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Stratospheric aerosol layer according to laser sensing data obtained at the Siberian Lidar Station

The report presents the results of lidar studies of dynamics of the vertical distribution of the optical characteristics of stratospheric aerosol layer (SAL), obtained at the Siberian Lidar Station of the Institute of Atmospheric Optics SB RAS (Tomsk, 56.5 degree N, 85.0 degree East) since 1986. In the report it is shown that, under background SAL conditions, the vertical aerosol distribution has no seasonal (winter-summer) variations; while the altitude behavior of aerosol backscattering coefficient is well fitted by exponential function. We think that both of these characteristics can be considered as criteria in determination of background SAL state in midlatitudes of the northern hemisphere. The level of integrated aerosol scattering in 1996 - 2000 was close to, or even less than, that in 1989 - 1990, when low aerosol content was observed in the stratosphere; this obscures somewhat the existing hypothesis that the background stratospheric aerosol mass increases by 5% per year due to anthropogenic factors. Also considered are the anomalous variations of aerosol content at altitudes above 25 km, that were observed in January-February 2000.