A global climatology has been derived for different parameters characterizing the size distribution of stratospheric aerosols; the particle number density, median radius, and mode width of the particle distribution were assumed to be lognormal. Those parameters were retrieved by applying an original optical inversion scheme on Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction profiles spanning from 1984 to 2000. The specificity of the inversion algorithm resides in the use of a continuity constraint that allows one to partly get rid of the ill-posedness of the inversion problem and to greatly improve the quality and the stability of the solution. The long time period covered by the SAGE II experiment allows us to observe very different situations of volcanic load, from highly volcanic periods following major eruptions (mainly after the Pinatubo eruption of June 1991), to periods of very low aerosol load. Beyond the effects of volcanism on the aerosol parameters, other influences are observed such as seasonal effects, more particularly at midlatitude. Also the quasi-biennial oscillation (QBO) shows a clear influence on the size distribution. In this paper, we present the general features of the different aerosol profiles, and we investigate the effects of these three main influences affecting the size distribution. We present the climatology in a more quantitative way in a companion paper, by proposing reference data for the three considered aerosol parameters.