Volcanic sulfur dioxide total columns and layer height from the IASI and TROPOMI Layer Height products: preprocessing and assimilation on a 0.1° regional domain of MOCAGE

Abstract. Sulfur dioxide (SO₂) emitted by volcanic activity constitutes an important hazard for aircraft operations. Volcanic Ash Advisory Centres (VAACs) rely on satellite observations to monitor and on the assimilation of these observations to predict the evolution of volcanic plumes. TROPOMI (Tropospheric Monitoring Instrument) observations are already operational in the MOCAGE (Modèle de Chimie Atmosphérique à Grande Échelle) model. However, in this MOCAGE configuration, SO₂ plumes are assumed to be located between 3 and 10 km of altitude. Recent developments aim to improve SO₂ modelling by taking into account plume altitude data provided by the TROPOMI Layer Height (TROPOMI LH) product and the Infrared Atmospheric Sounding Interferometer (IASI) in the assimilation. Before being assimilated, these observations are preprocessed according to two methods depending on the assimilated instrument.

This approach is evaluated for two contrasting eruptions: the explosive eruption of Mount Etna on 4 August 2024 and the low-altitude eruption on the Reykjanes Peninsula between 22 and 25 August 2024. Independent observations from the Ozone Mapping and Profiler Suite (OMPS) and AirBase surface measurements are used for validation. The results show that the use of plume altitude improves the vertical representation of SO₂ and facilitates the detection of high SO₂ total columns. Despite the limited availability of altitude observations, their use improves plume structure and transport consistency.