The upslope-downslope flow transition on a basin sidewall

The late afternoon upslope-downslope flow transition on the west inner sidewall of Arizona's Meteor Crater is investigated using the observations from two micrometeorological flux towers located at different distances up the slope. The month-long METCRAX experimental campaign shows a regular upslope-downslope transition on afternoons with undisturbed synoptic conditions. The upslope-downslope transition on 22 October 2006 is visualized using time-lapse photos taken during smoke releases. The sequence of photographic images is compared with time series of surface radiative and energy budget data and mean and turbulent flow profiles from the towers. The study shows the temporal relationships among meteorological variables as the shadow cast by the crater's rim slowly propagates down the west sidewall in the late afternoon as the sun sets. The dataset clarifies the relative roles of the surface energy budget components in the loss of heat from a shallow layer above the slope that initiates a down-slope or katabatic flow. Finally, additional case studies are performed for other days to determine whether the 22 October case is representative of evening transitions on other undisturbed days.