Velocity profiles inside volcanic clouds from three‐dimensional scanning microwave dual‐polarization Doppler radars

Abstract

In this work, velocity profiles within a volcanic tephra cloud obtained by dual‐polarization Doppler radar acquisitions with three‐dimensional (3‐D) mechanical scanning capability are analyzed. A method for segmenting the radar volumes into three velocity regimes: vertical updraft, vertical fallout, and horizontal wind advection within a volcanic tephra cloud using dual‐polarization Doppler radar moments is proposed. The horizontal and vertical velocity components within the regimes are retrieved using a novel procedure that makes assumptions concerning the characteristics of the winds inside these regimes. The vertical velocities retrieved are combined with 1‐D simulations to derive additional parameters including particle fallout, mass flux, and particle sizes. The explosive event occurred on 23 November 2013 at the Mount Etna volcano (Sicily, Italy), is considered a demonstrative case in which to analyze the radar Doppler signal inside the tephra column. The X‐band radar (3 cm wavelength) in the Catania, Italy, airport observed the 3‐D scenes of the Etna tephra cloud ~32 km from the volcano vent every 10 min. From the radar‐derived vertical velocity profiles of updraft, particle fallout, and horizontal transportation, an exit velocity of 150 m/s, mass flux rate of 1.37 • 107 kg/s, particle fallout velocity of 18 m/s, and diameters of precipitating tephra particles equal to 0.8 cm are estimated on average. These numbers are shown to be consistent with theoretical 1‐D simulations of plume dynamics and local reports at the ground, respectively. A thickness of 3 ± 0.36 km for the downwind ash cloud is also inferred by differentiating the radar‐derived cloud top and the height of transition between the convective and buoyancy regions, the latter being inferred by the estimated vertical updraft velocity profile. The unique nature of the case study as well as the novelty of the segmentation and retrieval methods presented potentially give new insights into the analysis of volcanic cloud dynamics.

Paroxysmal Explosions, Lava Fountains and Ash Plumes at Etna Volcano: Eruptive Processes and Hazard Implications

“…There was another eruptive pause between April and the end of October 2013, followed by six additional paroxysmal explosive events until the end of that year. This last and third phase was very different from the previous, and comprised the most explosive end-member of the series, occurring on 23 November 2013 (Bonaccorso et al, 2014;Andronico et al, 2015;Carbone et al, 2015;Corradini et al, 2016;Montopoli, 2016). This very short but violent paroxysm produced an exceptionally high LF of over 2.5 km above the crater, and was the only one at the NSEC that did not produce lava flows (Bonaccorso et al, 2014).…”

Mass Eruption Rates of Tephra Plumes During the 2011–2015 Lava Fountain Paroxysms at Mt. Etna From Doppler Radar Retrievals

“…Marzano et al (2006) produced a procedure to retrieve ash mass load parameters (i.e., VARR model) using an electromagnetic scattering model and Dual-polarization radar observables. Their work was applied to Etna paroxysmal activity in 2013 (Corradini et al, 2016;Montopoli, 2016) and in December 2015 (Vulpiani et al, 2016) using the volume information of the X-Band (3 cm wavelength) weather radar located at Catania airport (30 km south from the Etna's summit), with a 3-D scan time resolution of 10 min.…”

Reconstructing volcanic plume evolution integrating satellite and ground-based data: application to the 23 November 2013 Etna eruption

“…We applied this methodology to the 23 November 2013 Etna paroxysm, which occurred from the New South-East Crater (hereinafter NSEC), being the most active crater in the last 20 years (Behncke et al, 2014;De Beni et al, 2015). Atypical winds dispersed the plume north-eastwards, driving the tephra towards the Calabria and Apulia regions (∼ 400 km from the source), where ash fallout was reported (Bonaccorso et al, 2014;Andronico et al, 2015;Montopoli, 2016). A few hours after the eruption, tephra was sampled along the plume axis from Etna (i.e.…”

“…The Moderate Resolution Imaging Spectro-radiometer (MODIS) aboard the NASA-Aqua polarorbit satellite was also used to describe the eruption features (Corradini et al, 2016). On the other hand, concerning ground-based instruments, the X-Radar (Montopoli, 2016; and the visible/thermal cameras (Corradini et al, 2016) provided time-series data of the plume height and the erupted mass.…”

“…To furnish the ESPs required by the FALL3D tephra dispersal model, we used the FPlume integral plume model describing the eruptive column based on the buoyant plume theory (Morton et al, 1956). FPlume solves a set of 1-D cross-section-averaged equations for mass, momentum, and energy conservation in the eruption column, accounting for wind coupling, air moisture, particle re-entrainment, and ash aggregation effects .…”