The 2019 Raikoke volcanic eruption – Part 1: Dispersion model simulations and satellite retrievals of volcanic sulfur dioxide

Abstract

Abstract. Volcanic eruptions can cause significant disruption to society, and numerical models are crucial for forecasting the dispersion of erupted material. Here we assess the skill and limitations of the Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME) in simulating the dispersion of the sulfur dioxide (SO2) cloud from the 21–22 June 2019 eruption of the Raikoke volcano (48.3∘ N, 153.2∘ E). The eruption emitted around 1.5±0.2 Tg of SO2, which represents the largest volcanic emission of SO2 into the stratosphere since the 2011 Nabro eruption. We simulate the temporal evolution of the volcanic SO2 cloud across the Northern Hemisphere (NH) and compare our model simulations to high-resolution SO2 measurements from the TROPOspheric Monitoring Instrument (TROPOMI) and the Infrared Atmospheric Sounding Interferometer (IASI) satellite SO2 products. We show that NAME accurately simulates the observed location and horizontal extent of the SO2 cloud during the first 2–3 weeks after the eruption but is unable, in its standard configuration, to capture the extent and precise location of the highest magnitude vertical column density (VCD) regions within the observed volcanic cloud. Using the structure–amplitude–location (SAL) score and the fractional skill score (FSS) as metrics for model skill, NAME shows skill in simulating the horizontal extent of the cloud for 12–17 d after the eruption where VCDs of SO2 (in Dobson units, DU) are above 1 DU. For SO2 VCDs above 20 DU, which are predominantly observed as small-scale features within the SO2 cloud, the model shows skill on the order of 2–4 d only. The lower skill for these high-SO2-VCD regions is partly explained by the model-simulated SO2 cloud in NAME being too diffuse compared to TROPOMI retrievals. Reducing the standard horizontal diffusion parameters used in NAME by a factor of 4 results in a slightly increased model skill during the first 5 d of the simulation, but on longer timescales the simulated SO2 cloud remains too diffuse when compared to TROPOMI measurements. The skill of NAME to simulate high SO2 VCDs and the temporal evolution of the NH-mean SO2 mass burden is dominated by the fraction of SO2 mass emitted into the lower stratosphere, which is uncertain for the 2019 Raikoke eruption. When emitting 0.9–1.1 Tg of SO2 into the lower stratosphere (11–18 km) and 0.4–0.7 Tg into the upper troposphere (8–11 km), the NAME simulations show a similar peak in SO2 mass burden to that derived from TROPOMI (1.4–1.6 Tg of SO2) with an average SO2 e-folding time of 14–15 d in the NH. Our work illustrates how the synergy between high-resolution satellite retrievals and dispersion models can identify potential limitations of dispersion models like NAME, which will ultimately help to improve dispersion modelling efforts of volcanic SO2 clouds.

Improved estimation of volcanic SO<sub>2</sub> injections from satellite observations and Lagrangian transport simulations: the 2019 Raikoke eruption

“…The TROPOMI SO 2 data product provides four total vertical columns of SO 2 in mol m −2 , one for the total atmospheric column between the surface and the top of the atmosphere and three columns assuming an SO 2 layer at 1, 7, and 15 km altitude in the retrieval. The details of the retrieval are given in Theys et al (2017Theys et al ( , 2021. In studies investigating volcanic plumes, it is common to use the vertical column densities retrieved for distinct plume heights (e. g., Theys et al, 2019).…”

“…In studies investigating volcanic plumes, it is common to use the vertical column densities retrieved for distinct plume heights (e. g., Theys et al, 2019). In this study, we used the total vertical SO 2 column of the 15 km retrieval, as we considered it to provide the best approximation for the Raikoke eruption as in other studies (e. g., Muser et al, 2020;de Leeuw et al, 2021).…”

“…Compared with AIRS, the lower detection limit for TROPOMI is 0.3 DU (Theys et al, 2021) and data below this threshold are discarded in this study.…”

Identification of Smoke and Sulfuric Acid Aerosol in SAGE III/ISS Extinction Spectra Following the 2019 Raikoke Eruption

“…The 22-June, 2019 eruption was the largest volcanic eruption since 2011 (Puyehue-Cordón Caulle) and injected ≈1.5 Tg of sulfur dioxide (SO 2 ) into the lower stratosphere (Muser et al, 2020;de Leeuw et al, 2021). While the Raikoke eruption is interesting by itself, the time period surrounding the eruption is of particular interest because of coincident large wildfires in Russia and Canada (Kloss et al, 2021;Vaughan et al, 2021), resulting in the presence of smoke and volcanically derived material being present in the northern hemisphere's (NH) lower stratosphere at the same time.…”

“…Raikoke injected SO 2 and ash to a peak altitude of ≈15 km (Thomason et al, 2021), resulting in an SO 2 column density in excess of 900 Dobson units (Hedelt et al, 2019) and an overall mass load of ≈1.5 Tg (Muser et al, 2020;de Leeuw et al, 2021). This plume was transported to the northeast then down the western seaboard of North America before circling the globe (Hedelt et al, 2019;Chouza et al, 2020;Kloss et al, 2021;Vaughan et al, 2021).…”