Inverting for volcanic SO<sub>2</sub> flux at high temporal resolution using spaceborne plume imagery and chemistry-transport modelling: the 2010 Eyjafjallajökull eruption case study

Abstract

Abstract. Depending on the magnitude of their eruptions, volcanoes impact the atmosphere at various temporal and spatial scales. The volcanic source remains a major unknown to rigorously assess these impacts. At the scale of an eruption, the limited knowledge of source parameters, including time variations of erupted mass flux and emission profile, currently represents the greatest issue that limits the reliability of volcanic cloud forecasts. Today, a growing number of satellite and remote sensing observations of distant plumes are becoming available, bringing indirect information on these source terms. Here, we develop an inverse modelling approach combining satellite observations of the volcanic plume with an Eulerian regional chemistry-transport model (CHIMERE) to characterise the volcanic SO2 emissions during an eruptive crisis. The May 2010 eruption of Eyjafjallajökull is a perfect case study to apply this method as the volcano emitted substantial amounts of SO2 during more than a month. We take advantage of the SO2 column amounts provided by a vast set of IASI (Infrared Atmospheric Sounding Interferometer) satellite images to reconstruct retrospectively the time series of the mid-tropospheric SO2 flux emitted by the volcano with a temporal resolution of ~2 h, spanning the period from 1 to 12 May 2010. We show that no a priori knowledge on the SO2 flux is required for this reconstruction. The initialisation of chemistry-transport modelling with this reconstructed source allows for reliable simulation of the evolution of the long-lived tropospheric SO2 cloud over thousands of kilometres. Heterogeneities within the plume, which mainly result from the temporal variability of the emissions, are correctly tracked over a timescale of a week. The robustness of our approach is also demonstrated by the broad similarities between the SO2 flux history determined by this study and the ash discharge behaviour estimated by other means during the phases of high explosive activity at Eyjafjallajökull in May 2010. Finally, we show how a sequential IASI data assimilation allows for a substantial improvement in the forecasts of the location and concentration of the plume compared to an approach assuming constant flux at the source. As the SO2 flux is an important indicator of the volcanic activity, this approach is also of interest to monitor poorly instrumented volcanoes from space.

Uncertainty assessment and applicability of an inversion method for volcanic ash forecasting

“…In this study, inversion calculations with different assumed uncertainties are presented to increase understanding of the effects on the a posteriori emissions. Boichu et al (2013) investigated the SO 2 emissions of the 2010 Eyjafjallajökull eruption in early May by a similar inversion method and found that SO 2 source terms calculated with only a single satellite image gave consistent results for young plumes but showed increased uncertainty as the plume evolved. A better source term for the entire episode studied may be found by assimilating several satellite observations over the entire period studied.…”

Temporal variations of flux and altitude of sulfur dioxide emissions during volcanic eruptions: implications for long-range dispersal of volcanic clouds

“…The atmospheric dispersal of the volcanic cloud is described using the CHIMERE Eulerian chemistry-transport model (CTM; Boichu et al, 2013Boichu et al, , 2014. The model accounts for various physico-chemical processes affecting the SO 2 released in the atmosphere, including transport, turbulent mixing, diffusion, dry deposition, wet scavenging and gas/aqueous-phase chemistry.…”

“…Such favourable conditions are not always met, depending on the meteorological conditions that prevail at the time of the eruption, as well as the range of emission altitudes during the eruption. For instance, the recent May 2010 Eyjafjallajökull eruption has provided an example where the volcanic cloud transport has been shown to be less dependent on the assumed altitude of injection (Flemming and Inness, 2013;Boichu et al, 2013).…”

“…Volcanic emission flux and altitude are prone to significant variations with time, even during the course of a single volcanic event, as the type and intensity of eruptive activity are subject to dramatic changes in response to complex magmatic and hydrothermal processes taking place in the interior of the volcanic system (Petersen et al, 2012;Stohl et al, 2011;Boichu et al, 2013). Therefore, a specific strategy for determining the flux and altitude of volcanic sulfur-rich gas emissions has to be developed in order to improve the characterization of the effects of volcanism on the atmosphere.…”

“…Volcanic flux can be reconstructed using satellite imagery according to different methods involving various degrees of sophistication (Carn and Bluth, 2003;Merucci et al, 2011;Surono et al, 2012;Lopez et al, 2013;Theys et al, 2013). Among these, inverse modelling approaches are currently capable of retrieving the volcanic flux with an hourly temporal resolution using a chemistry-transport model in combination with SO 2 hyperspectral imagery (Boichu et al, 2013(Boichu et al, , 2014. These methods usually rely on independent information on the altitude of SO 2 emissions at the source in order to initialize the chemistry-transport model.…”