Challenges in retrieving stratospheric aerosol extinction and particle size from ground-based RMR-LIDAR observations

Abstract. We report on the retrieval of stratospheric aerosol particle size and extinction coefficient profiles from multi-color backscatter measurements with the Rayleigh-Mie-Raman lidar operated at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in northern Norway. The retrievals are based on a two-step approach. In a first step the median radius of an assumed log-normal particle size distribution with fixed width is retrieved based on the color ratio formed from the measured backscatter ratios at wavelenghts of 1064 nm and 532 nm. An intrinsic ambiguity of the retrieved aerosol size information is discussed. In a second step, this particle size information is used to convert the measured lidar backscatter ratio to aerosol extinction coefficients. The retrieval is currently based on monthly-averaged lidar measurements covering the period from the year 2000 to present. A sensitivity study is presented that allows establishing an error budged for the aerosol retrievals. Assuming a log-normal aerosol particle size distribution with a geometric width of S = 1.3, median radii on the order of 100 nm are retrieved. The median radii are found to generally decrease with increasing altitude. The retrieved aerosol extinction profiles are compared to observations with various current and past satellite instruments.