The 2019 Raikoke volcanic eruption – Part 1: Dispersion model simulations and satellite retrievals of volcanic sulfur dioxide
<p>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...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/10851/2021/acp-21-10851-2021.pdf |
| Summary: | <p>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 (<span class="inline-formula">SO<sub>2</sub></span>) cloud from the 21–22 June 2019 eruption of the Raikoke volcano (48.3<span class="inline-formula"><sup>∘</sup></span> N, 153.2<span class="inline-formula"><sup>∘</sup></span> E). The eruption emitted around <span class="inline-formula">1.5±0.2</span> Tg of <span class="inline-formula">SO<sub>2</sub></span>, which represents the largest volcanic emission of <span class="inline-formula">SO<sub>2</sub></span> into the stratosphere since the 2011 Nabro eruption. We simulate the temporal evolution of the volcanic <span class="inline-formula">SO<sub>2</sub></span> cloud across the Northern Hemisphere (NH) and compare our model simulations to high-resolution <span class="inline-formula">SO<sub>2</sub></span> measurements from the TROPOspheric Monitoring Instrument (TROPOMI) and the Infrared Atmospheric Sounding Interferometer (IASI) satellite <span class="inline-formula">SO<sub>2</sub></span> products.</p>
<p>We show that NAME accurately simulates the observed location and horizontal extent of the <span class="inline-formula">SO<sub>2</sub></span> 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 <span class="inline-formula">SO<sub>2</sub></span> (in Dobson units, DU) are above 1 DU. For <span class="inline-formula">SO<sub>2</sub></span> VCDs above 20 DU, which are predominantly observed as small-scale features within the <span class="inline-formula">SO<sub>2</sub></span> cloud, the model shows skill on the order of 2–4 d only. The lower skill for these high-<span class="inline-formula">SO<sub>2</sub></span>-VCD regions is partly explained by the model-simulated <span class="inline-formula">SO<sub>2</sub></span> 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 <span class="inline-formula">SO<sub>2</sub></span> cloud remains too diffuse when compared to TROPOMI measurements.</p>
<p>The skill of NAME to simulate high <span class="inline-formula">SO<sub>2</sub></span> VCDs and the temporal evolution of the NH-mean <span class="inline-formula">SO<sub>2</sub></span> mass burden is dominated by the fraction of <span class="inline-formula">SO<sub>2</sub></span> mass emitted into the lower stratosphere, which is uncertain for the 2019 Raikoke eruption. When emitting 0.9–1.1 Tg of <span class="inline-formula">SO<sub>2</sub></span> 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 <span class="inline-formula">SO<sub>2</sub></span> mass burden to that derived from TROPOMI (1.4–1.6 Tg of <span class="inline-formula">SO<sub>2</sub></span>) with an average <span class="inline-formula">SO<sub>2</sub></span> <span class="inline-formula"><i>e</i></span>-folding time of 14–15 d in the NH.</p>
<p>Our work illustrates how the synergy between high-resolution satellite retrievals and dispersion models can identify potential limitations of dispersion models like NAME,<span id="page10852"/> which will ultimately help to improve dispersion modelling efforts of volcanic <span class="inline-formula">SO<sub>2</sub></span> clouds.</p> |
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| ISSN: | 1680-7316 1680-7324 |