Special Issue "Volcanic Emissions in the Atmosphere"

A special issue of Atmosphere (ISSN 2073-4433).

Deadline for manuscript submissions: closed (28 February 2019)

Special Issue Editor

Guest Editor
Dr. Mario Montopoli

Institute of Atmospheric Sciences and Climate, National Research Council of Italy, Rome branch, Italy
Website | E-Mail
Interests: remote sensing of atmospheric precipitation, active and passive microwave observations of volcanic solid emissions, ground based radars, radiative transfer models

Special Issue Information

Dear Colleagues,

Volcanic eruptions are usually characterized by the emissions of tephra particles (i.e., all kind of particles injected into the atmosphere regardless of their size, shape and composition), as well as a variety of trace gases. Volcanic ash (i.e., tephra particles less than 2 mm in size) is transported from its source through a buoyant plume that progressively spreads out to form an ash cloud, from which ash falls, and is dispersed by atmospheric processes to form deposits on the ground. Volcanic plumes and clouds are complex multi-phase environments of which the spatial and temporal evolutions are highly worth investigating for two main reasons: i) to prevent disruption to human activities and the surrounding environment, including the collapse of buildings, lifelines, and transport networks (e.g., hazards for aviation); and ii) provide an opportunity to investigate subsurface volcanic processes.

The prompt detection of explosive volcanic eruptions and the determination of eruption–column altitude and ash–cloud movement are critical factors in the mitigation of volcanic risks. Volcanic ash transport and dispersal (VATD) models can be used to mitigate the hazards posed by volcanic tephra, but their practical use requires an accurate estimate of eruption source parameters, namely the eruption plume dynamics and tephra granulometry. Nowadays, VATD models are often run using incomplete data of total grain size spectra and mass eruption rate and few studies have tried to fill this gap.

In general, retrieval of near-source parameters during the eruption phase is not an easy task because of the difficulties in direct measurements and the intrinsic space–time variability. For this purpose, several remote sensing observations are exploited. These include those based on i) the thermal infrared channels available on both Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO) satellites used to estimate the dispersal fine-ash cloud up to synoptic scales; ii) microwave (MW) channels, available on LEO satellites, occasionally used to carry additional information on the columnar content near the volcano source due to their lower opacity; iii) ground-based weather and non-weather radars used to provide a more complete view in terms of spatial and temporal sampling and estimate of source parameters in all weather conditions; iv) infrasonic arrays for eruption onset detection; v) LiDAR for fine-ash particle retrievals and cloud thickness; vi) thermal and visible cameras for plume dynamical imaging, as well as in situ measurements, such those from vii) ash collectors and size samplers (also used to characterize and assess remote sensing retrievals).

Although a convincing strategy for the full integration of the aforementioned tools into an early warning system is still lacking, many efforts are being made by the research community in this direction. The overarching goal of this Special Issue is to invite contributions from experts in the various disciplines involved in the definition of volcanic emissions in the atmosphere and source parameters. In particular, the Special Issue is focused on:

  • Satellite remote sensing tools for the detection, monitoring and quantification of volcanic emissions (e.g. sensors working in the visible, ultraviolet, infrared, and/or microwave band).
  • Ground based remote sensing for source parameters definition (e.g., radars, LiDAR, cameras, infrasounds, in situ sampling of granulometry, new instruments, etc.).
  • Volcanic ash transport and dispersal
  • Integrated warning systems for operational purposes.

In addition, this Special Issue will be the perfect place to bring together different communities working on volcanic emissions, including volcanologists, meteorologists, remote sensing experts, and model developers/users.

Dr. Mario Montopoli
Guest Editor

Manuscript Submission Information

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Keywords

  • satellite and ground based remote sensing of volcanic clouds
  • volcanic ash transport and dispersal model
  • volcanic emission integrated warning systems for operational purposes

Published Papers (1 paper)

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Research

Open AccessArticle
Passive Earth Observations of Volcanic Clouds in the Atmosphere
Atmosphere 2019, 10(4), 199; https://doi.org/10.3390/atmos10040199
Received: 6 March 2019 / Revised: 2 April 2019 / Accepted: 3 April 2019 / Published: 12 April 2019
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Abstract
Current Earth Observation (EO) satellites provide excellent spatial, temporal and spectral coverage for passive measurements of atmospheric volcanic emissions. Of particular value for ash detection and quantification are the geostationary satellites that now carry multispectral imagers. These instruments have multiple spectral channels spanning [...] Read more.
Current Earth Observation (EO) satellites provide excellent spatial, temporal and spectral coverage for passive measurements of atmospheric volcanic emissions. Of particular value for ash detection and quantification are the geostationary satellites that now carry multispectral imagers. These instruments have multiple spectral channels spanning the visible to infrared (IR) wavelengths and provide 1 × 1 km2 to 4 × 4 km2 resolution data every 5–15 min, continuously. For ash detection, two channels situated near 11 and 12 μ m are needed; for ash quantification a third or fourth channel also in the infrared is useful for constraining the height of the ash cloud. This work describes passive EO infrared measurements and techniques to determine volcanic cloud properties and includes examples using current methods with an emphasis on the main difficulties and ways to overcome them. A challenging aspect of using satellite data is to design algorithms that make use of the spectral, temporal (especially for geostationary sensors) and spatial information. The hyperspectral sensor AIRS is used to identify specific molecules from their spectral signatures (e.g., for SO2) and retrievals are demonstrated as global, regional and hemispheric maps of AIRS column SO2. This kind of information is not available on all sensors, but by combining temporal, spatial and broadband multi-spectral information from polar and geo sensors (e.g., MODIS and SEVIRI) useful insights can be made. For example, repeat coverage of a particular area using geostationary data can reveal temporal behaviour of broadband channels indicative of eruptive activity. In many instances, identifying the nature of a pixel (clear, cloud, ash etc.) is the major challenge. Sophisticated cloud detection schemes have been developed that utilise statistical measures, physical models and temporal variation to classify pixels. The state of the art on cloud detection is good, but improvements are always needed. An IR-based multispectral cloud identification scheme is described and some examples shown. The scheme is physically based but has deficiencies that can be improved during the daytime by including information from the visible channels. Physical retrieval schemes applied to ash detected pixels suffer from a lack of knowledge of some basic microphysical and optical parameters needed to run the retrieval models. In particular, there is a lack of accurate spectral refractive index information for ash particles. The size distribution of fine ash (1–63 μ m, diameter) is poorly constrained and more measurements are needed, particularly for ash that is airborne. Height measurements are also lacking and a satellite-based stereoscopic height retrieval is used to illustrate the value of this information for aviation. The importance of water in volcanic clouds is discussed here and the separation of ice-rich and ash-rich portions of volcanic clouds is analysed for the first time. More work is required in trying to identify ice-coated ash particles, and it is suggested that a class of ice-rich volcanic cloud be recognized and termed a ‘volcanic ice’ cloud. Such clouds are frequently observed in tropical eruptions of great vertical extent (e.g., 8 km or higher) and are often not identified correctly by traditional IR methods (e.g., reverse absorption). Finally, the global, hemispheric and regional sampling of EO satellites is demonstrated for a few eruptions where the ash and SO 2 dispersed over large distances (1000s km). Full article
(This article belongs to the Special Issue Volcanic Emissions in the Atmosphere)
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