Near real-time assimilation of volcanic sulfur dioxide from different satellites in the MOCAGE model during volcanic eruptions

International audienceSulfur dioxide emissions during volcanic eruptions can have a significant impact on air trafic. Indeed, sulfur dioxide is a precursor of sulfuric acid which is highly corrosive and damages aircraft engines when they pass through an plume of sulfur dioxide.Currently, to predict the concentration of sulfur dioxide of volcanic origin in the French chemistry-model MOCAGE, SO2 total columns providing from TROPOMI and IASI satellites are assimilated in MOCAGE. Nevertheless, we assume that the SO2 plume is between 3 and 10km of altitude, which is not the case for all volcanic eruptions. A way to improve our analyses and the forecasts is to use information about the height of the plume.TROPOMI on Sentinel-5p is able to measure SO2 columns with high horizontal resolution from the surface to the top of the atmosphere with an information altitude of the plume for the strong total columns. The IASI instruments on Metop B and C measure total SO2 columns with a lower resolution than TROPOMI and do not give any information on the presence of volcanic SO2 below 5km altitude, but they give an information about height even for weak SO2 total columns. Height is used to constrain the altitude of plume and the thickness in the model. This presentation will give a comparison between the assimilation with and without height information on different eruptive events

Assimilation of IASI volcanic SO2 product in Chemistry Transport Model MOCAGE in support to aviation

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Near real-time assimilation of volcanic sulphur dioxide from different instruments in the MOCAGE model

International audienceSulphur dioxide emissions during volcanic eruptions can have a significant impact on air traffic. Indeed, sulphur dioxide is a precursor of sulphuric acid which is highly corrosive and damages aircraft engines when they pass through a plume of SO2. Currently, to predict the concentration of sulphur dioxide of volcanic origin in the French chemistry-transport model MOCAGE, two emission inventories from Carn are used, one for active and one for passive outgassing. However, these inventories are based on annual satellite measurements and do not cover all the volcanoes in the world. Moreover, active degassing is variable over the course of a year. A first way to improve SO2 forecasting is to use accurate information on released SO2. However, this information is not available in near real time. A second way is to use satellite information and assimilate these data in MOCAGE. TROPOMI on Sentinel-5p is able to measure SO2 columns, even for a weak signal, with high horizontal resolution from the surface to the top of the atmosphere, but it cannot give information on the total SO2 column during the night. The IASI instruments on Metop B and C measure total SO2 columns with a lower resolution than TROPOMI and do not give any information on the presence of volcanic SO2 below 5km altitude, but they can measure the total SO2 column during the day and night. The total SO2 columns from these satellites were assimilated into MOCAGE using different settings to constrain the height of the SO2 plume in the model. This presentation will give a comparison between the assimilation using some settings for the eruption of three volcanoes: the Hunga Tonga-Hunga Ha’apai , the Soufriere Saint Vincent and the Cumbre Vieja

Assimilation of satellite aerosol optical depth observations at global and regional scales in the MOCAGE CTM in operations

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A Pre-Operational System Based on the Assimilation of MODIS Aerosol Optical Depth in the MOCAGE Chemical Transport Model

International audienceIn this study we present a pre-operational forecasting assimilation system of different types of aerosols. This system has been developed within the chemistry-transport model of Météo-France, MOCAGE, and uses the assimilation of the Aerosol Optical Depth (AOD) from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard both Terra and Aqua. It is based on the AOD assimilation system within the MOCAGE model. It operates on a daily basis with a global configuration of 1∘×1∘ (longitude × latitude). The motivation of such a development is the capability to predict and anticipate extreme events and their impacts on the air quality and the aviation safety in the case of a huge volcanic eruption. The validation of the pre-operational system outputs has been done in terms of AOD compared against the global AERONET observations within two complete years (January 2018–December 2019). The comparison between both datasets shows that the correlation between the MODIS assimilated outputs and AERONET over the whole period of study is 0.77, whereas the biases and the RMSE (Root Mean Square Error) are 0.006 and 0.135, respectively. The ability of the pre-operational system to predict extreme events in near real time such as the desert dust transport and the propagation of the biomass burning was tested and evaluated. We particularly presented and documented the desert dust outbreak which occurred over Greece in late March 2018 as well as the wildfire event which happened on Australia between July 2019 and February 2020. We only presented these two events, but globally the assimilation chain has shown that it is capable of predicting desert dust events and biomass burning aerosols which happen all over the globe

Using the 3D MOCAGE CTM to simulate the chemistry of halogens in the volcanic plume of Etna's eruption in December 2018 at the regional scale

International audienceVolcanoes emit different gaseous species, SO₂ and in particular halogen species especially bromine and chlorine compounds. In general, halogens play an important role in the atmosphere by contributing to ozone depletion in the stratosphere (WMO Ozone assessment, 2018) and by modifying air composition and oxidizing capacity in the troposphere (Von Glasow et al. 2004). The halogen species emitted by volcanoes are halides. The chemical processing occurring within the plume leads to the formation of BrO from HBr following the "bromine explosion" mechanism as evidenced from both observations and modelling (e.g., Bobrowski et al. Nature, 2003; Roberts et al., Chem. Geol. 2009). Oxidized forms of chlorine and bromine are modelled to be formed within the plume due to the heterogenous reaction of HOBr with HCl and HBr, forming BrCl and Br₂ that photolyses and produces Br and Cl radicals. So far, modelling studies were mainly focused on the very local scale and processes occurring within a few hours after eruption.In this study, the objective is to go a step further by analyzing the impact at the regional scale over the Mediterranean basin of a Mt Etna eruption event. For this, we use the MOCAGE model (Guth et al., GMD, 2016), a chemistry transport model run with a resolution of 0.2°x 0.2°, to quantify the impacts of the halogens species emitted by the volcano on the tropospheric composition. We have selected here the case of the eruption of Mount Etna around Christmas 2018 characterised by large amounts of emissions over several days (Calvari et al., remote sensing 2020; Corrdadini et al., remote sensing 2020). The results show that MOCAGE represents rather well the chemistry of the halogens in the volcanic plume because it established theory of plume chemistry. The bromine explosion process takes place on the first day of the eruption and even more strongly the day after, with a rapid increase of the in-plume BrO concentrations and a corresponding strong reduction of ozone and NO2 concentrations.We also compared MOCAGE results with the WRF-CHEM model simulations for the same case study. We note that the tropospheric column of BrO and SO₂ in the two models have the same order of magnitude with more rapid bromine explosion occurring in WRF-CHEM simulations. Finally, we compared the MOCAGE results to tropospheric columns of BrO and SO2 retrieved from TROPOMI spaceborne instrument

Impact of SO2 Flux Estimation in the Modeling of the Plume of Mount Etna Christmas 2018 Eruption and Comparison against Multiple Satellite Sensors

In this study, we focus on the eruption of Mount Etna on Christmas 2018, which emitted great amounts of SO2 from 24th to 30th December into the free troposphere. Simulations based on two different estimations of SO2 emission fluxes are conducted with the chemistry-transport model MOCAGE in order to study the impact of these estimations on the volcanic plume modeling. The two flux emissions used are retrieved (1) from the ground-based network FLAME, located on the flank of the volcano, and (2) from the spaceborne instrument SEVIRI onboard the geostationary satellite MSG. Multiple spaceborne observations, in the infrared and ultraviolet bands, are used to evaluate the model results. Overall, the model results match well with the plume location over the period of the eruption showing the good transport of the volcanic plume by the model, which is linked to the use of a realistic estimation of the altitude of injection of the emissions. However, there are some discrepancies in the plume concentrations of SO2 between the two simulations, which are due to the differences between the two emission flux estimations used that are large on some of the days. These differences are linked to uncertainties in the retrieval methods and observations used to derive SO2 volcanic fluxes. We find that the uncertainties in the satellite-retrieved column of SO2 used for the evaluation of the simulations, linked to the instrument sensitivity and/or the retrieval algorithm, are sometimes nearly as large as the differences between the two simulations. This shows a limitation of the use of satellite retrievals of SO2 concentrations to quantitatively validate modeled volcanic plumes. In the paper, we also discuss approaches to improve the simulation of SO2 concentrations in volcanic plumes through model improvements and also via more advanced methods to more effectively use satellite-derived products

Halogen chemistry in Mount Etna's volcanic plume in December 2018: Comparisons between 3D MOCAGE CTM simulations and TROPOMI satellite measurements

International audienceVolcanoes are known to be important emitters of atmospheric gases and aerosols, both through explosive eruptions and persistent quiescent degassing (von Glasow et al., 2009). The most abundant gases in volcanic emissions are H2O, CO2, SO2 and halogens (HCl, HBr, HF). In general, halogens play an important role in the atmosphere by modifying air composition and oxidizing capacity in the troposphere (von Glasow et al., 2004). The chemical processes occurring within the plume lead to the formation of BrO following the 'bromine explosion' mechanism as evidenced from both observations and modelling (e.g. Bobrowski et al., 2003; Roberts et al., 2009). Oxidized forms of bromine (BrO) are formed during daytime within the plume due to heterogeneous reactions of HBr on volcanic aerosols leading to ozone depletion. So far, modelling studies mainly focused on spatial scales ranging from 10m to ~1km and processes occurring within a few hours after eruption.The objective of this study is to go a step further by analysing the impact at the regional scale namely over the whole Mediterranean basin of a single Mt Etna eruption event in December 2018. For this, we have further developed the MOCAGE model (Guth et al., 2016), a chemistry transport model run at a resolution of 0.2°× 0.2°, to quantify the impacts of the halogen species emitted by the volcano on air composition. We selected here the case of the eruption of Mt Etna around Christmas 2018 characterised by large amounts of emissions over several days. The results show that MOCAGE represents the halogen chemistry in the volcanic plume quite well. The bromine-explosion cycle takes place during the day of the eruption, with a rapid increase in BrO concentration leading to a strong depletion in ozone and NO2 concentrations across the Mediterranean as well as to changes in the air composition in particular for bromine compounds such as Br, HOBr, BrONO2, Br2 and BrCl. Adding to this, BrO is formed again on the following day (25/12/2018) during daytime from the bromine reservoir species from night time leading to additional ozone depletion.The comparison of the tropospheric columns of BrO and SO2 retrievals from the TROPOMI spaceborne instrument with the MOCAGE simulations shows that the tropospheric BrO and SO2 columns have the same order of magnitude and that the locations of the simulated and observed plumes are overall in good agreement during the main eruption period and the following six days. The comparison shows also the similarity of the order of magnitude of the BrO/SO2 ratio between MOCAGE and TROPOMI, especially for the 25th of December 2018

A regional modelling study of halogen chemistry within a volcanic plume of Mt Etna’s Christmas 2018 eruption

International audienceVolcanoes are known to be important emitters of atmospheric gases and aerosols, which for certain volcanoes can include halogen gases and in particular HBr. HBr emitted in this way can undergo rapid atmospheric oxidation chemistry (known as the bromine-explosion) within the volcanic emission plume leading to the production of bromine oxide (BrO) and ozone depletion. In this work, we present the results of a modelling study of a volcanic eruption from Mt Etna that occurred around Christmas 2018 that lasted 6 days. The aims of this study are to demonstrate and evaluate the ability of the regional 3D Chemistry Transport Model MOCAGE to simulate the volcanic halogen chemistry in this case study, to analyse the variabilit