Interaction of regional scale drainage flows with the nocturnal stable atmosphere in Arizona's Meteor Crater

Observations with a mini-SODAR, automatic temperature data-loggers, and two weather stations at Arizona's Meteor Crater in October 2009 are used to determine the characteristics of regional-scale nighttime drainage flows that produce cold air intrusions into the crater during fair weather periods. The drainage flows occur in the vicinity of the crater on terrain that slopes gently upwards toward the Mogollon Rim 30 km southwest of the crater. Drainage flows begin about 2 hours after sunset and produce jet-shaped wind profiles with maximum wind speeds of 6-8 m/s at heights of 20-30 m above the sloping plain. Because the crater's rim projects 30-50 m above the surrounding plain, the rim is directly exposed to these flows. A portion of the approaching flow that is not diverted around the crater is lifted over the rim and into the crater. The flow across the crater rim is stably stratified with a 2-5°C temperature deficit relative to the air at the rim level within the crater. Wind speeds at the crater rim vary, but are typically in the range 2-6 m/s. The cold air inflow over the crater rim descends the upwind inner sidewall as a shallow cold-air intrusion. If cold and strong enough, this inflow can penetrate to the top of a shallow surface-based inversion, causing a disturbance that produces temporary temperature increases on the crater floor. When inflow winds exceed 3.5 m/s the inversion on the crater floor becomes disturbed and may be destroyed. Lulls in the drainage flow cause the intrusion to cease and result in sudden temperature rises at the upwind rim, leading to uniform temperatures around the crater's rim.