Abstract : 2D.8
The development and characteristics of a cold air pool in a small, enclosed basin and its relationship with regional and large scale forcing

Crosby Savage, Sharon Zhong, Wenqing Yao, C. David Whiteman, Tom Horst, Steve Oncley
Michigan State University

Mean wind and turbulence data collected using an array of micrometeorological flux towers during the October 2007 METCRAX field campaign in Arizona’s Meteor Crater were analyzed to investigate the relationship between regional-scale ambient flows and the characteristics of temperature inversions inside the crater. The Meteor Crater is an isolated, nearly circular, completely enclosed topographic basin 1.2 kilometers in diameter and 165 meters deep with relatively uniform slopes and vegetative cover. Five micrometeorological towers were located along an east-west cross section through the center of the crater and each tower was instrumented at multiple levels with 3D sonic anemometers and krypton hygrometers that sampled continuously at 20 Hz for the entire month of the experiment. The analyses of 5-min mean data from all the towers showed that a strong temperature inversion formed inside the crater when ambient regional-scale flows were weak. Under these conditions, the temperature inversion was confined to the lowest 10-20 m above the basin floor, with the bulk of the basin atmosphere being nearly isothermal. The average inversion strength was 3-5 oC in the lowest 8 m above the basin floor, with an additional 2-4 oC temperature increase to a height of 20 m above the floor. The mean temperature difference between the floor and the rim was thus about 8 oC. Turbulence was intermittent within the temperature inversion, but was often nearly continuous in the isothermal layer above the shallow surface-based inversion. When the regional scale flows exceeded approximately 5 m/s, the basin atmosphere became fully coupled with the atmosphere above and little or no temperature inversion formed inside the crater. A regional-scale drainage flow from the southwest often formed on clear nights, producing winds of 2-7 m/s at the crater rim. Because these winds were near the threshold speed, the crater atmosphere exhibited a range of behaviors on individual nights.