Traces of Canadian Pyrocumulonimbus Clouds in the Stratosphere over Tomsk in June-July, 1991

We revise the results of lidar measurements of stratospheric aerosol over Tomsk that were made from June 29 to July 14, 1991, and initially interpreted as aerosol layers after the Pinatubo eruption. Using the NOAA HYSPLIT trajectory model, we show that the aerosol layers detected at altitudes of 12 and 14.2 km on June 29 and July 11, respectively, were the stratospheric smoke plume from massive forest fires occurring in Quebec, Canada, in June 1991. Biomass burning products reached the stratosphere via convective ascent within a pyrocumulonimbus (pyroCb) cloud that was detected at 100 km to the west of Baie-Comeau (Quebec, Canada) on June 19. The aerosol layers observed at altitudes between 11 and 16.5 km on July 8, 9, and 14 represented superpositions of the smoke plume from the Quebec pyroCb and first traces of the Pinatubo eruption.