Near Real-Time Detection of Tephra Eruption Onset by using Weather Radar: case studies of Grimsvotn and Etna eruptions

During an eruptive event the near real-time monitoring of volcanic explosion onset is a key factor to predict ash plume dispersion and to mitigate risk to air traffic. Microwave weather radars have proved to be a fundamental instrument to derive eruptive source parameters and in this work we extend this capability to include an early- warning detection scheme within the overall Volcanic Ash Radar Retrieval methodology. This scheme, called volcanic ash detection (VAD) algorithm, is based on a hybrid technique using both fuzzy logic and conditional probability giving as outputs the Probability of Ash Eruption onset (PAE) and the Spatial Identification Map. The PAE behavior, over time, is an indicator of eruption column ejecting tephra in the surrounding of the volcanic vent, on the other hand, in the Spatial Identification Map the discrimination between volcanic and meteorological targets is performed in any pixel of radar domain. Examples of VAD applications are shown for two case studies, including the Icelandic Grímsvötn eruption in 2011 and the Italian Mt. Etna volcano eruption in 2013. Estimates of the eruption onset from the radar-based VAD module are compared with infrasonic array data. Results confirm in both cases the potential of microwave weather radar for ash plume monitoring in near real-time and its complementarily with infrasonic array for early-warning system design