08/2003 1

Volcanic Ash Detection and Prediction at the Met Office

Helen Champion, Sarah WatkinDerrick Ryall

Responsibilities

Tools

Etna 2002

Future

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Met Office is the London VAAC

VAAC = Volcanic Ash Advisory Centre

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28 October 2002 1316 UTC

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

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AVHRR London VAAC (ch4 -ch5)

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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

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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

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Additional Volcanic Ash graphics

Contoured plumes

Six levels

Easier comparisons with imagery / observations

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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

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Volcanic Ash - Trajectories

Also provide trajectories

Follow mean wind

Start at several levels

Quick indication of plume spread at various levels

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IcelandDaily 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

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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

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Etna 28/10/2002

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Etna 29/10/2002

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Etna 30/10/2002

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Etna 31/10/2002

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Etna 29/10/2002

Coloured by height(yellow=low level, red = high level)

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Effect of poorly resolved volcano

Inversion below summit

Plume remains in free troposphere

Peak not resolved

Inversion above ‘model’ summit

Plume also in boundary layer

Inversion

ActualModel

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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

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Release surface to FL200 Release FL100 to FL200

Impact of poorly resolved orography

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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)

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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