Processes of long-term relaxation of stratospheric aerosol layer in Northern Hemisphere midlatitudes after a powerful volcanic eruption

Multiyear lidar measurements of characteristics of stratospheric aerosol layer, made at midlatitude observatories in Tomsk (56.5°N, 85.0°E) and Minsk (53.9°N, 27.5°E), are analyzed and used to study the processes of long-term relaxation of the aerosol-perturbed stratosphere after powerful volcanic eruptions to background state. The absence of significant seasonal variations of vertical stratification of stratospheric aerosol and exponential altitudinal decrease of aerosol backscattering coefficient are proposed as criteria of background state of stratospheric aerosol layer for Northern Hemisphere midlatitudes.