Warm-air intrusions in Arizona's meteor crater

Episodic nighttime intrusions of warm air, accompanied by strong winds, enter the enclosed near-circular Meteor Crater basin on clear, synoptically undisturbed nights. Data analysis is used to document these events and to determine their spatial and temporal characteristics, their effects on the atmospheric structure inside the crater, and their relationship to larger-scale flows and atmospheric stability. A conceptual model that is based on hydraulic flow theory is offered to explain warm-air-intrusion events at the crater. The intermittent warm-air-intrusion events were closely related to a stable surface layer and a mesoscale (~50 km) drainage flow on the inclined plain outside the crater and to a continuous shallow cold-air inflow that came over the upstream crater rim. Depending on the upstream conditions, the cold-air inflow at the crater rim deepened temporarily and warmer air from above the stable surface layer on the surrounding plain descended into the crater, as part of the flowing layer. The flow descended up to 140 m into the 170-m-deep crater and did not penetrate the approximately 30-m-deep crater-floor inversion. The intruding air, which was up to 5 K warmer than the crater atmosphere, did not extend into the center of the crater, where the nighttime near-isothermal layer in the ambient crater atmosphere remained largely undisturbed. New investigations are suggested to test the hypothesis that the warm-air intrusions are associated with hydraulic jumps.