Ground-based radar remote sensing of explosive volcanic ash eruptions: Numerical models and quantitative applications

Microphysical and dynamical features of volcanic clouds, due to Plinian eruptions, can be quantitatively monitored by using ground-based microwave weather radars. In order to illustrate the potential of this microwave active remote sensing technique, the case study of the eruption of Augustine volcano in Alaska in January 2006 is described and analyzed. Volume data, acquired by a NEXRAD WSR-88D S-band ground-based weather radar, are processed to automatically classify and estimate eruptive cloud particles concentration. In this study we use the plume model ATHAM to investigate processes leading to particle aggregation in the eruption column. The interactions of hydrometeors and volcanic ash within the eruption column that lead to aggregate formation are simulated for the first time within a rising eruption column. A sensitivity analysis is carried out to evaluate the impact of aggregate particles on microwave radar reflectivity. The ash retrieval physical algorithm is based on the backscattering microphysical model of volcanic cloud particles, used within a Bayesian classification and optimal regression algorithm. The evolution of the Augustine eruption is discussed in terms of radar measurements and products, pointing out the unique features, the current limitations and future improvements of radar remote sensing of volcanic plumes.