THE EFFECTS OF AMBIENT WINDS ON VALLEY DRAINAGE FLOWS

The interaction of katabatic winds with ambient winds has been investigated for an idealized valley using Clark's nonhydrostatic model. Ambient ridgetop wind speeds ranged from 0.5 to 6 m/s, and made angles with the valley axis ranging from 0-degrees to 90-degrees; cooling of the valley was based on measured values of sensible heat fluxes taken from observations in Colorado's Brush Creek Valley. The depth and strength of the down-valley winds decreased with increasing ambient wind speeds but showed relatively little sensitivity to wind directions in the range of 10-degrees to 60-degrees from the valley axis. An observed inverse linear decrease of drainage depth with wind speed in a 100 m thick layer above the ridgetops was also found in the simulations for parts of the valley but not near the valley mouth. Vertical motions over the valley showed marked patchiness, and implications of this structure on valley flow dynamics are discussed.