Multiple-Scale Terrain Forcing of Local Wind Fields

Abstract

Observations and numerical simulations with a hydrostatic model are used to examine effects of regional and local terrain, synoptic forcing, and stability on the wind fields of an intermountain basin. The study area is centered on the Hanford site in southeast Washington. Two wintertime case studies are presented, each characterized by a surface inversion but with different synoptic forcing. In both cases, the local topography produces a region of blocked flow and significant horizontal wind shear, but slight differences in the direction of the synoptic winds lead to marked differences in the subsequent development of the wind fields over the site. Numerical experiments show that these differences are related to flow through gaps in the Cascade Mountains over 100 km to the west. Additional experiments show that a modest increase in vertical wind shear can cause significant alterations in the local flow patterns, the elimination of the blocked-flow region, and less sensitivity to regional or local terrain effects. Increased solar insulation also weakens the blocking effect of local terrain, but the effects of the Cascade Mountains can still be discerned.