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

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

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 2002 1316 UTC

AVHRR London VAAC (ch4 -ch5)

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

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

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

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

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

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

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

Etna 28/10/2002

Etna 29/10/2002

Etna 30/10/2002

Etna 31/10/2002

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

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

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

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

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)

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