Abstract. Information about the height and loading of sulfur dioxide
(SO2) plumes from volcanic eruptions is crucial for aviation safety
and for assessing the effect of sulfate aerosols on climate. While
SO2 layer height has been successfully retrieved from backscattered
Earthshine ultraviolet (UV) radiances measured by the Ozone Monitoring
Instrument (OMI), previously demonstrated techniques are computationally
intensive and not suitable for near-real-time applications. In this study, we
introduce a new OMI algorithm for fast retrievals of effective volcanic
SO2 layer height. We apply the Full-Physics Inverse Learning Machine
(FP_ILM) algorithm to OMI radiances in the spectral range of
310–330 nm. This approach consists of a training phase that utilizes
extensive radiative transfer calculations to generate a large dataset of
synthetic radiance spectra for geophysical parameters representing the OMI
measurement conditions. The principal components of the spectra from this
dataset in addition to a few geophysical parameters are used to train a neural
network to solve the inverse problem and predict the SO2 layer
height. This is followed by applying the trained inverse model to real OMI
measurements to retrieve the effective SO2 plume heights. The
algorithm has been tested on several major eruptions during the OMI data
record. The results for the 2008 Kasatochi, 2014 Kelud, 2015 Calbuco, and 2019
Raikoke eruption cases are presented here and compared with volcanic plume
heights estimated with other satellite sensors. For the most part,
OMI-retrieved effective SO2 heights agree well with the lidar
measurements of aerosol layer height from Cloud–Aerosol Lidar and Infrared
Pathfinder Satellite Observations (CALIPSO) and thermal infrared retrievals of
SO2 heights from the infrared atmospheric sounding interferometer
(IASI). The errors in OMI-retrieved SO2 heights are estimated to be
1–1.5 km for plumes with relatively large SO2 signals (>40 DU). The algorithm is very fast and retrieves plume height in less
than 10 min for an entire OMI orbit.
<p>We have developed a new trajectory tool to reconstruct the altitude and the position of SO<sub>2</sub> in a volcanic plume. Starting with 2D map of satellite observed SO<sub>2</sub>, known volcano location, and reanalysis wind fields from the NASA Goddard Earth Observing System (GEOS) model, the Goddard trajectory tool allows us to estimate the altitude and concentration of SO<sub>2</sub> in the volcanic plume at time of observation. We used this tool for the June 21, 2019 Mt. Raikoke eruption and the June 15, 1991 Mt. Pinatubo event. We used SO<sub>2</sub> data from the Ozone Mapping and Profiler Suite/Nadir Mapper (OMPS/NM) onboard the NASA-NOAA Suomi satellite and obtained a distribution of SO<sub>2</sub> altitudes between 1 and 19 kilometers in different parts of the Raikoke SO<sub>2</sub> clouds, with the highest SO<sub>2</sub> concentration between 11 and 16 km, in good agreement with data from independent SO<sub>2</sub> layer height retrievals from the Ozone Monitoring Instrument (OMI) aboard the NASA Aura spacecraft; the Tropospheric Monitoring Instrument (TROPOMI) onboard the European Copernicus Sentinel 5 precursor satellite and Infrared Atmospheric Sounding Interferometer (IASI) on the European Space Agency's (ESA) MetOp series of a polar orbiting satellites. We then applied this method to the Pinatubo eruption using SO<sub>2</sub> column measurements from the NASA Total Ozone Mapping Spectrometer (TOMS) and using wind fields from the National Centers for Environmental Prediction Reanalysis version 2. We found that the southern part of the Pinatubo plume is located in the troposphere, and the northern part is in the stratosphere.</p>
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