Using the WRF model to simulate the playa breeze over Dugway Proving Ground.

摘要

The aim of this model and observation based study is to investigate the Advanced Research Weather Research and Forecasting Model's (WRF-ARW, although WRF from hereout) ability to simulate the three-dimensional structure of playa breezes and drainage flows occurring in Dugway Proving Ground, Utah using sub-km nesting in addition to improved land use and terrain datasets (as compared to the default datasets provided with WRF), in addition to studying the diurnal cycle and interactions between the playa breeze and drainage flows. A playa breeze is a thermally forced air circulation system that develops near the edge of playas, which have properties distinct from the surrounding land cover, including a higher thermal conductivity, a higher albedo due to the presence of a thin salt crust at the surface, sparse vegetation cover relative to the surrounding land cover, and a higher latent heat flux. The combination of each of these characteristics produces a thermally direct circulation, with low-level flow away from the playa during the day and toward the playa at night, the result of a cooler playa during the day and a warmer playa at night. Five model runs were performed using the Noah land Surface model, each employing a four telescoping nest strategy. Each model run was given a different set of physical parameterizations, with some using GFS model output and others using NAM model output. The object behind utilizing five model runs was to isolate the impacts made by the differing model parameterization schemes used for each simulation. This was accomplished by comparing the model run output to in situ weather observations, provided courtesy of the Mountain Terrain Atmospheric Modeling and Observation Program (MATERHORN), an ongoing Multidisciplinary University Research Initiative (MURI) sponsored by the Office of Naval Research with the University of Notre Dame acting as Project Lead. It was found that each of the five model simulations tended to produce a longer lasting and stronger playa breeze than what was actually observed. Three factors are believed to be responsible for causing this to occur: synoptic scale winds in the upper atmosphere influencing model simulated winds at the surface, light wind conditions throughout the lower and upper atmosphere, which are known to cause issues in numerical model simulations, and finally a light rainfall that occurred shortly before this study's intense observation period, which acted to lower the albedo of the playa surface and thereby resulted in several of the model simulations having an initialized albedo value that did not correspond with what was actually observed. In addition to the MATERHORN collaboration, This study is also a collaboration between the University of Texas at El Paso, the U.S. Army Research Laboratory (ARL), and National Center for Atmospheric Research (NCAR).