Lidar and SAGE II observations of Shishaldin volcano aerosols and lower stratospheric transport

During May 1999, the data collected with the two lidar systems of University of L'Aquila, Italy show an increase of the stratospheric aerosol content in the altitude range between 15 and 18km. Our first speculation is that these aerosols can be originated from the Shishaldin (Alaska) volcanic eruption of April 19, 1999. SAGE II observations, taken between Julian day 100 and 180, at latitudes above 40°N, show several sightings that are good candidates for volcanic aerosols. In absence of spatial and temporal coincidence between SAGE II and L'Aquila lidar data, the material injected by Shishaldin have been tracked with a trajectory model over short time scales. The reconstructed trajectories show that few SAGE II measurements are timely and geographically compatible with the Shishaldin eruption. In addition the aerosol growths observed by L’Aquila lidars have been also sampled by SAGE II, later and in different locations