High-Resolution Volcanic Ash Dispersal Forecast

Operational volcanic ash dispersal forecasts are routinely used to prevent aircraft encounters with volcanic ash clouds and to perform re-routings avoiding contaminated airspace areas. However, a gap exists between current operational forecast products (e.g. issued by the Volcanic Ash Advisory Centers) and the requirements of the aviation sector and related stakeholders. Two aspects are particularly critical: 1) time and space scales of current forecasts are coarse (for example, the current operational setup of the London VAAC at U.K. Met. Office outputs on a 40 km horizontal resolution grid and 6 hour time averages) and; 2) quantitative forecasts. Several studies (e.g. Kristiansen et al., 2012) have concluded that the main source of epistemic/aleatory uncertainty in ash dispersal forecasts comes from the quantification of the source term (eruption column height and strength) which, very often, is not fully-constrained on real time. This limitation can be circumvented in part by integrating into models ash cloud observations away from the source, typically from satellite retrievals of fine ash column mass load (i.e. vertical integration of concentration). Model data assimilation has the potential to improve ash dispersal forecasts by an efficient joint estimation of the (uncertain) volcanic source parameters and the state of the ash cloud.