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R. G. Wilson and D. E. Petzold

Abstract

A mathematical model is presented which is used to calculate the flux of solar radiation to a melting snowpack in sub-arctic woodlands. Using tree height, branch radius, and distance between trees as input data, the model calculates both hemispherical and angular view factors. The latter are checked by a special photographic technique and good agreement is obtained. The view factors are used in conjunction with measurements of global and diffuse solar radiation at a base station to calculate the corresponding fluxes in nearby woodland. A test of the model at Schefferville, Quebec, showed that calculated and observed values were highly correlated, although the model consistently produced slight underestimates.

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G. Szeicz, D. E. Petzold, and R. G. Wilson

Abstract

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G. Szeicz, D. E. Petzold, and R. G. Wilson

Abstract

In the subarctic region of central Labrador wind speeds were measured at 2 m height in open lichen woodlands of various stand densities and were related to standard winds recorded at the same level on the local airport site. The resulting reduction in wind speeds are shown to be closely related to stand parameter h * which is a function of average tree height, stand density and shrub cover; variables that can easily be obtained from airphotos or from direct ground surveys. The equation giving the ratio of wind in the woodland u(s)to that measured at the air field u(s) is u(s)=u(s)(1+βh *)−2 with β=1.16 for s=2, and s=2.0 m. The equation seems applicable to various types of stands that do not streamline in wind, ranging from open lichen cover without trees, to a dense but leafless deciduous winter hardwood forest stand. For the typical and geographically widespread open lichen woodland of the subarctic, h * was related to the usual silvicultural measure of trunk diameter at breast height (DBH) offering a useful short cut in possible ground surveys.

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