After 43?years of inactivity, the Calbuco volcano, which is located in the southern part of Chile, erupted on 22 April 2015. The space–time evolutions (distribution and transport) of its aerosol plume are investigated by combining satellite (CALIOP, IASI, OMPS), in situ aerosol counting (LOAC OPC) and lidar observations, and the MIMOSA advection model. The Calbuco aerosol plume reached the Indian Ocean 1?week after the eruption. Over the Reunion Island site (21°?S, 55.5°?E), the aerosol signal was unambiguously enhanced in comparison with background conditions, with a volcanic aerosol layer extending from 18 to 21?km during the May–July period. All the data reveal an increase by a factor of ?～??2 in the SAOD (stratospheric aerosol optical depth) with respect to values observed before the eruption. The aerosol mass e-folding time is approximately 90?days, which is rather close to the value (?～??80?days) reported for the Sarychev eruption. Microphysical measurements obtained before, during, and after the eruption reflecting the impact of the Calbuco eruption on the lower stratospheric aerosol content have been analyzed over the Reunion Island site. During the passage of the plume, the volcanic aerosol was characterized by an effective radius of 0.16?±?0.02?μm with a unimodal size distribution for particles above 0.2?μm in diameter. Particle concentrations for sizes larger than 1?μm are too low to be properly detected by the LOAC OPC. The aerosol number concentration was ?～??20 times higher that observed before and 1?year after the eruption. According to OMPS and lidar observations, a tendency toward conditions before the eruption was observed by April?2016. The volcanic aerosol plume is advected eastward in the Southern Hemisphere and its latitudinal extent is clearly bounded by the subtropical barrier and the polar vortex. The transient behavior of the aerosol layers observed above Reunion Island between May and July 2015 reflects an inhomogeneous spatio-temporal distribution of the plume, which is controlled by the localization of these dynamical barriers.
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