Through its design as a turnkey, automated system for unattended, around-the-clock profiling of water vapor and aerosols, the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Raman lidar is providing a climatological database of aerosol and water vapor profiles that are being used to examine aerosol and water vapor variability over northern Oklahoma (36.606 N, 97.50 W). The diurnal and seasonal variabilities of the planetary boundary layer (PBL) height and transition zone thickness are examined using the lidar water vapor and aerosol profiles. PBL heights derived from the Raman lidar aerosol and water vapor profiles are compared with similar heights derived from radiosonde potential temperature profiles; best agreement is found during afternoon and early evening. Although the amount of total column aerosol optical thickness (AOT) varies between night and day, the lidar profiles show significant (>25%) fraction of the AOT is above the PBL layer throughout the diurnal cycle. When used in combination with backtrajectory analyses, Raman lidar water vapor and aerosol extinction measurements acquired during 2000 and 2001 show that the vertical profiles of water vapor and aerosol extinction vary with these air mass transport patterns and with aerosol optical thickness and precipitable water vapor. Aerosol optical thickness and aerosol extinction profiles simulated by the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) and Laboratoire de Météorologie Dynamique (LMD) Interaction with Chemistry and Aerosols (INCA) global aerosol models are evaluated using the Raman lidar measurements. Although these comparisons show generally good agreement in AOT, the model simulations of aerosol extinction in the lowest 1-2 km are significantly smaller than the Raman lidar measurements. Raman lidar measurements are also used in conjunction with additional ground-based and airborne in situ and remote sensing instruments deployed during the May 2003 Aerosol Intensive Operations Period (IOP) to study the long range transport of smoke from Siberian forest fires.