Charts. VAAC Best Practice 5-8 May Crown copyright Met Office

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1 Volcanic Ash Contamination Charts VAAC Best Practice 5-8 May 2015

2 Background to proposal Replace current Volcanic ash concentration charts with Volcanic Ash contamination charts using a total ash-column based approach. Currently three contamination levels (low, medium and high) are referenced in the VACP: Area of Low Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations equal to or less than ³ 2x10 g/m³ (note that the base threshold of > 2x10-4 g/m³ is missing from the VACP but included in the EASA(2012) definition) Area of Medium Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations greater than ³ 2x10 g/m³ but less than ³ 4X10 g/m³ Area of High Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations equal to or greater than ³ 4x10 g/m³, or areas of contaminated airspace where no ash concentration guidance is available.

3 Ash concentration issues Quantitative definition of VA concentration levels not recognised by IAVW as best practice IVATF ( ) concluded that science was not mature enough to produce forecasts using ash concentration within acceptable levels of uncertainty Accurate measurement of ash concentration only possible using research aircraft e.g. MOCCA, SAFIRE.

4 Visible and Discernible Ash Since 2011, the WMO VASAG through IAVWOPSG has developed a common understanding of the hazard to aircraft and a common process to observe and forecast the hazard leading to new definitions of the ash hazard:- Visible Ash: Volcanic ash that can be observed by the human eye Discernible Ash: Volcanic ash detected by: defined impacts on/in aircraft; or by agreed in situ and /or remote-sensing techniques.

5 EUR experience For EUR region a single line denoting ash/no ash boundary is not viable. Recognised that a SRA approach using more than one contamination level is necessary Note current medium/high level concentration thresholds are too close together But, any change will require new evidence on engine tolerances

6 Dispersion model characteristics Used around the world but confidence in output varies due to:- Uncertain eruption source parameters Modelling capabilities, esp. Tropical convection Differences in model formulation Availability of observations to verify output

7 Satellite Imagery Now more widely available to the VAACs using improved multi-spectral techniques that measure total mass column loading Detection threshold 0.2 g/m² (+/-0.15 g/m²) in good conditions Assuming a uniform mixed cloud 1000m thick 0.2 g/m² equates to 2x10-4 g/m³ concentration 2g/m² = ³ 2x10 g/m³

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9 Proposed new definitions (1) Area of Low Contamination: Area of Low Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations greater than 2x10-4 g/m 3, but equal to or less than 2x10-3 g/m 3. Using model ash column loading output (0.2 g/m 2 as proxy for 2x10-4 g/m 3 ) verified, validated and amended against agreed sources of qualitative in-situ and remote sensing information & AIREPS (qualitative evidence of visible ash or impact as described in Doc 9974).

10 Proposed new definitions (2) Area of Medium Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations greater than 2x10-3 g/m 3, but less than 4x10-3 g/m 3. Using model ash column loading output (2 g/m 2 as proxy for 2x10-3 g/m 3 ) verified, validated and amended against available quantitative in-situ and remote sensing data.

11 Proposed new definitions (3) Area of High Contamination: An airspace of defined dimensions where volcanic ash may be encountered at concentrations equal to or greater than 4x10-3 g/m 3. Using model ash column loading output (4 g/m 2 as proxy for 4x10-3 g/m 3 ) verified, validated and amended against available quantitative in-situ and remote sensing data and a qualitative assessment of the contiguous eruptive plume.

12 Rationale for use of ash mass column loading During Ejya measured ash thickness ranged between a few 00 to 3000m. 1000m is a good average. Method makes maximum use of data from satellite allowing forecaster to make better informed judgements on extent of ash Availability of ash top data allows better constrained forecasts Thin layers (less than 1000m thick) may have higher concentrations but can be avoided by small climb or descent. LIDAR data will provide more data on ash bases

13 Case Studies Against charts and VAAs issued during 2010 and 2011 eruptions Depict generally reduced contamination areas and more accurately located areas after forecaster intervention.

14 Volcanic Ash T+0 annotated satellite image Issued 0945 UTC on Wed 21 Jan 2015 EXERCISE EXERCISE EXERCISE Low confidence: PIREP report of VA at 0930z, FL300-FL330, not consistent with satellite imagery High Confidence VA visible on imagery and consistent with reports from IMO

15 Annotated Satellite Image Issued every three hours by the VAAC during an eruptive event Shows all available evidence for existence, or not, of VA with confidence level (High/Low) Provides an ongoing commentary during an event for the position of VA Can be used, in real time, to verify the current VA forecast products (VAA/VAG, VACC).

16 Next steps Present to EUR/NAT VATF for consideration Update EUR/NAT VACP Potential implementation in late 2015 VACC charts would essentially look the same as now with L-M-H contours and ash base/top height Can be captured on single chart per timestep leading to significant reduction in number of charts

17 Possible format of Volcanic Ash Contamination Chart (VACC) Modelled VA Mass Column Loading Valid 1800 UTC 17/04/2015 This is a guidance product, supplemental to the official VAAC London Volcanic Ash Advisory and Volcanic Ash Graphic products. Issue time: SFC

18 Thank you