| Description |
The Meteor Crater Experiment (METCRAX), conducted in the Arizona Meteor Crater near Winslow, AZ, aimed to better understand cold air pool evolution within the idealized topography of the crater. The October 2006 experimental period had seven intensive observational periods (IOPs) with supplemental tethersonde and radiosonde launches. Vertical temperature profiles throughout the cold pool formation, maintenance, and breakup periods were taken within the crater atmosphere and outside on the gently sloping plain. Temperature dataloggers along the slopes of the crater provided additional information on the three-dimensional temperature structure of the crater atmosphere. The diurnal evolution of the crater and plain atmospheres was compared qualitatively to determine differences in boundary layer structure evolution, and compared quantitatively to evaluate the topographic amplification factor (TAF), which is used to characterize impacts of the crater topography on nighttime cooling. At night, the nocturnal crater atmosphere formed a three-layer temperature structure. A strong shallow surface inversion formed on the floor of the crater up to a height of about 30 m. A nearly isothermal layer developed above this and extended to the crater rim about 165 m above the crater floor. This was surmounted by a capping inversion that deepened and strengthened during the course of the night, eventually extending 50 m above the crater rim, with a residual layer above. The crater atmosphere continued to cool throughout the night while maintaining its isothermal stability, in contrast to previous observations in other similar size basins where atmospheric stability increased throughout the night. The basin inversion was destroyed over a period of several hours after sunrise from subsidence warming and growth of the convective boundary layer from the heated surface. Comparisons between different temperature datasets indicate that the crater is not consistently horizontally homogeneous. On two undisturbed experimental nights total volume-weighted cooling was found to be similar for the crater and plain atmospheres, while on a disturbed night a larger bulk cooling occurred within the crater. The nearly equal volume-weighted cooling within the crater and over the plain on undisturbed nights is the first experimental confirmation of the topographic amplification factor concept. |
