Observation and modeling of thermally induced upslope flow

Abstract

Thermally induced upslope flows were observed on several slopes and in valleys, and a simple one-layer model of upslope flow was developed. In this model, the thickness and speed of upslope flow are expressed in terms of sensible heat flux from the slope surface, drag coefficient of the slope surface, slope steepness and stability of the ambient atmosphere. Model results compare favorably with the observations. The development process in the upslope direction of a steady upslope flow was investigated with this model. A steadily developing state in the upslope direction is expressed by the dimensionless equations together with a unique parameter associated with momentum advection. The vertical distance of the slope required for well-developed upslope flow has a minimum value for a moderate slope steepness, but increases monotonously with decreasing ambient stability. The effect of unsteadiness on upslope flow was also investigated. The transient time required to reach a steady state becomes shorter with increasing ambient stability and slope steepness.