Dynamical influences on stratospheric aerosols observed at Aberystwyth in early 1983

An intensive study of stratospheric aerosols by means of a lidar (laser radar) was conducted at Aberystwyth (52.4°N, 4.1°W) during February and April 1983, when the optical depth due to aerosols associated with the El Chichon eruption was greatest. Very sharp vertical gradients in the aerosol backscatter profile (factors of 7 in 100 m) were found to accompany the onset and decay of a block in the tropospheric flow, and to be related to the proximity of the polar stratospheric vortex. Differential advection, identified as the process most likely to be responsible for such gradients, is suggested as a mechanism for the erosion of stratospheric vortices isolated from the pole by vigorous planetary wave activity. Statistical studies of the aerosol data reveal a time scale of 36-48 hours for temporal coherence above 17 km, corresponding to a length scale of about 300 km for the dominant irregularities in the cloud. Irregularities below 17 km were much smaller both in amplitude and scale. The observations of very sharp gradients in the aerosol cloud, facilitated by the excellent vertical resolution of the lidar technique (30 m), reveals interesting wave-like perturbations possibly caused by a gravity wave.