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A novel technique including GPS radio occultation for detecting and monitoring volcanic clouds

TL;DR: In this paper, the volcanic cloud top altitude and the atmospheric thermal structure after volcanic eruptions are studied using Global Positioning System (GPS) Radio Occultation (RO) profiles co-located with independent radiometric measurements of ash and SO2 clouds.
Abstract: . The volcanic cloud top altitude and the atmospheric thermal structure after volcanic eruptions are studied using Global Positioning System (GPS) Radio Occultation (RO) profiles co-located with independent radiometric measurements of ash and SO2 clouds. We use the GPS RO data to detect volcanic clouds and to analyze their impact on climate in terms of temperature changes. We selected about 1300 GPS RO profiles co-located with two representative eruptions (Puyehue 2011, Nabro 2011) and found that an anomaly technique recently developed for detecting cloud tops of convective systems can also be applied to volcanic clouds. Analyzing the atmospheric thermal structure after the eruptions, we found clear cooling signatures of volcanic cloud tops in the upper troposphere for the Puyehue case. The impact of Nabro lasted for several months, suggesting that the cloud reached the stratosphere, where a significant warming occurred. The results are encouraging for future routine use of RO data for monitoring volcanic clouds.

Summary (2 min read)

3.2 AIRS and OMI Data

  • A selective detection of ash from AIRS is used in this study based on a robust volcanic ash detection method (Clarisse et al., 2013) differentiating ash from clouds, sand and other dust.
  • The AIRS ash index detection has three levels of confidence (low, medium, high).
  • A pixel with a high level of confidence indicates that the presence of ash is almost certain.
  • Note that the ash concentration is not provided and that this very selective ash detection is not effective for low ash concentrations.
  • More details about ash and SO 2 products and their limitation are reported by Brenot et al. (2014) .

3.3 CALIPSO Data

  • The authors used level 1 total attenuated backscatter products from CALIOP (CAL_LID_L1, version V3.01).
  • CALIOP attenuated backscatter data were used for detecting the ash cloud altitude with high accuracy.
  • The altitude where the attenuated backscatter at 532 nm is, from top downward, starting to be larger than the background noise is considered to be the cloud top altitude.

3.4 MODIS Data

  • MODIS is an imaging spectroradiometer flying aboard the Terra and Aqua spacecraft.
  • The wide spectral range of MODIS allows monitoring physical and optical cloud properties with global coverage (King et al., 2013) .
  • The authors used NASA MODIS Atmosphere Images Hi-Res Global Mosaic cloud data for defining clear air conditions and conditions with deep convection by using the cloud top pressure (MYD06_L2 and MOD06_L2) as reference (http://modisatmos.gsfc.nasa.gov/index.html).

4.2 Methods

  • For detecting the cloud top altitude and for analyzing the volcanic cloud structure the authors applied the anomaly technique developed by Biondi et al. (2013) for cloud top detection of convective cloud systems and cyclones.
  • The authors also computed the corresponding temperature anomaly profiles in order to assess the impact of the volcanic cloud on the atmospheric thermal structure.
  • The reference climatologies for bending angle and temperature were obtained by averaging all RO profiles collected in the period 2001 to 2012 to monthly means, using a resolution (i.e., averaging cell size) of 5° x 5° in latitude and longitude, with about 100 to 400 profiles averaged per grid cell (the specific number depending on month and latitude).

5. Results and Discussion

  • Nabro injected about 1.5 Mt SO 2 into the stratosphere that caused an enhancement of stratospheric (hydrated sulfate) aerosol (Bourassa et al., 2012; Robock, 2013) .
  • Extended aerosol layers up to 20 km altitude were measured for several months after the eruption, for the first few weeks confined over North Africa and the monsoon region due to the monsoon anticyclonic vortex and then spread over the larger Northern Hemisphere, causing warming of the lower stratosphere (Bourassa et al., 2012) .
  • The authors introduced a technique that uses as a first step observations in the thermal infrared (AIRS) and UV-visible (OMI) for identifying volcanic ash and SO 2 clouds and for discriminating against water clouds.
  • In a second step the authors use observations from GNSS RO for detecting the cloud top altitude and for analyzing the volcanic cloud structure.
  • The authors demonstrated that the anomaly technique developed by Biondi et al. (2012; 2013) for detecting cloud tops of convective systems and tropical cyclones can also be used for detecting and monitoring volcanic cloud tops.

6. Conclusions

  • These, together with a much higher number of GNSS signals from the U.S. GPS, the Russian Globalnaya navigatsionnaya sputnikovaya sistema , the European Galileo system, and the Chinese Bei-Dou system will provide RO profiles with unprecedented coverage in space and time for monitoring the thermal structure impacts of volcanic eruptions and their cloud dispersions at any stage.
  • UCAR/CDAAC (Boulder, CO, USA) is thanked for providing access to its RO excess phase and orbit data, ECMWF (Reading, UK) for access to its analysis and short-term forecast data.
  • The authors thank the WEGC processing team members for OPS development and for OPSv5.

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1
A novel technique including GPS radio occultation for detecting and 1
monitoring volcanic clouds 2
Riccardo Biondi
1
, Andrea Steiner
1
, Gottfried Kirchengast
1,2
, Hugues Brenot
3
, Therese Rieckh
1
3
1
Wegener Center for Climate and Global Change (WEGC), University of Graz, Graz, Austria
4
2
Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of
5
Graz, Graz, Austria
6
3
Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
7
8
Correspondence to: R. Biondi (riccardo@biondiriccardo.it)
9
10
Abstract
11
The volcanic cloud top altitude and the atmospheric thermal structure after volcanic
12
eruptions are studied using Global Positioning System (GPS) Radio Occultation (RO) profiles
13
co-located with independent radiometric measurements of ash and SO
2
clouds. We use the GPS
14
RO data to detect volcanic clouds and to analyze their impact on climate in terms of temperature
15
changes. We selected about 1300 GPS RO profiles co-located with two representative eruptions
16
(Puyehue 2011, Nabro 2011) and found that an anomaly technique recently developed for
17
detecting cloud tops of convective systems can also be applied to volcanic clouds. Analyzing the
18
atmospheric thermal structure after the eruptions, we found clear cooling signatures of volcanic
19
cloud tops in the upper troposphere for the Puyehue case. The impact of Nabro lasted for several
20
months, suggesting that the cloud reached the stratosphere, where a significant warming
21
occurred. The results are encouraging for future routine use of RO data for monitoring volcanic
22
clouds.
23
24
1. Introduction
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Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2015-974, 2016
Manuscript under review for journal Atmos. Chem. Phys.
Published: 19 January 2016
c
Author(s) 2016. CC-BY 3.0 License.

2
Explosive volcanic eruptions produce large ash clouds and inject huge amounts of gas, aerosol,
26
and ash into the troposphere, which can even reach into the stratosphere (Bourassa et al., 2012,
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2013; Fromm et al., 2013, 2014). Major volcanic eruptions can cause short-term climate change
28
(Robock, 2013) if sulfur dioxide (SO
2
) is injected into the stratosphere, forming sulfate aerosols
29
with a long residence time (about 1 to 3 years). The effect is a global warming of the stratosphere
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and a cooling of the troposphere as was observed for the Mount Pinatubo eruption (Robock,
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2000). The impacts largely depend on the total mass erupted, the altitude reached by the ash and
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SO
2
clouds, the location of the volcano, and the extent of the dispersion due to atmospheric
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circulation. Under favorable atmospheric conditions volcanic ash clouds can spread over
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thousands of kilometers in just a few hours.
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Ash clouds are a threat for aviation transport (Prata, 2008), since they can damage the aircraft
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engines even at large distances from the eruption. In 2010, the Eyjafjöll eruption in Iceland
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(Stohl et al., 2011) generated the largest air traffic shutdown since the Second World War with
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an estimated loss of about 3 billion dollars for the airline industry and with major effects on
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social and economic activities. Research attention focused on the improvement of detection and
40
monitoring of volcanic ash clouds, which had already been advocated by Tupper et al. (2004).
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The ESA-EUMETSAT workshop on “Monitoring volcanic ash from space” (Zehner, 2010)
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provided a list of recommendations stating that Studies should be made of potential new
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satellites and instruments dedicated to monitoring volcanic ash plumes and eruptions and
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highlighting the difficulty to monitor such events with the current knowledge.
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Observing the density of the ash cloud is one of the major challenges, since values larger than
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2 mg/m
3
are considered dangerous for aircraft engines. This parameter can only be detected by
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flying into the cloud with all related risks. The ejected mass of the eruption is fundamentally
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related to the maximum height reached by a volcanic plume (Settle, 1978). This volcanic cloud
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top altitude can be detected with different techniques (ground based, in situ, satellite), but
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typically with quite low accuracy.
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Knowledge of the cloud top altitude is essential, however, to provide information on ash-free
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altitude regions for air traffic and on potential overshooting and spread of SO
2
into the
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stratosphere, which impacts climate. The discrimination of ash clouds from other types of clouds
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is challenging, wherefore Tupper et al. (2004) state a reliable detection system cannot be
55
Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2015-974, 2016
Manuscript under review for journal Atmos. Chem. Phys.
Published: 19 January 2016
c
Author(s) 2016. CC-BY 3.0 License.

3
dependent on the meteorological conditions and it is necessary to have a weather independent
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warning capacity”. Along these lines the potential of the relatively new satellite technique of
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radio occultation (RO) based on Global Positioning System (GPS) signals, or more generally
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Global Navigation Satellite System (GNSS) signals, comes into play (Biondi et al., 2012, 2013).
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In this study we provide an assessment of the potential capacity of the RO technique for volcanic
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cloud detection and monitoring. Section 2 provides an overview of the available observing
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techniques and introduces the potentially unique role of RO data. Section 3 then summarizes the
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data sets used and section 4 the study cases (three example eruptions) and methods.
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Subsequently we discuss the results in section 5 and draw conclusions in section 6.
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2. Volcanic Cloud Observing Techniques
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Volcanic ash clouds are currently monitored by the International Airways Volcano Watch
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(IAVW) using a combination of ground-based sensors, satellite sensors, and aircraft
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measurements, but each of these methods has some temporal, spatial or technological limitation.
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According to the International Union of Geodesy and Geophysics (IUGG) only about 50% of the
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World's volcanoes that currently threaten air operations have any sort of ground-based
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monitoring (IUGG, 2010). The greatest danger for the air traffic is the time just after the eruption
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when no warnings are available, models are not reliable, and atmospheric observations are
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sporadic. The vertical resolution of most satellite data is very coarse for monitoring such kind of
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phenomena and thus there is an urgent need to gather information on the vertical structure of
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evolving volcanic clouds (Zehner, 2010).
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Geostationary satellite data (e.g., the Spinning Enhanced Visible and InfraRed Imager - SEVIRI)
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and polar satellite data (e.g., the Advanced Very High Resolution Radiometer - AVHRR, and the
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Moderate-Resolution Imaging Spectroradiometer - MODIS) are used for detecting and
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monitoring volcanic clouds (Holasek and Self, 1995; Woods et al., 1995; Prata, 2008; Clarisse et
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al., 2012; Theys et al., 2013), but they cannot profile the atmosphere vertically and
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measurements are affected by the presence of other types of clouds. Research aircraft are very
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useful for getting information about the ash extent and concentration. They provide accurate
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products, but they are not operational, the spatial coverage is limited, and technical limitations
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are the same as for commercial aircraft, i.e., they cannot fly where the ash concentration is too
85
Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2015-974, 2016
Manuscript under review for journal Atmos. Chem. Phys.
Published: 19 January 2016
c
Author(s) 2016. CC-BY 3.0 License.

4
high. Ground-based instruments such as lidars (Sawamura et al., 2012), radars (Harris and Rose,
86
1983), and cameras are also important for monitoring the eruptions, but they are too sparse and
87
with limited spatial coverage.
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Many techniques have been developed for detecting ash clouds (Prata, 2008; Clarisse et al.,
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2012) and SO
2
clouds (Prata, 2008; Theys et al., 2013) relying on different satellite
90
measurements with different resolutions such as the Global Ozone Monitoring Experiment
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(GOME-2), the Ozone Monitoring Instrument (OMI), the Infrared Atmospheric Sounding
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Interferometer (IASI), MODIS, and the Atmospheric InfraRed Sounder (AIRS). The Cloud-
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Aerosol Lidar with Orthogonal Polarization (CALIOP) on board of the Cloud-Aerosol Lidar and
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Infrared Pathfinder Satellite Observations (CALIPSO) satellite is able to profile the volcanic ash
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cloud with very high vertical resolution (Vernier et al., 2013), but the temporal resolution is not
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adequate for following the development of the plume and sometimes the discrimination of ash
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plumes from other type of clouds is problematic.
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The GNSS RO technique is highly complementary to these other systems, enabling measurement
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of atmospheric density and temperature structure in nearly any meteorological weather
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conditions, during day and night, with global coverage, and with high vertical resolution and
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high accuracy (e.g., Anthes et al., 2011; Steiner et al., 2011). Several GNSS RO missions are
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operating at present, providing vertical atmospheric profiles with good global coverage in space
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and time, like the US/Taiwan FORMOSAT-3/COSMIC six-satellite constellation (Anthes et al.,
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2008) or the European Meteorological Operational (MetOp) satellite series (Luntama et al.,
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2008).
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The use of RO data in numerical weather prediction has improved weather forecasting especially
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in remote and data sparse areas of the globe (e.g., Cardinali, 2009) as well as tropical cyclone
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track forecasting (e.g., Huang et al., 2005). Moreover, RO can deliver accurate information on
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the thermal structure and cloud top altitude of convective systems and tropical cyclones as
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demonstrated recently by Biondi et al. (2012; 2013; 2015). Monthly RO climatologies were
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recently also used, together with radiosonde and reanalysis data, in a study aiming to detect
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temperature effects of minor volcanic eruptions over 2001–2010 (Mehta et al., 2015). Due to its
113
characteristics, RO is a potentially valuable technique to study the structure of volcanic clouds
114
and to complement current monitoring systems. In this study we investigate whether the cloud
115
Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2015-974, 2016
Manuscript under review for journal Atmos. Chem. Phys.
Published: 19 January 2016
c
Author(s) 2016. CC-BY 3.0 License.

5
top detection technique developed by Biondi et al. (2013) can be applied as well for detecting
116
and monitoring volcanic clouds and for determining their cloud top height, their thermal
117
structure and influence on short-term climate.
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3. Data Sets Used
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3.1 GNSS Radio Occultation Data
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For this study we used RO temperature profiles processed by the Wegener Center for Climate
122
and Global Change (WEGC) with the Occultation Processing System (OPS) version 5.6
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(Schwärz et al., 2013), based on excess phase and orbit data version 2010.2640 from the
124
University Corporation for Atmospheric Research (UCAR). The data have a vertical resolution
125
of about 100 m in the lower troposphere to about 1 km in the stratosphere (Gorbunov et al.,
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2004). The quality of RO measurements is best in the Upper Troposphere and Lower
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Stratosphere (UTLS) with an accuracy of 0.7 K to 1 K between 8 km and 25 km for individual
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temperature profiles (Scherllin-Pirscher et al., 2011).
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RO data from the following RO missions were used: CHAllenging Minisatellite Payload
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(CHAMP) (Wickert et al., 2001), Satélite de Aplicaciones Científicas (SAC-C) (Hajj et al.,
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2004), Gravity Recovery And Climate Experiment (GRACE-A) (Beyerle et al., 2005),
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FORMOSAT-3/COSMIC, MetOP, and TerraSAR-X (Wickert et al., 2009). RO data from
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different missions are highly consistent and agree within 0.2 K between 4 km and 35 km for
134
temperature (Scherllin-Pirscher et al., 2011), which allows merging of the data without any
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calibration or homogenization (Foelsche et al., 2011; Steiner et al., 2011). Available RO data
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products include individual profiles as well as gridded climatologies (e.g., Ho et al., 2012;
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Steiner et al., 2013).
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3.2 AIRS and OMI Data
139
We used ash observations from AIRS and SO
2
observations from OMI to identify volcanic
140
clouds and to differentiate between volcanic ash clouds and SO
2
clouds (see section 4.1). AIRS
141
is a thermal infrared (IR) sensor (Aumann et al., 2003) on-board the Aqua satellite, OMI is an
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ultraviolet-visible (UV-Vis) spectrometer (Levelt et al., 2006) onboard Aura. Both polar orbiting
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satellites operate in nadir mode (with footprints of 15 km in diameter and of 13 km x 24 km,
144
Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2015-974, 2016
Manuscript under review for journal Atmos. Chem. Phys.
Published: 19 January 2016
c
Author(s) 2016. CC-BY 3.0 License.

Citations
More filters
Journal ArticleDOI
TL;DR: In this article, the Infrared Atmospheric Sounding Interferometer (IASI) on the METOP satellite was used to study volcanic emission of SO2 using high-spectral resolution measurements from 1000 to 1200 and from 1300 to 1410 cm−1 (the 7.3 and 8.7‵m SO2 bands) returning both SO2 amount and altitude data.
Abstract: . Sulfur dioxide (SO2) is an important atmospheric constituent that plays a crucial role in many atmospheric processes. Volcanic eruptions are a significant source of atmospheric SO2 and its effects and lifetime depend on the SO2 injection altitude. The Infrared Atmospheric Sounding Interferometer (IASI) on the METOP satellite can be used to study volcanic emission of SO2 using high-spectral resolution measurements from 1000 to 1200 and from 1300 to 1410 cm−1 (the 7.3 and 8.7 µm SO2 bands) returning both SO2 amount and altitude data. The scheme described in Carboni et al. (2012) has been applied to measure volcanic SO2 amount and altitude for 14 explosive eruptions from 2008 to 2012. The work includes a comparison with the following independent measurements: (i) the SO2 column amounts from the 2010 Eyjafjallajokull plumes have been compared with Brewer ground measurements over Europe; (ii) the SO2 plumes heights, for the 2010 Eyjafjallajokull and 2011 Grimsvotn eruptions, have been compared with CALIPSO backscatter profiles. The results of the comparisons show that IASI SO2 measurements are not affected by underlying cloud and are consistent (within the retrieved errors) with the other measurements. The series of analysed eruptions (2008 to 2012) show that the biggest emitter of volcanic SO2 was Nabro, followed by Kasatochi and Grimsvotn. Our observations also show a tendency for volcanic SO2 to reach the level of the tropopause during many of the moderately explosive eruptions observed. For the eruptions observed, this tendency was independent of the maximum amount of SO2 (e.g. 0.2 Tg for Dalafilla compared with 1.6 Tg for Nabro) and of the volcanic explosive index (between 3 and 5).

52 citations


Cites methods from "A novel technique including GPS rad..."

  • ..., 2014; Biondi et al., 2016). A more detailed study of the Nabro eruption, also using the C12 IASI retrieval scheme, is reported in Fromm et al. (2014), and concluded that “Nabro injected sulphur directly to or above the tropopause upon the initial eruption on 12/13 June, and again on 16 June 2011”....

    [...]

  • ..., 2014; Biondi et al., 2016). A more detailed study of the Nabro eruption, also using the C12 IASI retrieval scheme, is reported in Fromm et al. (2014), and concluded that “Nabro injected sulphur directly to or above the tropopause upon the initial eruption on 12/13 June, and again on 16 June 2011”. Here we include the Nabro summary of the C12 IASI data set. The Nabro plume is retrieved on 13 June, with a plume over north-east Africa between 14 and 18 km height. On the 14 the plume arrived over the Middle East and over central Asia on 15 June. The eruption formed two plumes at different altitudes, the higher one that reached the stratosphere and a lower one that remained confined to the troposphere with less than 10 km altitude. The higher plume is further separated into two segments, a “north” one (15 km and above) and a “south” one, a bit lower. Over all these days the plume was still attached to the volcano, indicating continuous injection. On 17 June there is a lower altitude plume and a new high altitude part going over north-east Africa. In Fromm et al. (2014) two comparisons have demonstrated the consistency of IASI altitude with other measurements: (i) morning and afternoon IASI data of the 14 June are compared with the lidar ground data at Sede Boker (Israel) and an SO2 profile from MLS (Fromm et al....

    [...]

Journal ArticleDOI
TL;DR: In this article, the altitude of volcanic clouds and the atmospheric thermal structure after volcanic eruptions are studied using Global Navigation Satellite System (GNSS) Radio Occultation (RO) profiles co-located with independent radiometer images of ash and sulfur dioxide plumes.

22 citations

References
More filters
Journal ArticleDOI
TL;DR: In this article, the authors report on ground-based lidar observations of the same event from every continent in the Northern Hemisphere, taking advantage of the synergy between global lidar networks such as EARLINET, MPLNET and NDACC with independent lidar groups and satellite CALIPSO.
Abstract: Nabro volcano (13.37°N, 41.70°E) in Eritrea erupted on 13 June 2011 generating a layer of sulfate aerosols that persisted in the stratosphere for months. For the first time we report on ground-based lidar observations of the same event from every continent in the Northern Hemisphere, taking advantage of the synergy between global lidar networks such as EARLINET, MPLNET and NDACC with independent lidar groups and satellite CALIPSO to track the evolution of the stratospheric aerosol layer in various parts of the globe. The globally averaged aerosol optical depth (AOD) due to the stratospheric volcanic aerosol layers was of the order of 0.018 ± 0.009 at 532 nm, ranging from 0.003 to 0.04. Compared to the total column AOD from the available collocated AERONET stations, the stratospheric contribution varied from 2% to 23% at 532 nm.

73 citations


"A novel technique including GPS rad..." refers background or methods in this paper

  • ...A selective detection of ash from AIRS is used in t his study based on a robust volcanic ash 152 detection method (Clarisse et al., 2013) differenti ating ash from clouds, sand and other dust. The 153 AIRS ash index detection has three levels of confid e ce (low, medium, high). A pixel with a 154 high level of confidence indicates that the presenc e of ash is almost certain. Note that the ash 155 concentration is not provided and that this very se lective ash detection is not effective for low 156 ash concentrations. More details about ash and SO 2 products and their limitation are reported by 157 Brenot et al. (2014). 158...

    [...]

  • ...Research attention focused on the improvement of detection and 40 monitoring of volcanic ash clouds, which had alread y been advocated by Tupper et al. (2004). 41 The ESA-EUMETSAT workshop on “Monitoring volcanic a sh from space” (Zehner, 2010) 42 provided a list of recommendations stating that “ Studies should be made of potential new 43 satellites and instruments dedicated to monitoring volcanic ash plumes and eruptions” and 44 highlighting the difficulty to monitor such events with the current knowledge....

    [...]

Frequently Asked Questions (1)
Q1. What are the contributions in this paper?

11 The volcanic cloud top altitude and the atmospheric thermal structure after volcanic 12 eruptions are studied using Global Positioning System ( GPS ) Radio Occultation ( RO ) profiles 13 co-located with independent radiometric measurements of ash and SO2 clouds. The authors use the GPS 14 RO data to detect volcanic clouds and to analyze their impact on climate in terms of temperature 15 changes. The authors selected about 1300 GPS RO profiles co-located with two representative eruptions 16 ( Puyehue 2011, Nabro 2011 ) and found that an anomaly technique recently developed for 17 detecting cloud tops of convective systems can also be applied to volcanic clouds. Analyzing the 18 atmospheric thermal structure after the eruptions, the authors found clear cooling signatures of volcanic 19 cloud tops in the upper troposphere for the Puyehue case. The impact of Nabro lasted for several 20 months, suggesting that the cloud reached the stratosphere, where a significant warming 21 occurred.