Transport of volcanic aerosol from the Raikoke eruption in 2019 through the Northern Hemisphere

Abstract

Volcanic injections into the upper troposphere–lower stratosphere (UTLS) affect climate by altering Earth's radiation budget and atmospheric chemistry. However, the pathways by which mid-latitude eruptions spread globally remain poorly understood. We combine nighttime Compact Optical Backscatter Aerosol Detector (COBALD) profiles over Lhasa (China) with ERA5-driven Chemical Lagrangian Model of the Stratosphere (CLaMS) backward trajectories and global three-dimensional sulfur dioxide (SO2)-based tracer simulations. With this integrated framework, we track the plume of the Raikoke eruption (21–22 June 2019) during its transport through the Northern Hemisphere and its interaction with the mature Asian Summer Monsoon Anticyclone (ASMA). Balloon-borne measurements capture the plume's arrival, vertical spreading, and dilution by air in the ASMA interior. Trajectories reveal two principal pathways from distinct Raikoke plumes: (i) an upper-level branch within the summertime stratospheric easterly flow (∼ 460–490 K) carrying the trailing filament of the vorticized volcanic plume (VVP), and (ii) a lower-level branch within the subtropical westerly jet (∼ 390–430 K) carrying the main plume. Although the ASMA can act as a transport barrier at certain potential-temperature levels, it admits mixing into the anticyclone along jet-aligned filaments and redistributes aerosols internally. We show that the transport of the volcanic plume is sensitive to parameterized mixing by varying the mixing strength in CLaMS. Portable Optical Particle Spectrometer (POPS) profiles over Boulder (USA) confirm the plume's timing and altitude, providing an independent evaluation of its transport outside the ASMA region.