The 2019 Raikoke eruption as a testbed for rapid assessment of volcanic atmospheric impacts by the Volcano Response group

Abstract. The 21^st June 2019 Raikoke eruption (48° N,153° E) generated one of the largest amounts of sulfur emission to the stratosphere since the 1991 Mt Pinatubo eruption. Satellite measurements indicate a consensus best estimate of 1.5 Tg for the sulfur dioxide (SO₂) injected at an altitude of around 14–15 km. The peak northern hemisphere mean 525 nm Stratospheric Aerosol Optical Depth (SAOD) increased to 0.025, a factor of three higher than background levels. The Volcano Response (VolRes) initiative provided a platform for the community to share information about this eruption, which significantly enhanced coordination efforts in the days after the eruption. A multi-platform satellite observation sub-group formed to prepare an initial report to present eruption parameters including SO₂ emissions and their vertical distribution for the modelling community. It allowed to make the first estimate of what would be the peak in SAOD one week after the eruption using a simple volcanic aerosol model. In this retrospective analysis, we show that revised volcanic SO₂ injection profiles yield a higher peak injection of the SO₂ mass. This highlights difficulties in accurately representing the vertical distribution for moderate SO₂ explosive eruptions in the lowermost stratosphere due to limited vertical sensitivity of current satellite sensors (+/- 2 km accuracy) and low horizontal resolution of lidar observations. We also show that the SO₂ lifetime initially assumed in the simple aerosol model was overestimated by 66 %, pointing to challenges for simple models to capture how the life cycle of volcanic gases and aerosols depends on the SO₂ injection magnitude, latitude and height. Using revised injection profile, modelling results indicate a peak northern hemisphere monthly mean SAOD at 525 nm of 0.024, in excellent agreement with observations, associated with a global monthly mean radiative forcing of -0.17 W/m² resulting in an annual global mean surface temperature anomalies of -0.028 K. Given the relatively small magnitude of the forcing, it is unlikely that the surface response can be dissociated from surface temperature variability.