Abstract

Long-term records of the stratospheric aerosol layer exhibit periods of low and high aerosol load. Both, the background periods and the volcanically perturbed periods, are of interest. Long-term lidar records, which cover up to two decades (e.g. DeFoor, 1993), show that the variability of the stratospheric aerosol content spans more than two orders of magnitude. Our interest is not only devoted to spectacular volcanic perturbations of the stratosphere. Of course, such events provide large signals, not only to our lidar systems, but also to atmospheric chemistry and radiation models; but the highly perturbed situation is not the normal state of the stratosphere. This is rather a state of more or less aged volcanic load. But there are also periods which are not affected by the build-up and the decay of volcanic perturbations. Such background periods have to be studied carefully to extract information on other sources of the stratospheric aerosol. Such sources might be the diffusion of sulphurous precursor gases into the stratosphere or convective processes, and, in addition, we cannot rule out sources resulting from anthropogenic activities.

© 1993 Optical Society of America