Evolution of the Pinatubo Aerosol: Raman Lidar Observations of Particle Optical Depth, Effective Radius, Mass, and Surface Area over Central Europe at 53.4°N

Abstract

The Raman lidar technique has been applied to document the evolution and dissipation of the Pinatubo aerosol between 1991 and 1995. For the first time, profiles of the particle extinction coefficient have been determined with lidar in the stratosphere after a major volcanic eruption. From the concurrent observation of particle backscatter and extinction, time series of surface-area and mass concentrations and surface-area-weighted mean (or effective) radius can be determined without having to assume critical aerosol input parameters. Based on these optical and physical parameters, the development of the perturbation of the stratospheric aerosol layer over central Europe is discussed. In terms of particle backscatter and mass the perturbation declined with an e-folding decay time of 14?15 months between April 1992 and April 1994. The monthly mean particle optical depth reached 0.23 in the spring of 1992. Surface-area concentrations of the order of 10?40 mm2 m?3 were observed below 20-km height for about 18 months. The effective radius increased from 0.1 to 0.2 ?m in August and September 1991 to values around 0.5 ?m in December 1991 and slowly decreased since then. The findings are compared with results of other lidar measurements in the Northern Hemisphere; balloon soundings at Laramie, Wyoming; high-altitude aircraft in situ and satellite observations (SAGE, AVHRR); and model calculations. A sedimentation model is used to analyze the mass removal from the stratosphere and the importance of different cleansing mechanisms. The comparison of the measured and simulated mass concentration profiles clearly indicate the strong impact of stratospheric?tropospheric exchange processes on the purging of aerosols from the stratosphere below 16 km.