Lidar measurements during Aerosols99

The Aerosols99 cruise (January 14 to February 8, 1999) went between Norfolk , Virginia, and Cape Town, South Africa. A Micropulse lidar system was used almost continually during this cruise to profile the aerosol vertical stru cture. Inversions of this data illustrated a varying vertical structure dep ending on the dominant air mass. In clean maritime aerosols in the Northern and Southern Hemispheres the aerosols were capped at 1 km. When a dust eve nt from Africa was encountered, the aerosol extinction increased its maximu m height to above 2 km. During a period in which the air mass was dominated by biomass burning from southern Africa, the aerosol layer extended to 4 k m. Comparisons of the aerosol optical depth (AOD) derived from lidar invers ion and surface Sun photometers showed an agreement within +/-0.05 RMS. Sim ilar comparisons between the extinction measured with a nephelometer and pa rticle soot absorption photometer (at 19 m altitude) and the lowest lidar m easurement (75 m) showed good agreement (+/-0.014 km(-1)). The lidar undere stimated surface extinction during periods when an elevated aerosol layer ( total AOD > 0.10) was present over a relatively clean (aerosol extinction < 0.05 km(-1)) surface layer, but otherwise gave accurate results.