Average Diurnal Behavior of Surface Winds during Summer at Sites in Complex Terrain

Abstract

Mean diurnal wind distributions from five surface stations in the rugged Geysers area of northern California were examined to determine how they were affected by the terrain. The one dimensional slope-flow model of Garrett was able to simulate the average diurnal wind distribution at the station with the simplest slope geometry and using only routine weather observations as input. Wind direction frequency distributions at the other four stations clearly could not be explained by a simple daytime upslope and nighttime downslope wind distribution. Winds blew perpendicular to canyon axes (simple katabatic and daytime upslop flow) or parallel to canyon axes (organized drainage and upvalley winds), depending on station location. Winds always blew upslope during the day, but at two stations the wind blew upslope on some nights and downslope on the others. The upslope flow at night may have been caused by prevailing winds in one case, and by drainage winds flowing off an opposing slope and across the intervening riverbed in the other.