1. Meteor Crater Experiment (METCRAX II) Observing and modeling downslope-windstorm-type flow in a small-scale crater induced by larger-scale katabatic winds Dave Whiteman 1, Sebastian Hoch 1, Ron Calhoun 2 and Rich Rotunno 3 Background : A serendipitous discovery in a prior NSF-funded research program identified Arizona’s Meteor Crater as being ideally suited for studying Downslope-Windstorm-Type Flows (DWF), which develop there intermittently during fair weather when mesoscale nighttime drainage flows periodically cascade over the crater’s southwest rim. Many DWF replications occur naturally under these conditions in apparent response to changes in the structure of the approaching flow. 1 University of Utah, 2 Arizona State University, and 3 NCAR Project goals: Investigate the basic mechanisms leading to the evolution of downslope-windstorm-type flows Observe DWFs in Arizona’s Meteor Crater, a natural laboratory for these flows Through analysis and numerical model simulations, extend DWF knowledge to other topographic and meteorological situations

2. John Shelton photo Can existing mesoscale models produce accurate simulations of the DWF evolution at Meteor Crater and for other idealized basins and ridges of different size and shape? Will model parametric studies be successful in defining the parameter space and leading to improved understanding that will provide practical benefits for forecasting of downslope windstorms? Research Questions What is the 3-D structure of DWFs that develop behind the circular ridge of Meteor Crater? How do these 3-D flows evolve? What intermediate changes in flow structure occur as the approach flow changes? What are their characteristics and climatology? How does the crater atmosphere respond to warm air intrusions associated with the DWF? What role does the downstream stability inside the crater play in determining the penetration depth? What are the controlling upstream parameters (e.g., inversion depth and stability, wind speed and vertical shear) that cause the DWF to develop? How does blocked flow upwind of the crater rim modify the inflow? How much fluid is drawn from the upwind blocked layer as the flow goes over the rim? What meteorological mechanism produces pulses in the approach flow that tip the fluid structure into a full-fledged downslope-wind-type flow? Which of the existing theories on DWFs is responsible for DWFs at Meteor Crater?

3. Methods: The research will combine a 1-month observational program, centered on the use of three state-of-the-art scanning Doppler LiDARS, with numerical modeling of real-cases and an idealized parametric modeling study. Topography and equipment locations Measurements to be made on a SW-NE line through the crater Conceptual model based on our previous research. Streamlines, isentropes, wind and temperature profiles.