Terminal settling velocity measurements of volcanic ash during the 2002–2003 Etna eruption by an X‐band microwave rain gauge disdrometer

Abstract

[1] This is the first report in the scientific literature of direct measurement of the terminal settling velocity of volcanic particles during an eruption. Field measurements using a continuous wave X-band disdrometer were carried out at Mt. Etna on 18 and 19 December 2002, when the explosive activity produced a 4 km high volcanic plume. These data allow the estimation of the intensity of the fallout and the measurement of the terminal settling velocities of the volcanic particles in real-time. The main results are: (1) the tested instrument detected coherent falling volcanic particles from 0.2 to 1 mm diameter; (2) measured terminal settling velocities were in agreement with both experimental and theoretical methods; (3) however, the measured velocities were clustered around few discrete values, rather than a range of velocities as would be expected if the particles were falling simultaneously and discretely. This new methodology has many new applications for local hazard mitigation and improved understanding of fallout processes.

Characterization of shape and terminal velocity of tephra particles erupted during the 2002 eruption of Etna volcano, Italy

“…The instrument is an X-band continuous wave radar and is based on the Doppler shift induced by falling particles on the transmitted electromagnetic wave (Prodi et al 2000). The radar detected the terminal settling velocities of the falling particles (Scollo et al 2005), and their values were in the same range as those measured experimentally (Wilson and Huang 1979) and calculated analytically (Kunii and Levenspiel 1969) for spherical particles with similar dimension and density. Nevertheless, during the two field tests, only four distinct velocity peaks were observed that could be related to aggregation into preferential aerodynamic diameters or caused by settling-driven instabilities (Scollo et al 2005).…”

“…During the 2002-2003 Etna eruption, a new instrument, originally designed as a rain gauge disdrometer, was used to investigate the terminal settling velocity of volcanic particles (Scollo et al 2005). The instrument is an X-band continuous wave radar and is based on the Doppler shift induced by falling particles on the transmitted electromagnetic wave (Prodi et al 2000).…”

“…Volcanic ash analyzed in this paper was collected on 18 December 2002 at Piano del Vescovo about 5 km from the volcanic vent (Scollo et al 2005). During that day, the intensity of the eruption remained at medium-high levels producing the eruptive column about 4000 m a.s.l., and the volcanic clouds flowed forward S-SE.…”

Monitoring and forecasting Etna volcanic plumes

“…The sensor is a low power (10 mW) Continuous Wave (CW) Doppler radar operating at a frequency of 9.5 GHz (Prodi et al, 2000). PLUDIX was tested for the first time during 2002-2003 Etna eruption and was able to measure terminal settling velocity of volcanic particles falling above the radar (Scollo et al, 2005). The instrument was considered as a helpful tool for the real-time monitoring because it can evaluate the particle fall rate and eventually the total grain-size distribution using inverse modelling.…”

Volcanological Applications of Doppler Radars: A Review and Examples from a Transportable Pulse Radar in L-Band

“…A compact X-band continuous wave, low power (10 mW) Doppler Radar (PLUDIX, 9.5 GHz frequency of operation), originally designed as a rain gauge disdrometer, was utilized to measure the terminal settling velocities and infer sizes of plume fallout at Mount Etna in 2002 (Scollo et al, 2005) and Eyjafjallajökull in 2010 (Bonadonna et al, 2011). PLUDIXderived particle size distributions agree reasonably well with sieve-derived grain size distributions, but only for diameter range above 500 microns, and so should be used within a few kilometers from the source.…”