Lidar observations of the stratospheric aerosol layer over southern Italy in the period 1991–1995

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Abstract
Lidar measurements of the stratospheric aerosol layer have been carried out in Napoli (40°50′ N‐14°10′ E) and Potenza (40°36′ N‐15°44′ E) during the period 1991–1995, covering the history of the aerosol cloud produced by the eruption of Mount Pinatubo (June 1991, Philippines). Measurements are expressed in terms of aerosol backscattering coefficient βA(z), aerosol integrated backscattering IB and aerosol optical thickness τAat λ = 351 nm and 355 nm; βA(z) and τAare determined from a single‐wavelength elastic return. IB, τA, and βmax, the peak aerosol backscattering, reached their maximum value in December 1991, displaying a subsequent decay withe‐folding times of 237 ± 25, 250 ± 111, and 257 ± 33 days, respectively,Rmax, the peak scattering ratio, is characterized by a decay time of 235 ± 13 days. Measurements of the extinction‐to‐backscattering ratio, αA(z)/βA(z), and of the column parameter, τA/IB, allowed us to retrieve aerosol dimensional characteristics. The time evolution of the height,zc, of the aerosol cloud center of mass was also determined. Downward gravitational settling of stratospheric aerosols with time suggests aerosol particles fall within the size range 0.1–0.3 μm. An abrupt change in IB and βmaxis observed approximately 1000 days after the eruption as a result of the winter‐summer transition and the tropospheric removal of the lower portion of the stratospheric aerosol layer. Changes in the values of IB, τA/IB, andzcsuggest that this transition is characterized by a change in the aerosol mean radius from 0.3 to 0.1 μm.