Met Office VAAC — features and benefits
The International Civil Aviation Authority (ICAO) has authorised the Met Office as the Volcanic Ash Advisory Centre (VAAC) with responsibility for monitoring and forecasting the movement of volcanic ash over the United Kingdom, Iceland and the north-eastern part of the North Atlantic Ocean.
We provide forecasts to the standards and tolerances set by the Regulator. Our model can be configured to provide forecasts to any tolerance of ash that is deemed safe by the aviation regulatory authorities.
The Met Office dispersion model
The Met Office Volcanic Ash Advisory Centre (VAAC) produces ash cloud dispersion forecasts by tracking model particles through the atmosphere, based on one of the world's best atmospheric modelling capabilities. It has a highly successful track record - including the 1991 Kuwaiti oil fires (First Gulf War); the 2005 Buncefield oil depot accident and the 2008 Bluetongue outbreak in northern Europe.
- Ash particles are moved by the three-dimensional forecast winds from the Met Office global weather model, which is among the most accurate weather forecasting models in the world.
- Ash is retained in the Met Office dispersion model until it is removed by physical processes including: fall-out due to gravity; settling on the surface, and washout - where the pollutant is 'swept out' by rain or snow and ash can be absorbed directly into cloud droplets.
- Our dispersion model predicts both the trajectory of the newly emitted ash and residual ash already in the atmosphere. This is important as we know that ash stays in the atmosphere for many days. For example, ash which is at least four days old it is clearly visible on the satellite imagery.
- The dispersion model has one of the most advanced particle size distribution of any dispersion model, allowing it to more accurately predict ash movement, removal and retention.
- Model forecasts are routinely validated and verified against all available observations, such as from satellite, radar, lidar and research aircraft. Throughout this incident the predictions of the ash cloud have verified and validated well against observations.
The Met Office VAAC consists of a team of highly trained and experienced weather forecasters and atmospheric dispersion scientists. Our dispersion model has been endorsed by the international meteorological community who recognise the benefits of using it.
- The model can be configured to provide forecasts to any tolerance of ash that is deemed safe by the aviation regulatory authorities.
- It gives a sound representation of where ash is likely to be present, because it uses world-leading weather data; only removes ash through physical processes, and represents the volcano in a realistic way.
- The dispersion model is routinely updated to represent the latest emission information on the volcanic eruption from the Icelandic Meteorological Office and the British Geological Society, including plume height and emissions rates. Met Office experts are in Iceland providing the latest information to our dispersion scientists.
- It represents the continuously erupting nature of the volcano. Some other models do not use a continuous eruption and each time the model is started it loses all memory of ash which was previously in the atmosphere. The Met Office dispersion model is the most appropriate for this type of volcanic eruption.
- The Met Office VAAC maintains ash, even when it is hidden by cloud on satellite imagery. The meteorology of Northern Europe means that cloud is prevalent and this is exacerbated because the volcano is erupting through a glacier and can, itself, result in cloud formation. The Met Office model is, therefore, the most appropriate for this type of volcanic eruption in this situation.
Last updated: 22 January 2013