ORCID Profile
0000-0002-6824-893X
Current Organisation
University of Oxford
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Publisher: Copernicus GmbH
Date: 17-06-2022
DOI: 10.5194/AMT-2022-166
Abstract: Abstract. Uncertainty-bounded satellite retrievals of volcanic ash cloud properties such as ash cloud-top height, effective radius, optical depth and mass loading are needed for the robust quantitative assessment required to warn aviation of potential hazards. Moreover, there is an imperative to improve quantitative ash cloud estimation due to the planned move towards quantitative ash concentration forecasts by the Volcanic Ash Advisory Centers. Here we apply the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm to Advanced Himawari Imager (AHI) measurements of the ash clouds produced by the June 2019 Raikoke (Russia) eruption. The ORAC algorithm uses optimal estimation to consolidate a priori information, satellite measurements and associated uncertainties into uncertainty-bounded estimates of the desired state variables. Using ORAC, we demonstrate several improvements in thermal infrared volcanic ash retrievals applied to broadband imagers. These include: an improved treatment of measurement noise, accounting for multi-layer cloud scenarios, distinguishing between heights in the troposphere and stratosphere, and the retrieval of a wider range of effective radii sizes than existing techniques by exploiting information from the 10.4 μm channel. Our results indicate that 0.73 ± 0.40 Tg of very fine ash (≤ 15 μm, radius) was injected into the troposphere and stratosphere during the main eruptive period from 21 June 18:00 UTC to 22 June 10:00 UTC. The total mass of very fine ash decreased from 0.73 Tg to 0.10 Tg over ~48 h with an e-folding time of 20 h. We also estimate a distal fine ash mass fraction of 0.47 ± 0.3 % based on the total mass of very fine ash retrieved and the ORAC-derived height time-series. Several distinct ash layers were revealed by the ORAC height retrievals. Generally, ash in the troposphere was composed of larger particles than ash present in the stratosphere. We also find that our implementation of the ORAC algorithm was reliable out to four days and was able to track the median ash cloud at concentrations below peak ash concentration safety limits ( 4 mg m-3) if typical ash cloud geometric thicknesses were assumed. The ORAC height retrievals for the Raikoke case study have a bias and precision of -2.22 km and 2.85 km, respectively, based on comparisons with CALIOP and GOES-17 height validation data. The dataset generated here provides uncertainties at the pixel level for all retrieved variables and could potentially be used for dispersion model validation or implemented in data assimilation schemes. Future work should focus on improving ash detection, improving height estimation in the stratosphere and exploring the added benefit of visible channels for retrieving effective radius and optical depth in opaque regions of nascent ash plumes.
Publisher: Copernicus GmbH
Date: 20-10-2022
Abstract: Abstract. Uncertainty-bounded satellite retrievals of volcanic ash cloud properties such as ash cloud-top height, effective radius, optical depth and mass loading are needed for the robust quantitative assessment required to warn aviation of potential hazards. Moreover, there is an imperative to improve quantitative ash cloud estimation due to the planned move towards quantitative ash concentration forecasts by the Volcanic Ash Advisory Centers. Here we apply the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm to Advanced Himawari Imager (AHI) measurements of the ash clouds produced by the June 2019 Raikoke (Russia) eruption. The ORAC algorithm uses an optimal estimation technique to consolidate a priori information, satellite measurements and associated uncertainties into uncertainty-bounded estimates of the desired state variables. Using ORAC, we demonstrate several improvements in thermal infrared volcanic ash retrievals applied to broadband imagers. These include an improved treatment of measurement noise, accounting for multi-layer cloud scenarios, distinguishing between heights in the troposphere and stratosphere, and the retrieval of a wider range of effective radii sizes than existing techniques by exploiting information from the 10.4 µm channel. Our results indicate that 0.73 ± 0.40 Tg of very fine ash (radius ≤ 15 µm) was injected into the atmosphere during the main eruptive period from 21 June 18:00 UTC to 22 June 10:00 UTC. The total mass of very fine ash decreased from 0.73 to 0.10 Tg over ∼ 48 h, with an e-folding time of 20 h. We estimate a distal fine ash mass fraction of 0.73 % ± 0.62 % based on the total mass of very fine ash retrieved and the ORAC-derived height–time series. Several distinct ash layers were revealed by the ORAC height retrievals. Generally, ash in the troposphere was composed of larger particles than ash present in the stratosphere. We also find that median ash cloud concentrations fall below peak ash concentration safety limits ( 4 mg m−3) 11–16 h after the eruption begins, if typical ash cloud geometric thicknesses are assumed. The ORAC height retrievals for the near-source plume showed good agreement with GOES-17 side-view height data (R=0.84 bias = −0.75 km) however, a larger negative bias was found when comparing ORAC height retrievals for distal ash clouds against Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) measurements (R=0.67 bias = −2.67 km). The dataset generated here provides uncertainties at the pixel level for all retrieved variables and could potentially be used for dispersion model validation or be implemented in data assimilation schemes. Future work should focus on improving ash detection, improving height estimation in the stratosphere and exploring the added benefit of visible channels for retrieving effective radius and optical depth in opaque regions of nascent ash plumes.
Publisher: Volcanica
Date: 03-02-2022
Abstract: Gas and particulate matter (PM) emissions from Masaya volcano, Nicaragua, cause substantial regional volcanic air pollution (VAP). We evaluate the suitability of low-cost SO2 and PM sensors for a continuous air-quality network. The network was deployed for six months in five populated areas (4–16 km from crater). The SO2 sensors failed and recorded erroneous values on multiple occasions, likely due to corrosion, requiring significant maintenance commitment. The PM sensors were found to be robust but data required correction for humidity. SO2 measurements could not be used as stand-alone tools to detect occurrence of VAP episodes (VAPE), but an SO2/PM correlation reliably achieved this at near-field stations, as confirmed by meteorological forecasts and satellite imagery. Above-background PM concentrations reliably identified VAPE at both near-field and far-field stations. We suggest that a continuous network can be built from a combination of low-cost PM and SO2 sensors with a greater number of PM-only sensors.
Publisher: Copernicus GmbH
Date: 17-11-2022
DOI: 10.5194/ACP-2022-772
Abstract: Abstract. Satellite instruments play a valuable role in detecting, monitoring and characterising emissions of ash and gas into the atmosphere during volcanic eruptions. Plumes of ash and sulfur dioxide (SO2) from the April 2021 eruption of La Soufrière volcano on St Vincent in the Eastern Caribbean were observed by a multiple satellite instruments. This study looks at these plumes with two satellite instruments: the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite (GOES), and the Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp platforms. Using true and false colour images, and brightness temperature difference images produced from the ABI data, a minimum of 32 eruptive events were identified. The ABI images were used to determine the approximate start and end times and character of each event. In this way the eruption has been ided into four phases: (1) an initial explosive event, (2) a sustained event lasting over nine hours, (3) a pulsatory phase with 23 explosive events in a 54 hour period and (4) a waning sequence of explosive events. The IASI instrument was used to study the dispersion of SO2 from this eruption. The results showed a highly complex structure to the plume, in terms of the column amounts and height, which is likely linked to the multiple explosive events. The SO2 is shown to have largely been emitted between 13 and 19 km. This was primarily in the upper troposphere and around the height of the tropopause, but with some emission into the stratosphere. The SO2 was transported around the globe with parts of the plume reaching as far as 45° S and 45° N. The largest SO2 atmospheric burden measured with IASI was 0.31±0.09 Tg, recorded on the 13 April 2021 (descending orbits). The SO2 masses were converted into fluxes. The SO2 flux was shown to peak on 10 April and then shown to decrease over time. By summing the IASI SO2 flux results, it is estimated that a total of 0.57±0.44 Tg of SO2 was emitted to the atmosphere. However, due to the limitations associated with the retrieval this should be considered a minimum estimate of the total mass of SO2 emitted. An average e-folding time of 7.09±5.70 days was computed based on the IASI SO2 results: similar to other tropical eruptions of this magnitude. There are a number of similarities between the 1979 and 2021 eruptions at La Soufrière. For ex le, both eruptions consisted of a series of explosive events with varied heights including some emission into the stratosphere. The similarities between the 1979 and 2021 highlight the importance of studying these eruptions to be prepared for future activity.
Publisher: Volcanica
Date: 03-02-2022
Abstract: Gas and particulate matter (PM) emissions from Masaya volcano, Nicaragua, cause substantial regional volcanic air pollution (VAP). We evaluate the suitability of low-cost SO2 and PM sensors for a continuous air-quality network. The network was deployed for six months in five populated areas (4–16 km from crater). The SO2 sensors failed and recorded erroneous values on multiple occasions, likely due to corrosion, requiring significant maintenance commitment. The PM sensors were found to be robust but data required correction for humidity. SO2 measurements could not be used as stand-alone tools to detect occurrence of VAP episodes (VAPE), but an SO2/PM correlation reliably achieved this at near-field stations, as confirmed by meteorological forecasts and satellite imagery. Above-background PM concentrations reliably identified VAPE at both near-field and far-field stations. We suggest that a continuous network can be built from a combination of low-cost PM and SO2 sensors with a greater number of PM-only sensors.
Publisher: Copernicus GmbH
Date: 17-11-2022
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Isabelle Taylor.