© crown copyright met office presentation delivered with expert commentary. please check against...

© Crown copyright Met Office PRESENTATION DELIVERED WITH EXPERT COMMENTARY. PLEASE CHECK AGAINST DELIVERY

Modelling and Forecasting of the Eyjafjallajökull eruptionAnton Muscat

Met Office

© Crown copyright Met Office

Order of presentation:

• UK Met Office and London VAAC

• Creating a weather forecast

• NAME – the Met Office’s dispersion model

• Responsibilities of a VAAC

• Volcanic eruption – typical timeline

• Using observations to verify NAME

• Conclusions


Met Office and London VAAC

• Met Office provides weather and climate services to UK Government, General Public and commercial customers.

• Many of the forecasts are produced from the forecasting Operations Centre at Exeter.

• London VAAC (Volcanic Ash Advisory Centre) is actually based in the Operations Centre at Exeter and is part of a forecasting team who provide advice on many different aspects of atmospheric dispersion (nuclear accidents, chemical release, biological release, etc.)


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Creating the weather forecast

Forecast Model

Observations

Application of classical laboratory physics to the thin shell of turbulent gases that is our

atmosphere


From weather forecast to predicting plume movement

• Weather forecast will provide us with details of how air is moving within the atmosphere

• Apply this weather forecast (wind and other information) to a dedicated Dispersion Model

• Met Office have a dispersion model called NAME (Numerical Atmospheric dispersion Modelling Environment III)

• NAME was developed following the Chernobyl accident in 1986 and is a world-leading dispersion model.


Applications of NAME

• Nuclear and chemical releases

• Volcanic ash

• Disease spread (foot and mouth, blue tongue disease, legionaires disease)

• Major fires

• Emergency planning – ‘what if’ scenarios


Dispersion modelling

Volcano

Wind transports the ash

Random wind variations spread ash into a broad plume

Gravity causes ash to fall through the atmosphere

Rain washes ash on to the ground


VAAC - Volcanic Ash Advisory Centres

• 9 VAACs implemented by ICAO in 1987


London VAAC

• The VAAC London procedures are set up to ensure absolute reliability in a safety critical situation

• VAAC London is staffed 24x7 with forecasters trained to identify ash in satellite imagery, to operate the NAME dispersion model, and to generate the standard advisory charts

• Once an event is in progress, expert scientists are on call to support the 24x7 operation


Role of VAACs

• International Civil Aviation Organisation (ICAO) recommends VAACs should provide guidance on presence of “any ash” in the atmosphere (London VAAC uses > 2x10-4 g/m3)

• Production of advisories detailing the spatial dispersion of VA

• Running (and/or utilisation of output from) NWP dispersion models

• Monitoring of observational data, especially satellite imagery for the presence of VA

• VAAC advisories and graphics are produced out to 24 hours for use by state Met Watch Office (MWO)

• MWO produce VA SIGMETs based on VA Advisories


Standard VAAC Graphic


Moving from ash presence to ash concentration• Original international VAAC guidance of no-ash

zone based on empirical evidence of the edge of plume.

• Estimated volcano release rates for Eyjafjallajökull indicated that no-ash limit equated to peak concentrations of 200 micrograms/m3 (red zone), corroborated by observations.

• Consultation based on safe engine ingestion rates indicated that concentrations 10 times higher could be hazardous. Black zone introduced to indicate peak concentrations of 2000 micrograms/m3 and higher.


Supplementary London VAAC Products

• During the event CAA asked London VAAC to provide supplementary products to standard service

• Red and black charts

• Red and black charts with black buffer zone

• Red, grey and black charts

• CSV files for red, grey and black thresholds

• 3 hourly update charts

• 5,000ft layer charts

• 5 day red, grey and black charts

• London VAAC has no influence on these thresholds. They are stipulated by CAA on advice from engine manufacturers


Supplementary Red, Grey and Black Chart


Volcanic eruption – a typical timeline• UK Met Office has close links with Iceland Met Office

(IMO) – VA exercises every 3 months.

• In the event of increased seismic activity on (or near) Iceland, IMO contact Met Office to inform.

• The moment an eruption occurs (or is thought likely to occur soon) IMO contact Met Office

• Assuming that an eruption has started, NAME is run with the supplied details (height of plume, etc.)

• Typically, VAG/VAA guidance is issued approx. 60-90 minutes after eruption starts.

• VAG/VAA guidance then updated regularly thereafter, AT LEAST every 6 hours.

• London VAAC forecasters take part in regular teleconferences with Eurocontrol/NATS, as well as liaising with VAAC Toulouse and VAAC Montreal.


Techniques for observing Volcanic Ash

• Satellite imagery

• LIDAR (Light Detection and Ranging)

• Sampling of atmosphere by suitably equipped aircraft.

• Reports from aircraft when they encounter ash.

• Reports of ash depositing on the ground


Satellite imagery

• Okay in certain circumstances (newly erupted ash, clear skies) but increasingly difficult to see ash after approx. 24 hours in the atmosphere, and impossible to detect when cloud overlays the ash.

• Animations of satellite imagery, over a period of time, are the best way to observe ash via satellite imagery.


Comparison with NAME1200 UTC 10/05/2010

Edge of ‘visible’ plume on satellite retrievals

Comparison with other models: 1200z on 10 May

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Light Detection and Ranging (LIDAR)

• Emits a pulse of laser light and detects backscatter signal

• Detects the altitude and thickness of aerosol layers

• When collocated with other technology is possible to estimate the total aerosol content of the atmosphere and mass concentration

• Only available in a limited number of fixed locations.


LIDAR locations in the UK

Lidarlocations

Reading

Lidarlocations

Reading


Suitably equipped aircraft

• Provides high-quality data

• Often not in real-time – data can be many hours old before it is viewable by forecasters

• Expensive to operate

• Limited coverage


Other observations

• During the ash event, many ad-hoc observations of volcanic ash were received

• Some could be verified, some could not

• London VAAC considered these observations when compiling the VAG/VAA products

• Changes were made to the computer model output if evidence from Satellite/LIDAR/Observations warranted it.


Concluding remarks

• On vast majority of occasions, NAME successfully captured horizontal extent of the ash plume and the variations within it, including indications of peak concentrations.

• As with all models, concentrations are determined by the characteristics of the volcanic emission – mass, particle size and height – which are hugely uncertain.

• Recognize a need for a consistent approach by all VAACs to forecasting VA – this is currently being taken forward.

© crown copyright met office presentation delivered with expert commentary. please check against...

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