1. 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

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

3. 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

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

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

6. 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 ?

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

8. 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)

9. 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

10. 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

11. 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

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

13. TMT 2: Backward Trajectories

14. TMT 3: Iteration with FWD trajectories

15. 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

16. 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

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

18. 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)

19. Validation of GOME SO2 retrieval

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

21. 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

22. 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

23. 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

24. 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)

59. 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

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

61. SO2 Outgassing
Grimsvötn
SO2 SCIAMACHY + AVHRR Nov 2, 2004

63. 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

64. 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

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

66. 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)

67. 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

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

69. Etna from space (I) Mt. Etna (Sicily) - July 2001 ISS: July 22nd 2001

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

71. 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

72. 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

73. Results
Results Oct/Nov trajectory analysis and vertical columns

74. GOME measurements Characteristics GOME scanning spectrometer
240 – 790 nm, λ  0.2 – 0.4 nm
Nadir looking - across track scanning
scan swath : °
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

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