An operational Raman lidar deployed at the DOE Atmospheric Radiation Measurement site in Oklahoma has collected more than 7500 h of aerosol and water vapor data between April 1998 and January 2000. These data, which span a wide variety of atmospheric conditions, have been analyzed as a function of season, integrated amount, and time of day. The scale height of the mean aerosol profiles varies considerably as both a function of season and aerosol optical thickness, with the mean scale height increasing from less than 1 km in the winter to over 2 km during turbid summer days. The mean scale height of the water vapor remained very close to 2 km, regardless of season or precipitable water vapor. Furthermore, the distribution of aerosol optical thickness shows a slight shift to smaller values at night compared to day, and the mean aerosol profiles show little diurnal dependence except at the top of the boundary layer. ¿ 2001 American Geophysical Union