Collaborative Research: Structure and Evolution of Diurnal Cold-Air Pools and Seiches in Small, Closed Basins

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The meso- and micro-scale meteorology of the stable boundary layer (SBL) over mountainous terrain is one of the most challenging subjects in the applied and basic geosciences. The rapid progress in the observation and simulation (Direct Numerical Simulation, DNS; Large Eddy Simulation, LES; mesoscale modeling, MM) of the SBL in complex terrain during recent years has led to synergistic activities, which have helped close cultural gaps between meteorology and geophysics, between basic and applied research, and between the academic and operational communities. This collaborative research project will be another effort in this spirit. In contrast to other recent SBL field studies that have tried to deal with observations and simulations of very complex topography, the Principal Investigators will emphasize understanding the meso- and micro-scale structure and evolution of the SBL within, above, and in the vicinity of an ideal simple-shaped, small, closed basin cut into a nearly homogeneous plane. This research effort has been termed the Meteor Crater Experiment (METCRAX) and the site of the month-long field phase is the 1.2-km wide, 175-m deep, circularly symmetrical Meteor Crater near Winslow, Arizona. The simple terrain setting eliminates complicating factors such as advection from outside the crater and slope asymmetry, allowing the cold pool structure and evolution to be studied in a controlled manner that typically is only achieved in laboratory settings. The field observations are designed to capture (a) the mean and turbulence characteristics of the down-slope and up-slope flows into and out of the crater, (b) the diurnal cycle of buildup and breakup of the cold-air pool, (c) seiches and other waves in the cold pool, and (d) the mesoscale variability of the ambient wind, which is expected to trigger seiches and waves in the basin. The observations will span length scales from centimeters to tens of kilometers and time scales from tens of milliseconds to days. The observed data will be supplemented with state-of-the-art DNS/LES and MM simulations. This research will synthesize and advance knowledge in a variety of disciplines, including boundary-layer meteorology, mountain meteorology, the physics of atmospheric waves and instabilities, in situ and remote sensing of the lower troposphere, DNS, LES, and MM modeling, and statistical fluid mechanics. The four Principal Investigators and their co-investigators represent a well-balanced mix of observationalists and theoreticians, instrumentalists and modelers, applied and basic researchers, and meteorologists and geophysicists. This research is the first in-depth observational and computational study of seiches in a cold-air pool and is expected to lead to an enhanced understanding of the formation and breakup of cold pools that will be beneficial for a wide range of applied and theoretical problems. Between the 1990 and 2000 national censuses, the five fastest growing states were Nevada, Arizona, Colorado, Utah, and Idaho. Socioeconomic impacts of cold air pools in this region continue to grow, as well as vulnerability to climate variability. Potential benefits of this activity for society at large include improved understanding and prediction of cold pool events and the associated hazardous weather conditions and air pollution problems over the western United States. Improvements in understanding of the meteorology of these SBLs may lead to improvements in the forecasting of the onset and cessation of the cold-air pools that will have significant societal benefits and will improve the knowledge of western U.S. climate.