Abstract : 2D.7
Slope flows observed during METCRAX

Craig Clements, Wenqing Yao, Sharon Zhong, C. David Whiteman, Tom Horst
University of Houston

Observations from an array of five micrometeorological flux towers inside the Arizona’s Meteor Crater, which is a small, enclosed basin, were used to investigate characteristics and structures of slope flows and their interactions with the stratification of the basin and the atmospheric conditions above the basin. The towers were located along a west and east line with one at the bottom of the crater floor and two on each sidewall that has a lower slope of about 15 degree and a upper slope of 25 degree. Each tower was equipped with 3-D sonic anemometers at four levels from near surface up to 8.5 m. The month-long observations show frequent development of both upslope and downslope flows on the basin sidewalls on days with undisturbed synoptic conditions. The onset time of the nocturnal downslope flows varied from 2-3 hours before sunset on the west sidewall to 1-1.5 hour after sunset on the east sidewall, as the shadow of the sun propagated from west to east across the basin. The shadowing also caused a delay in the reversal time from downslope to upslope flows from west to east sidewall in the morning hours with an upslope flow starting within one hour following sunrise over the west slope and 2-3 hours later on the east slope. The speeds of the nocturnal drainage flows were 1-2 m s-1 with the maximum speed usually occurring within 5 m above the slope surface, while the upslope flows were slightly stronger and deeper. The study examined the oscillations of the slope flows and their relationship to variations in turbulence intensity and basin stratification, and development of the slope flows to ambient wind and stratification as represented by the observations from a tower on the crater rim.