Does the Asian Summer Monsoon Play a Role in the Stratospheric Aerosol Budget of the Arctic?

Abstract. The southeast Asian monsoon has a strong convectional component, with which aerosols are able to be lifted up into the lower stratosphere. Due to usually long lifetimes and long-range transport aerosols remain there much longer than in the troposphere and are also able to be advected around the globe. Our aim of this study is a synergy between modelled tropical aerosol tracers by Chemical Lagrangian Model of the Stratosphere (CLaMS) and KARL (Koldewey Aerosol Raman Lidar) at AWIPEV, Ny-Ålesund in the Arctic, by comparing back- and forward trajectories with exemplary days of Lidar measurements as well as analyse the stratospheric aerosol background. We use global 3-dimensional Lagrangian transport simulations including surface origin tracers as well as back-trajectories to identify source regions of the aerosol particles measured over Ny-Ålesund. We analysed Lidar data for the year 2021 and found the stratosphere generally clear, without obvious aerosol layers from volcanic eruptions or forest fires. Still an obvious annual cycle of the backscatter coefficient with higher values in late summer to autumn and lower values in late winter have been found. Results from CLaMS model simulations indicate that from late summer to early autumn filaments with high fractions of air which originate in South Asia – one of the most polluted regions in the world – reach the Arctic in altitudes between 360 K and 380 K potential temperature. We found a coinciding measurement between the overpass of such a filament and Lidar observations, we estimated that backscatter and depolarisation increased by roughly 15 % during this event compared to the background aerosol concentration. Hence we demonstrate that the Asian summer monsoon is a weak but measurable source for Arctic stratospheric aerosol in late summer to early autumn.