Local Effects On Icing Forecasts for Wind Power In Cold Climate

Abstract: This thesis will examine the local effects of land cover on icing forecasts. In Paper I, a single column model was used to test the sensitivity of icing forecasts to land cover fraction. Here, the ice accretion forecast was found to be highly sensitive to the wind magnitude response to the surface roughness. Diabatic effects related to the surface albedo played a secondary role, significant in cases with strong solar irradiance. Paper II examined the impact of 2-dimensional patterns of land cover heterogeneity on the effective surface roughness and blending height using large eddy simulation over a diurnal cycle of solar irradiance. The blending height--or the elevation at which the atmospheric response to the underlying land cover becomes horizontally homogeneous--has been proposed as a guide for coupling numerical weather models to surface parameterizations. In stable conditions, when the atmospheric boundary layer height was shallow, the blending height over surfaces with large heterogeneity length scale was found to be much lower than that of analytical models from previous studies. A new formula for a dynamic blending height was proposed taking this effect into account. The effective surface roughness was found to decrease with increasing land cover heterogeneity. The wind power response from an idealized wind turbine with 80-meter hub height to the effective surface roughness was shown, with a positive response in wind power with increasing land cover heterogeneity. The wind power response was smaller and less systematic with wind turbines extending above the blending height, further highlighting the utility of an accurate formulation for this variable.