support the view that the thermal roughness length must decrease as the roughness Reynolds number increases, a relationship which has been modelled in the literature. Good agreement between bulk-transfer estimates and eddy-correlation measurements of fhe sensible heat-flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length.

Surface Energy Balance Closure and Turbulent Flux Parameterization on a Mid-Latitude Mountain Glacier, Purcell Mountains, Canada

“…Conceptually, L can be thought of as the height above the surface where buoyant forces equal shear forces in the production of turbulence (Stull, 1988). As L contains Q H , an iterative scheme is used when solving Equations (4) and (22), following Munro (1989). The parameter …”

“…A small number of glacier SEB studies have attempted to measure Q H and Q L directly using the eddy covariance (EC) technique (e.g., Munro, 1989;Cullen et al, 2007;Litt et al, 2015). The installation and power requirements of this technique, along with difficulties in fulfilling the necessary measurement assumptions (outlined in Section SEB Background) have limited the use of EC systems in glacial settings, and the length of useable datasets where measurements exist.…”

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

“…Over valley or outlet glaciers, Andreas's (1987) model of z 0T has mixed performance in earlier evaluations that cover a wide range of z 0M (or Re * ) values. For instance, Munro (1989) found z 0T notably underestimated by the A87 approach over ice z 0M = 2.5 × 10 −3 m and snow z 0M = 5.5 × 10 −3 m surfaces at Peyto Glacier (Canada). A major uncertainty in Munro's work arose from the height adjustment of profile measurements, which was one possible cause of the unexpected outcome of z 0M < z 0T in Munro (1989).…”

“…For instance, Munro (1989) found z 0T notably underestimated by the A87 approach over ice z 0M = 2.5 × 10 −3 m and snow z 0M = 5.5 × 10 −3 m surfaces at Peyto Glacier (Canada). A major uncertainty in Munro's work arose from the height adjustment of profile measurements, which was one possible cause of the unexpected outcome of z 0M < z 0T in Munro (1989). Andreas (2002) re-analysed Munro's dataset and found general support for Andreas's (1987) model for aerodynamically transitional flow (Re * seldom exceeded 10, corresponding with z 0M ∼ 10 −4 m).…”

“…Critical evaluations against eddy-covariance turbulence data are truly necessary (e.g. Munro 1989;cf. Andreas 2002).…”