Compact Airborne Raman Lidar Measurements of Fine Water Vapor Structure in Boundary Layer over Northern Colorado and Comparison with WRF Simulations

Accurate modeling of the atmospheric boundary layer (ABL) in mountainous terrain is one of the major challenges in weather prediction models. Boundary layer modeling is essential in assessing renewable energy availability. Conducting comparisons with observational data is a way to determine the shortcomings and strengths of different boundary layer schemes within these models. Lidars have long been one of the primary instruments to profile the ABL and to provide high temporally and spatially resolved data to compare with model outputs. On the afternoon of June 21, 2010, the University of Wyoming King Air, equipped with a Compact Airborne Raman Lidar as well as various in situ instruments, conducted research flights over the Northern Colorado Front Range and Southern Wyoming as part of the Wyoming King Air PBL Exploratory Experiment (KAPEE). The Raman lidar provide fine water vapor structure below the flight level and aerosol structure within the ABL. Water vapor structure showed a sharp transition between the moist boundary layer to the east of the mountains and the dryer boundary layer to the west. There were two contributing factors to this moist boundary. First, there was a stationary front along the mountains. Second, the diurnal heating induced anabatic winds acted to push the moist air up the mountain slope from the plains below. The Advanced Research Weather Research and Forecasting (ARW or WRF) Model was used to simulate the case and WRF results were compared with the observations collected by the instruments on board the King Air. Simulations with the Mellor-Yamada-Janjic (MYJ), Yonsei University PBL (YSU), and ACM2 boundary layer parameterizations were performed. The comparisons with the King Air observations clearly show the strengths and weaknesses of different ABL parameterization in mountainous terrain. These results can be utilized to improve boundary layer schemes for mountainous terrain in order to improve forecasts and assessments of renewable energy for those regions.