A Relative Humidity Based Comparison of Numerically Modeled Aerosol Extinction to LIDAR and Adiabatic Parameterizations
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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The lowest layer of the atmosphere is a well-mixed layer known as the planetary boundary layer PBL. Correctly characterizing the PBL is critical to being able to predict cloud formation and the extinction properties of an elevated aerosol layer. Within this layer, the size distributions, and consequently many of the scattering properties, of many aerosols are strongly affected by the relative humidity RH. Thus, in order to properly model the optical properties of the PBL, it is crucial to be able to correctly model the vertical RH profile. This research compares how well two different numerical weather prediction NWP models and a radiative transfer model can predict the relative humidity in the atmosphere. The models compared are the Global Forecast System GFS, the Weather Research and Forecasting model WRF, and the Laser Environmental Effects Definition and Reference LEEDR. The LEEDR radiative transfer model matches vertical aerosol structure observed with LIDAR measurements for the PBL, while the WRF and GFS models do not create the RH structure necessary for the observed aerosol features when run at standard resolutions. However, this research hypothesizes that increasing the vertical resolution of these models will allow them to more accurately model the RH vertical profile. To test this hypothesis, the WRF model was run at a standard vertical resolution similar to that of the GFS model, and a higher vertical resolution that included many more layers within the PBL. The comparison results are quantified in order to show which model performs the best, and the summary includes discussion on how the other models can be improved in the future.