Investigating the Temporal, Seasonal, and Spatial Evolution of the Atmospheric Boundary Layer Using Aerosol Backscatter Retrieval Methods

The purpose of this study is to examine and implement aerosol backscatter boundary-layer height (BLH) retrieval methods to continuously investigate the temporal, seasonal, and spatial evolution of the atmospheric boundary layer height. This study first evaluates three aerosol backscatter retrieval methods against radiosonde-derived BLHs in order to arrive at the most robust and automated method. Results demonstrated the ability of the Haar Wavelet method to more accurately detect BLHs than the other two methods tested. The Haar Wavelet was then applied to aerosol backscatter measured at a coastal site in Southeast Texas. Results showed that relatively low BLHs were associated with light-moderate onshore winds, while higher BLHs were associated with high offshore winds. Additionally, BLHs did not show a clear correlation to backward trajectories; therefore local circulations in a coastal area might largely modify turbulent properties of advected air masses and thus be of more influence in the development of the BLHs than the air mass type. Next, multiple ground-based aerosol (Light Detection And Ranging) LIDARs and one airborne LIDAR were used to analyze the spatial and temporal BLH evolution over the Houston-Galveston area. Results showed that, apart from the Galveston site, the sea breeze circulation did not have an impact on the observed BLHs as the inland progression of the sea breeze happened in the afternoon hours by the time the mixed layer was fully developed. Observed BLHs were compared with those simulated by the Advanced Research Weather Research and Forecast (ARW-WRF). Model simulations displayed an overall underestimation of BLHs with a significantly larger bias over water surfaces. Additionally, both, observations and WRF results, showed two distinct layers consisting of the near-surface sea-breeze flow, and a lofted return flow layer above. Large biases were found as the aerosol backscatter BLH was identified as the top of the return flow layer and the model derived, thermodynamically based BLH as the top of the sea breeze layer. The presence of these two layers is highly relevant. Both layers should be considered for the correct simulation of thermodynamic processes and for the vertical mixing and spatial redistribution of pollutants.