When a volcano in its area of responsibility erupts, the London Volcanic Ash Advisory Centre (VAAC), based at the Met Office, runs the NAME atmospheric dispersion model.
This, and similar models, are well proven and we can use them to predict the spread of pollutants following a chemical or nuclear leak or even the spread of airborne diseases. In this case we use the dispersion model to forecast the spread of volcanic ash plumes.
The London VAAC forecaster provides the location, start time, release height and the top and bottom of the plume (if known) and the model is run. It takes about 15 minutes to complete.
Output from this model is in a map-based graphical format, and can detail expected ash concentrations over a large region. The forecaster uses this detail to prepare the volcanic ash advisory message with the expected positions of the ash plume for up to 24 hours ahead.
The Advisory message is then used by aviation authorities to decide whether airspace needs to be closed to prevent aircraft encountering volcanic ash.
The graphic below shows an example of the output from the NAME model based on an eruption of the Mount Stromboli in Italy. (Stromboli is not in the London VAAC area.)
NAME example output
The Met Office has developed two products for the London VAAC that use satellite data to detect and track volcanic ash clouds.