Numerical Modeling of Mesoscale Airflow over Mountains

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Accurate weather forecasting in the vicinity of major mountain ranges is an extremely difficult meteorological problem. Interactions between large-scale weather systems and mountainous regions often spawn complex mesoscale weather patterns. Efforts to forecast the development of these weather patterns are limited by deficiencies in understanding of the physical processes governing mesoscale circulations in complex terrain. Additionally, mesoscale orographic effects also influence the global circulation through the action of gravity wave drag. Errors in the parameterization of gravity wave drag in global scale modes are believed to be a major source of error in extended range forecasts. Under previously supported research on this topic the Principal Investigator has found that vertically propagating mountain waves appear to be not as sensitive to the asymmetry of the underlying terrain as previously thought. Using free slip conditions, he has found that maximum lee slope winds also are not sensitive to asymmetry of the terrain. When surface friction is included, however, sensitivity to terrain is enhanced, but the primary regulator of maximum winds appears to be the steepness of the lee slope. The Principal Investigator will continue this line of research with the ultimate goal of improving weather forecasts for locations in the vicinity of mountains and to improve extended range forecasts and climate models. The major areas of concentration are: investigation of airflow in complex three-dimensional topography with emphasis on mountain barriers with and without mountain gaps, and isolated mountain peaks; study of momentum fluxes in orographically forced gravity waves and the interactions of these waves with the larger scale flow through gravity wave drag.