How can the GNSS radio occultations improve volcanic clouds studies?

Transcription

1 How can the GNSS radio occultations improve volcanic clouds studies? Riccardo Biondi and Lorenzo Guerrieri AXA Research Fellow, Istituto di Scienze dell Atmosfera e del Clima (ISAC-CNR) Andrea Steiner and Gottfried Kirchengast Wegener Center for Climate and Global Change (WEGC) and Institute of Physics, University of Graz Stefano Corradini, Luca Merucci and Dario Stelitano Istituto Nazionale di Geofisica e Vulcanologia (INGV) Sergio Pugnaghi University of Modena and Reggio Emilia, Chemical and Geological Sciences Department 1/15

2 Tupper et al. (2004) and Zehner (2010): use of new techniques alongside the established ones to improve the ash cloud detection/monitoring, and a reliable detection system not dependent on the meteorological conditions for weather independent warning capacity >>> ROs is a new technique for monitoring the clouds and it is weather independent IUGG (2010), only about 50% of the World's volcanoes that currently threaten air operations have any sort of ground based monitoring >>> ROs are distributed all around the world including in remote areas Zehner (2010), there is an urgent need to gather information on the vertical structure of evolving volcanic clouds >>> ROs can provide vertical information of clouds 2/15

3 R. Biondi, A. K. Steiner and G. Kirchengast, H. Brenot and T. Rieckh, A novel technique including GPS radio occultation for detecting and monitoring volcanic clouds, Atmospheric Chemistry and Physics Discussion, doi: /acp , /15

4 M. Fromm ACPD note (2016): If the post-nabro assemblage of profiles in this box is correct, then I suspect that the anomaly must be attributable to non-volcanic forcing. ACPD Editor (2016): the reviewer of the initial submission suggests that the observed temperature anomaly could be due to ENSO or QBO. ASR reviewer (2017): The paper shows that it gets warm in the stratosphere after sulfur-rich eruptions, but this is something that we already know. There was never a dispute that the eruption cloud heated the atmosphere. (!!) Corradini (2016) personal communication: due to the large uncertainties in volcanic cloud heights estimation, after reading your ACPD paper the EU reviewer of our H2020 project Advanced PRocedures for volcanic and Seismic Monitoring (APhoRISM) suggested us to include the Radio Occultations for monitoring the volcanic clouds ASR reviewer (2017): The technique proposed in this paper will only see the tops of the clouds and cannot distinguish ash from other constituents. So how useful will it be to warn airplanes of ash, which is a problem throughout the troposphere? The analysis requires separate data to detect the volcanic clouds, so the RO data do not help in detecting the clouds. 4/15

5 Volcanic cloud top detection Bending Angle Anomaly Technique GPS RO Cloud (IASI/AIRS) GPS RO CALIPSO track Bending angle Temperature Altitude above msl [km] Anomaly [Temp in K & Bending Angle in %] Bending Angle Anomaly Technique cloud top detection technique: bending angle anomaly deviation larger than 3% within a 2 km altitude range, with lower threshold at 5 km 5/15

6 Volcanic cloud top detection Volcanic cloud top determination from GPS RO for 3 different eruptions (Nabro, Puyehue and Eyjafjöll) RO-CALIOP co-locations within 200 km 10 cases (3 for Nabro and 7 for Puyehue) Correlation : 0.94 RMSE : 930 meters R. Biondi, A. K. Steiner and G. Kirchengast, H. Brenot and T. Rieckh, Supporting the detection and monitoring of volcanic clouds: a promising new application of GNSS radio occultation, Advances in Space Research, /15

7 Volcanic cloud top detection and more R. Biondi, A. K. Steiner and G. Kirchengast, H. Brenot and T. Rieckh, Supporting the detection and monitoring of volcanic clouds: a promising new application of GNSS radio occultation, Advances in Space Research, /15

8 Nabro2011, a quick story Was the eruption directly injecting into the stratosphere?? Bourassa et al., Large volcanic aerosol load in the stratosphere linked to asian monsoon transport, Science, July Fromm et al., Comment on «Large volcanic aerosol load in the stratosphere linked to asian monsoon transport», Science, February Bourassa et al., Response to Comments on «Large volcanic aerosol load in the stratosphere linked to asian monsoon transport», Science, Feb Vernier et al., Comment on «Large volcanic aerosol load in the stratosphere linked to asian monsoon transport», February Clarisse et al., The 2011 Nabro eruption, a So2 plume height analysis using IASI measurements, Atmospheric Chemistry and Physics, Fromm et al., Correcting the record of volcanic stratospheric aerosol impact: Nabro and Sarychev Peak, J. Geophys, Res., /15

9 riccardo biondi, what happened? 9/15

10 Satellite Image TIR Bands Radiance Ancillary Data - Plume Mask - Land Sea Mask Parameters (calculated a priori and related to the volcanic area, particle types, and sensor) Plume Temperature Volcanic Plume Removal (VPR) Pugnaghi et al., Real time retrieval of volcanic cloud particles and SO 2 by satellite using an improved simplified approach, Atm. Meas. Tech., Pugnaghi et al., A new simplified approach for simultaneous retrieval of SO2 and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano, Atm. Meas. Tech., Guerrieri et al., Evolution of the 2011 Mt. Etna ash and SO 2 lava fountain episodes using SEVIRI data and VPR retrieval approach, Journal of Volcanology and Geothermal Research, Plume Removed Image Computation Plume Transmittances Computation AOD, R e VPR retrieves the ash optical depth and effective radius contained in a volcanic cloud from the thermal radiance at 11 and 12 μm. First step is the estimation of Lo (clear sky radiance) removing the plume with a linear interpolation of the values found in region surrounding the plume. From Lo (clear sky radiance) and from Lm (radiance measured by the sensor) VPR computes the plume transmittance. Only the mean plume temperature (or altitude + atmospheric temperature profile) is required as input. 10/15

11 Volcanic Plume Removal intercept technique From each pixel, characterized from a couple AOD-Re, the plume transmittance and then the TOA radiance at 13.4 μm (Lz, red line) is computed for different volcanic cloud altitudes. These values are then compared with the measured TOA radiance (Lm, blue line) in the same pixel for the same wavelength. A simple linear interpolation gives the altitude for that pixel. Uncertainty! in some cases the interpolation provides results with very high errors. Volcanic Plume Removal - CO 2 slicing technique based on the strong CO 2 absorption in the μm range, using close window bands R = L o L m 34 L o L m 33 L 9 radiance measured with plume L : clear sky radiance (obtained from VPR) MODIS bands 33 and34 R z p, θ z = a a 0 cos 2 θ z + a b 0 cos θ z + a c 0 ln Z p + b a 0 cos θ z + b b Warning! The described method it is not adapt for stratospheric volcanic clouds (10-20 km) because in this case the ratio R depends mainly on the optical depth of the volcanic cloud and in a negligible way on its altitude. Dark Pixel technique The volcanic cloud altitude is obtained by comparing the Tb at 11 μm of the satellite image dark pixels, with the atmospheric temperature profile of the nearest WMO meteo station of the area of interest Prata and Grant, Determination of mass loadings and plume heights of volcanic ash clouds from satellite data, CSIRO Atmospheric Research Technical Paper No. 48, 2001 Uncertainties! Sometimes it is not possible to find the dark pixel In our study we have chosen a single dark pixel representing the cloud assuming that the cloud is flat 11/15

12 Eyjafjöll 2010 eruption case study May MODIS Terra VPR-intercept VPR-CO 2 km Altitude above msl [km] ,2km Bending angle anomaly condition satisfied! bending angle anomaly deviation larger than 3% within a 2 km altitude range, with lower threshold at 5 km Bending Angle Anomaly [%] 12/15

13 Eyjafjöll 2010 eruption case study May MODIS Aqua VPR-intercept km VPR-CO 2 Altitude abova msl [km] ,4km Bending angle anomaly condition satisfied! bending angle anomaly deviation larger than 3% within a 2 km altitude range, with lower threshold at 5 km Bending Angle Anomaly [%] 13/15

14 Cloud top comparisons Selection of 14 cases with valid estimations from GPS RO and MODIS (4 cases from MODIS Terra and 10 from MODIS Aqua) RMSE(RO-CO 2 )=1.29km RMSE(RO-DP)=2.65km RMSE(RO-IP)=1.23km RMSE less than 1km excluding this case! Radio Occultation VPR CO2 slicing VPR intercept Dark Pixel Cloud Height [km] T T T T T A A A A A A A A A Cloud observation [T=Terra A=Aqua Xdoy.hhmm] 14/15

15 Howcan the GNSS radio occultations improvevolcanic clouds studies? Due to their independence from weather conditions and to their high vertical resolution, RO observations can contribute to improved detection and monitoring of volcanic clouds and to support warning systems. We demonstrated that the bending angle anomaly technique for detecting cloud tops can be used for detecting and monitoring volcanic cloud tops. The high accuracy and vertical resolution of RO observations for detecting the tropopause with global coverage will also help to understand whether eruptions overshoot into the stratosphere and contribute to short- term climate variability. The uncertainties of different methods for determining the volcanic plume heights are still very large. At the moment the radio occultation Bending Angle Anomaly Technique is not able to distinguish within different types of clouds (meteo or volcanic) but it is able to detect them and to estimate the cloud top height with good accuracy. A big dataset of RO profiles co-located with other estimations is necessary for evaluating the performance of the Bending Angle Anomaly Technique. The results are promising showing a good agreement between the cloud top estimated by CALIOP measurements (RMSE 930m) and the cloud top estimated by MODIS with the Volcanic Plume Removal technique (RMSE 1200m). Future improvements are expected with higher temporal and spatial availability of data from new RO missions suchas COSMIC-2 andnewgnsscostellations as Galileo. 15/15

16 riccardo biondi The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/ ) under REA grant agreement n and from the AXA Research Fund.

17 3 rd International Training School on Convective and volcanic clouds detection, monitoring and modeling Tarquinia, Italy, October 2017 Participants residence Keynote lecturers Roy Gordon Grainger (Univ. Of Oxford, UK) Fred Prata (Michigan TU, USA) Dorinel Visoiu (ROMATSA, Romania) Lecturers Riccardo Biondi (ISAC-CNR, Italy) Tatjana Bolic (Univ. Of Trieste, Italy) Hugues Brenot (BIRA, Belgium) Elisa Carboni (Univ. Of Oxford, UK) Stefano Corradini (INGV, Italy) Claire Witham (MetOffice, UK) Lorenzo Labrador (MetOffice, UK) Marcello Miglietta (ISAC-CNR, Italy) Mario Montopoli (ISAC-CNR, Italy) Simona Scollo (INGV, Italy) Mark Woodhouse (Univ. Of Bristol, UK) The purpose of the School is to train outstanding students with research interest in the techniques allowing to detect, monitor, and model convective and volcanic clouds, to gain knowledge of the instruments and satellite missions (present and future) and to be able to support such kind of studies for supporting policy makers, early warning systems and aviation safety. Participants nationality Interested in the future editions of the school? Follow us here: