Abstract
Abstract. Volcanic ash modeling systems are used to simulate the atmospheric dispersion of volcanic ash and to generate forecasts that quantify the impacts from volcanic eruptions on infrastructures, air quality, aviation, and climate. The efficiency of response and mitigation actions is directly associated with the accuracy of the volcanic ash cloud detection and modeling systems. Operational forecasts build on offline coupled modeling systems in which meteorological variables are updated at the specified coupling intervals. Despite the concerns from other communities regarding the accuracy of this strategy, the quantification of the systematic errors and shortcomings associated with the offline modeling systems has received no attention. This paper employs the NMMB-MONARCH-ASH model to quantify these errors by employing different quantitative and categorical evaluation scores. The skills of the offline coupling strategy are compared against those from an online forecast considered to be the best estimate of the true outcome. Case studies are considered for a synthetic eruption with constant eruption source parameters and for two historical events, which suitably illustrate the severe aviation disruptive effects of European (2010 Eyjafjallajökull) and South American (2011 Cordón Caulle) volcanic eruptions. Evaluation scores indicate that systematic errors due to the offline modeling are of the same order of magnitude as those associated with the source term uncertainties. In particular, traditional offline forecasts employed in operational model setups can result in significant uncertainties, failing to reproduce, in the worst cases, up to 45–70 % of the ash cloud of an online forecast. These inconsistencies are anticipated to be even more relevant in scenarios in which the meteorological conditions change rapidly in time. The outcome of this paper encourages operational groups responsible for real-time advisories for aviation to consider employing computationally efficient online dispersal models.
Highlights
Volcanic ash modeling systems are used to simulate the atmospheric dispersion of volcanic ash and to generate operational short-term forecasts to support civil aviation and emergency management
We evaluate the skills of the offline versus online NMMB-MONARCH-ASH forecasts in terms of their ash column loading (ACL) using different quantitative and categorical evaluation scores
This paper quantifies the systematic errors inherent in offline coupling strategies employed for operational volcanic ash forecasting
Summary
Volcanic ash modeling systems are used to simulate the atmospheric dispersion of volcanic ash and to generate operational short-term forecasts to support civil aviation and emergency management. In the event of an eruption, the individual Volcanic Ash Advisory Center (VAAC) responsible for the affected region combines ash cloud satellite observations and dispersal simulations to issue periodic volcanic ash advisories (VAAs) These are text and graphical products informing on the extent of the ash clouds at relevant flight levels and their forecasted trajectories at 6, 12, and 18 h ahead that are updated periodically or whenever significant changes occur in the eruption source term. All this information is used to ensure flight safety by supporting critical decisions such as closure of ash-contaminated air space and airports or diversion of aircraft flight paths to prevent encounters. The noteworthy economic impact and social disruption of these air traffic restrictions are, directly associated with the accuracy of the volcanic ash cloud detection and modeling systems
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