Applying Mass Eruption Rates in an Operational Dispersion Model

Transcription

1 Applying Mass Eruption Rates in an Operational Dispersion Model Frances Beckett, ADAQ, Met Office MeMoVolc Workshop, University of Iceland, May 2016

2 The London Volcanic Ash Advisory Centre (VAAC) The Met Office is the home of the London VAAC Volcanic Ash Graphics Supplementary Ash Concentration Plots

3 NAME NAME is a Lagrangian atmospheric dispersion model Developed and maintained by the ADAQ research group at the Met Office Wide range of applications from Animal Diseases to Volcanic Ash. Wide range of users: Academic institutions e.g. University of Bristol, University of Geneva Other Met Offices e.g. Icelandic Met Office and BOM Australia...and of course it used by the London VAAC!

4 How is NAME used by the London VAAC? In order to run NAME to forecast the dispersion of the ash cloud we need to know: Location of the eruption vent Timings The plume height The source strength The mass fraction of fine ash The particle size distribution We assume the particles are spherical and have a fixed density of 2300 kg m -3

5 Key Sources of Information Official: Icelandic Met Office by telephone Icelandic Met Office status reports Secondary: British Geological Survey Nordic Volcanological Centre, University of Iceland Satellite Applications Links to academia

6 Volcanic Ash Status Reports Volcano Time Height

7 Key Sources of Information Official: Icelandic Met Office by telephone Icelandic Met Office status reports Secondary: British Geological Survey Nordic Volcanological Centre, University of Iceland Satellite Applications Links to academia

8 Applying a Mass Eruption Rate (MER) The VAAC system uses the Mastin Relationship to determine the total MER from the eruption plume height above summit But! For long-range transport we are only interested in the ash in the distal plume Our default assumption is 5% of the mass remains in the distal plume. Ideally we would also know the particle size distribution of this remaining ash. London VAAC Default PSD Mastin et al. (2009)

9 The VAAC Interface Plume Height, Timing and Mass Fraction

10 Forecasts are sensitive to the MER applied Total Column Mass Loadings Beckett et al. (2015) Operational Air Concentration Charts Mass Fraction 1.7 % 5 % 15 %

11 Producing the Forecast - Timings At the start of a new eruption a very rapid first forecast is required Forecasts are then issued every 6 hours at 00:00, 06:00, 12:00 and 18:00 UTC Each forecast is a 6 hour time average

12 Producing the Forecast Timings...what this means for source term data At the start of a new eruption a very rapid first forecast is required We need data very quickly on the order of hours Forecasts are then issued every 6 hours at 00:00, 06:00, 12:00 and 18:00 UTC Volcanic Ash Status Reports are disseminated every 3 hours We need to know the source of the data and the uncertainty Each forecast is a 6 hour time average We can represent changes in the plume height and MER within this period We need to know the validity time We can also modify the source term used to represent the past

13 The Forecast Process Met Office Weather forecast models Other models Satellite + Other Observations Weather observations Volcano Data NAME Forecaster Crown copyright Met Office VAAC Chart & other products

14 Summary Dispersion model forecasts are sensitive to the MER applied We need to know the total MER and the fraction on the fine ash (D < 100 µm) The default used by the London VAAC is 5% of the total MER calculated using the Mastin relationship The first forecast is produced within hours of an eruption A validity time and the associated uncertainty with the data must be provided Even if data can not be provided in near real time it is still useful to us! Acknowledgments: I wish to thank Claire Witham and ADAQ for their support and guidance. Andrew Jones produced the plots of operational air concentrations with varying mass fractions. References: Beckett et al. (2015) Sensitivity of dispersion model forecasts of volcanic ash clouds to the physical characteristics of the particles. JGR: 120 Mastin et al. (2009) A multidisciplinary effort to assign realistic source parameters to models of volcanic ash-cloud transport and dispersion during eruptions. JVGR:186.

15 Any Questions?