1. Volcanic Ash Detection and Prediction at the Met Office
Helen Champion, Sarah Watkin Derrick Ryall
Responsibilities
Tools
Etna 2002
Future

2. Met Office is the London VAAC
VAAC = Volcanic Ash Advisory Centre

3. Satellite ash detection products
AVHRR
ch4 (10.8 m) - ch5 (12.0 m)
available within 30 mins
Covers three areas:
Mediterranean area (Mt. Etna)
London VAAC
Iceland
Frequency
3 hourly over Iceland
6 hourly over the Mediterranean
28 October UTC

4. AVHRR London VAAC (ch4 -ch5)

5. Met Office NAME model Dispersion model
Predicts the transport of airborne pollutants
1-1000’s km, hours - days
Lagrangian particle model
Emergency response
nuclear, volcano, fire, FMD
Air pollution
episodes, forecasts, chemistry
Source attribution
where, when, how much
source/receptor relationships
CTBTO

6. Volcanic Ash Graphics Three levels FL350-FL550 FL200-FL350
Surface-FL200
Source
Unit release
between summit height and plume top
assumes particle size distribution
T+6,12,18,24
Extent of ‘visible’ ash cloud

7. Additional Volcanic Ash graphics
Contoured plumes
Six levels
Easier comparisons with imagery / observations

8. Recent Improvements to NAME
Automated plotting threshold for visual ash cloud concentrations
Previously manual forecaster input based on obs
Upgraded to use ‘New Dynamics’ version of Unified Model
3 hourly global fields to T+144, ~60km resolution
Increased vertical resolution (particularly near tropopause)
Revised boundary layer turbulence schemes

9. Volcanic Ash - Trajectories
Also provide trajectories
Follow mean wind
Start at several levels
Quick indication of plume spread at various levels

10. Iceland Daily runs Improve response times and preparedness
Daily simulations using NAME
Release from Katla
6 hour release
0, 6, 12 & 18Z
surface to FL400
Output on six levels

11. Etna eruption 2002 27 Oct 2002 Etna erupted to ~FL200
Emissions continued over several days
Useful case to look at
Full range of satellite imagery
Area largely cloud free
Use NAME to simulate first 10 days of emissions
Continuous release from surface to FL200
Compare concentrations (FL100 & FL200) with satellite imagery, particularly ch4-ch5

12. Etna 28/10/2002

13. Etna 29/10/2002

14. Etna 30/10/2002

15. Etna 31/10/2002

16. Etna 29/10/2002
Coloured by height (yellow=low level, red = high level)

17. Effect of poorly resolved volcano
Model
Actual
Inversion
Peak not resolved
Inversion above ‘model’ summit
Plume also in boundary layer
Inversion below summit
Plume remains in free troposphere

18. Poorly resolved orography
Particular problem with isolated peaks
No simple solution as NWP data will not properly represent flow around/over peak
If use ‘model’ summit height column is ‘stretched’ - material spreads over twice the height, giving lower concentrations
Suggest using ‘elevated’ source

19. Impact of poorly resolved orography
Release surface to FL200
Release FL100 to FL200

20. Future Work Volcanic ash detection
SEVERI on MSG (including AVHRR ch4-ch5)
15 minute imagery
Automatic detection system (Helen Watkin’s talk)
Upgrade to MSG
Operational implementation
Modelling
Need better definition of ‘Visual Ash Cloud’ - more appropriate would be ’concentrations hazardous to aviation’
Include sulphur as well as ash
Ensemble approach - multiple NAME runs on ECMWF EPS members (51)

21. Summary
Volcanic ash detection system and NAME predictions give increased confidence in operational VAAC results
Etna case study demonstrates the value of these tools
Issues for future work include
calibration of satellite imagery
representation of orography / height of release
definition of hazardous ash concentrations