Motion of volcanic plumes Contribution to the Support to Aviation Control Service Thilo Erbertseder, DLR Werner Thomas, DWD Michel van Roozendael, BIRA Dimitris Balis, Uni Thessaloniki Cristos Zerefos, Uni Athens

Scope Tasks within SACS: Determination and delivery of trajectories for analysis and warning system

Objectives To facilitate interpretation of satellite observations To attribute observations of increased SO2 to a particular volcano To forecast motion of plumes To supplement and improve the NRT monitoring and warning system

Methods applied Operational use: 3D Trajectories (Flextra, Stohl et al.) Trajectory Matching Technique Case studies: Particel Dispersion Modelling (Flexpart, Stohl et al.)

Mt. Etna SO2 SCIAMACHY + MERIS: 29th October 2002

Why watching the Etna with GOME ? GOME is designed for to measure the content of atmospheric trace species, among them SO2 SO2 forms sulphate aerosol in the stratosphere and is responsible for the “acid rain” phenomenon in the troposphere Volcanoes are the major source of natural sulphur dioxide emissions The stratovolcano Etna is the most active volcano in Europe Especially, Etna is one of the major global sources of SO2 There were two severe eruptions of Etna in Summer 2001 and Autumn 2002 Is GOME suited for doing this job ? What can we expect for GOME-2/MeTop ?

Monitoring and Forecasting SCIA: SO2 / MERIS: VIS Trajectory Analysis Particle Dispersion

FLEXTRA (Stohl and Seibert, 1998) 3D Trajectories (u,v,w) Trajectory Model Used FLEXTRA (Stohl and Seibert, 1998) 3D Trajectories (u,v,w) Driven by ECMWF analyses and forecasts Validated by Gas balloon tracks from the Gordon Benett Cup (Baumann and Stohl, 1997) – horizontal movement Tracer Experiments (ETEX, ANATEX) Dynamical tracers (PV) Position error ~20% (48h) (Stohl, 1998)

Trajectory Model Used Intercomparison of TRAJKS (KNMI), LAGRANTO (ETH Zurich) and FLEXTRA (TU Munich) Models agree well based on same windfields Agreement of two runs of the same model with different wind field frequencies (3h and 6h) is worse than the agreement between different models with the same time resolution Average horizontal position deviation after 48h is <4% Equally efficient use of wind field information

Trajectory Matching Technique Allows attribution of observations of increased SO2 levels to a particular volcano/source Allows determination of effective emission height at volcano and plume height estimate anywhere Enables to better derive AMFs Enables forecasting of plume motion

Trajectory Matching Technique If a pixel with elevated SO2 content is detected Calculation back trajectories at different altitudes Attribution to particular volcanic source Matching trajectory gives first estimate of plume height Calculation of forward trajectory from source Confirmation of plume height w. r. t SO2 observation Forecasting of plume motion w.r.t to plume height and SO2 observation

TMT 1: detection of increased SO2 levels July 25, 2001 GOME narrow scan mode Orbit 32741 gives impression of GOME-2 spatial resolution

TMT 2: Backward Trajectories

TMT 3: Iteration with FWD trajectories

TMT 4: Confirmation of source Iterative process allows attribution to particular volcano or other source allows estimate of plume height (+/- 0,5 km) allows estimate of effective emission height at volcano

TMT 5: Forecasting of plume motion Motion of air parcel can be derived One trajectory is provided 72 hour forecast Validation by comparison with upcoming meteorological analyses and satellite observations

TMT: Estimation of plume height to improve AMF AMF @ 320 nm SZA 45°

TMT: Estimation of plume height to improve AMF Quality of SO2 retrieval depends strongly on a priori knowledge about the SO2 profile the aerosol parameters (AOT, type)

Validation of GOME SO2 retrieval

Validation of GOME SO2 retrieval Initialisation, October 31, 12 UTC

Justification of aerosol loading by LIDAR measurements Thessaloniki Lidar Arrival of volcanic aerosol over Thess. on November 1/2, 2002 at ~ 5000 m a.s.l. Vertical thickness ≈ 1km

Validation by Brewer measurements This is the amount derived from GOME Average increase of SO2 content from 31st Oct to 2nd Nov 2002 is about 3 DU This is the amount derived from GOME Thessaloniki/Greece   3 DU 31st- Oct 2002 2nd- Nov 2002

Conclusion on GOME SO2 retrieval GOME is able to measure volcanic SO2 but needs external information about plume height and aerosol loading to do it with reasonable accuracy of < 30% Sensitivity to PBL SO2 limited, but will improve with GOME-2 (spatial resolution) Thomas, Erbertseder, van Roozendael et al., J. Atm. Chem. 2005

Lagrangian Particel Dispersion Modelling Applied as tool to evaluate satellite observations Combination with ground-based measurements of SO2 emissions, the spatial and temporal evolution of the plume can be revealed FLEXPART evaluated by several tracer experiments (CAPTEX, ANATEX, ETEX)

Summary of workpackage Trajectory matching technique allows Faciliting the interpratation of satellite observations Attribution of SO2 to particular volcano/source Estimation of plume height Estimation of effective emission height Forecasting of plume motion Enhancement of Air Mass Factor derivation Together with sb and gb measurements, LPDM allows to complement the temporal and spatial development of an eruption Supplement and improvement of SACS monitoring and warning system

Atmospheric Monitoring of Volcanic Activity from Space MODIS: July 24th 2001

SO2 Outgassing Grimsvötn SO2 SCIAMACHY + AVHRR Nov 2, 2004

Envisaged tasks for Exupéry WP2 Basis: 1. SO2 Retrieval: Thomas, Erbertseder et al., 2005, J. Atm Chem 2. GOME-2 new sensor with daily global coverage at high spatial and spectral res Tasks: Application of scientific retrieval to GOME-2 Improvements for operational NRT processing Studies of sensitivity Estimation of mass Validation with ground-based measurements  advanced volcanic activity monitoring Forecasting of SO2 plumes  early warning for air traffic control

EUMETSAT Meteorological Satellite Conference Monitoring volcanic activity from space: Retrieval of sulphur dioxide plumes from ERS-2/GOME backscatter data EUMETSAT Meteorological Satellite Conference September 23rd 2005 Dubrovnik, Croatia W. Thomas, T. Erbertseder, T. Ruppert, M. van Roozendael, D. Balis, C. Meleti, C. Zerefos

Etna from space (III) Mt. Etna (Sicily) - July 2001 MODIS: July 24th 2001 ATSR-2: July 24th 2001

Retrieval of sulphur dioxide Air Mass Factors AMFs describe the enhancement of absorption along slant paths in the atmosphere. AMFs are pure radiative transfer simulations and are a function of Viewing geometry (SZA, LOS, AZM)  T-p- profiles, profile shape  trace gas concentration profiles, profile shape  Aerosol loading and aerosol optical properties  Albedo and height of the underlying reflecting surface  (ground or cloud-top)

Expectations for GOME-2/MeTop Improvements and drawbacks Drawbacks Improvements Higher spatial resolution – basic assumptions about homogeneity of pixels may break down Larger swath width demands more sophisticated radiative transfer modeling Higher sensitivity with respect to aerosol loading, i.e. we need a better a priori information about aerosol Higher spatial resolution – results much more representative for GOME-2 pixels Better temporal sampling  improved global monitoring Lessons learnt from GOME, ongoing algorithm development

Expectations for GOME-2/MeTop SCIAMACHY – MODIS versus GOME : 29th October 2002

Etna from space (I) Mt. Etna (Sicily) - July 2001 ISS: July 22nd 2001 http://earth.esa.int/ew/volcanoes/etna_it_01/

Etna from space (II) Mt. Etna (Sicily) - July 2001 LANDSAT: July 21st 2001 ASTER: July 29th 2001

Combining an Imager with GOME MODIS and GOME: July 24th 2001 three days SO2 composite image merging GOME data from 22nd to 24th July 2001

Retrieval of sulphur dioxide Slant column fitting – DOAS fit (NLLS) between 315 – 327 nm Ozone optical density by a factor of 100 higher than corresponding SO2 optical density Ozone absorption must be well-known to retrieve the weak SO2 absorption structures

Results Results Oct/Nov 2002 - trajectory analysis and vertical columns

GOME measurements Characteristics GOME scanning spectrometer 240 – 790 nm, λ  0.2 – 0.4 nm Nadir looking - across track scanning scan swath : 30.976° descending node used Sun-synchronous polar orbit (z = 785 km) Equ. crossing time: 10:30h Orbit duration: 100 minutes Inst. FOV: 2.9° x 0.14° pixel size: 320 x 40 km2 Global coverage in 3 days GOME scanning spectrometer Courtesy of Univ. Heidelberg, Germany

Retrieval of sulphur dioxide The problem: We measure the slant column but we need the vertical column