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A Down-valley Low-level Jet Event During T-REX 2006

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A prolonged down-valley flow and low-level jet was observed throughout the Enhanced Observing Period 4 Apr 28-29 of the 2006 Terrain-induced Rotor Experiment, held in the Owens Valley of California near the town of Independence. The low-level jet was strongest during the nocturnal hours, and special field observations captured important details of the event lifecycle. High resolution simulations using the Weather Research and Forecasting numerical weather prediction NWP model were generated, with underlying assumptions being that model resolution, boundary layer physics, and nesting configuration would be dominant controlling factors in reproducing the jet. The large-scale conditions were dry throughout the event, so moist physics were not a significant forcing consideration. For the control simulation, a two-nest 4.5 km and 1.5 km grid spacing configuration with 90 vertical levels was applied. Additionally, the Quasi-Normal Scale Elimination planetary boundary and surface layer option was selected due to its published performance under conditions of stable stratification. Three other sensitivity simulations were run for comparison, differing from the control just in the choice of vertical resolution 60 versus 90 levels with Quasi-Normal Scale Elimination and planetary boundarysurface layer physics 90 levelsMellor-Yamada- Jancic 90 levelsYonsei State University. Although the gross evolution location, height, and timing of the low-level jet is captured by all model runs with the 1.5 km inner nest providing the more accurate details, there were at times large underestimations of the nocturnal jet speed max in each simulation approaching 100 error, or up to almost 10 m s-1.

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  • Meteorology
  • Numerical Mathematics

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