Atmospheric Mass Transport by Along-Valley Wind Systems in a Deep Colorado Valley

Abstract

Hourly tethered-balloon wind soundings from the 650-m deep, narrow, Brush Creek Valley of Colorado are analyzed to determine the nocturnal atmospheric mass (or volume) budget of the valley. Under the assumption that the volume flux on an entire valley cross section can be approximated from balloon soundings over the valley center, volume fluxes are calculated from tethered balloon profiles taken on 30?31 July 1982 at several points along the valley's longitudinal axis in a 7-km long segment of the valley. Down-valley volume fluxes increased in the 3 h following sunset to levels that were basically maintained through the night. Down-valley volume fluxes increased with distance down the valley axis from 0.9 million m3 s?1 at the upper end of the segment to 2.8 million m3 s?1 at the lower end, producing an average volume flux divergence of 271 m2 s?1. If we assume that the volume flux divergence is supported entirely by subsidence of air into the valley, a peak sinking rate of 0.10 m s?1 is obtained at the level of the valley's rim. Mean vertical velocity profiles through the valley's depth are calculated, and an error analysis is performed.