Valley winds in the mount Rainier area

Abstract

Four summer seasons of field work near Mt. Rainier have shown that a well-developed valley wind system tends to have the following features: Airflow within a valley is up the valley during the day and down it at night and is compensated by a return flow (anti-wind) at a higher level. The layers occupied by the two flows are of approximately equal thickness, and the boundary between them is generally at, or somewhat below, ridgeheight. Above the anti-wind, the flow depends on the large-scale synoptic situation. Horizontal wind speed in these two layers is greatest slightly below the center of each layer. Speeds reach a maximum in early afternoon and just beforce sunrise. The reversal between day and nighttime flows is almost simultaneous everywhere in the valley, about an hour after sunnet and sunrise. Vertical transport of air between the two layers appears to be localized, mainly in the neighborhood of the ridges. Slope winds apparently feed the vertical currents. Speed fluctuations, having a period of about 20 minutes, were observed in drainage winds near the surface at night. When a well-developed wind system occured in one valley, well-developed systems tended to occur in other valleys in the same area.