LAUSR

As part of the Southeast United States based Studies of Emissions & Atmospheric Composition, Clouds & Climate Coupling by Regional Surveys (SEAC4RS), and collinear with part of the Southeast Atmosphere Study (SAS), the University of Wisconsin High Spectral Resolution Lidar (UW-HSRL) system was deployed to the University of Alabama from June 19th through November 4th, 2013. With a collocated Aerosol Robotic NETwork (AERONET) sun photometer, a nearby Chemical Speciation Network (PM2.5) measurement station, and near daily ozonesonde releases for the August-September SEAC4RS campaign, the site allowed the region's first comprehensive diurnal monitoring of aerosol particle vertical structure. A 532 nm lidar ratio of 55 sr provided good closure between aerosol backscatter and AERONET Aerosol Optical Thickness (AOT). A principle component analysis was performed to identify key modes of variability in aerosol backscatter. “Fair weather” days exhibited classic planetary boundary layer (PBL) structure of a mixed layer accounting for ~50% of AOT and an entrainment zone providing another 25%. An additional 5-15% of variance is gained from the lower free troposphere from either convective detrainment or frequent intrusions of Western United States biomass burning smoke. Generally aerosol particles were contained below the 0o C level, a common level of stability in convective regimes. However, occasional strong injections of smoke to the upper troposphere were also observed, accounting for the remaining 10-15% variability in AOT. Examples of these common modes of variability in frontal and convective regimes are presented, demonstrating why AOT often has only a weak relationship to surface PM2.5 concentration.