Lifting of Stable Layers Over a Circularly Symmetrical Terrain Obstacle

In the Second Meteor Crater Experiment (METCRAX II), observations were made of nocturnal katabatic flows that coursed down an extensive, gently inclined mesoscale plain to impact the Barringer Meteorite Crater. The stable air mass in the approaching katabatic flow was lifted up the 30-50 m high rim of the circularly symmetrical crater to pour over the crater's rim. The coldest air tended to build up and slow down at the lowest elevations on the upwind side of the Meteor Crater, with successive inflows being lifted over this coldest air. A "dividing streamline" separated the underlying cold air, which split around the crater at the lowest levels, from the overstreaming air that was lifted over the crater rim. The amount of lifting varied around the periphery of the crater rim, with the coldest air overflowing the rim in the direct upwind direction. Decreasing lifting and thus warmer temperatures spilled over the crater rim as angular distance increased from the upwind direction. Minor variations in rim elevation produced a secondary effect; relatively colder air passed through the lower elevation passes and gaps. The idealized circular shape of the crater simplified the investigation of the dividing streamline concept. The applicability of the concept, the variation of inflow temperatures along the crater's rim and its effect on cold air intrusions into the crater are the focus of the presentation.