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The flow inside a rotating annulus tilted with respect to gravity is characterized experimentally and theoretically. As in the case of a tilted rotating cylinder the flow is forced by the free surface, maintained flat by gravity. It leads to resonances of global inertial modes (Kelvin modes) when the height of fluid is a multiple of half the wavelength of the mode. The divergence of the mode is saturated by viscous effects at the resonance. The maximum amplitude scales as the Ekman number to the power -1/2 when surface Ekman pumping is dominant, and to the power -1 when volumic damping is dominant. An analytical prediction is given with no fitting parameter, in excellent agreement with experimental results. At lower Ekman numbers, the flow destabilizes with respect to a triadic resonance instability, as already observed by Xu & Harlander (Phys. Rev. Fluids, 2020). We provide here a linear stability analysis leading to the viscous threshold of the instability for small tilt angles. For large tilt angles, a centrifugal instability is observed due to the acceleration of the flow by the inner cylinder. Finally, the features of the turbulent flow and its mixing efficiency are characterized experimentally. We underline the potential interest of this configuration for bioreactors. [ABSTRACT FROM AUTHOR]

Accurate forecasting of volcanic particle (tephra) dispersal and fallout requires a reliable estimation of key Eruption Source Parameters (ESPs) such as the Mass Eruption Rate (QM). QM is usually estimated from the Top Plume Height (HTP) using empirical and analytical models. For the first time, we combine estimates of HTP and QM derived from the same sensor (radar) with mean wind velocity values (vW) for lava‐fountain fed tephra plumes associated with 32 paroxysms of Mt. Etna (Italy) to develop a new statistical model based on a Markov Chain Monte Carlo approach for model parameter estimation. This model is especially designed for application to radar data to quickly infer QM from observed HTP and vW, and estimate the associated uncertainty. It can be easily applied and adjusted to data retrieved by radars worldwide, improving our capacity to quickly estimate QM and related uncertainties required for the tephra dispersal hazard. Plain Language Summary: New radar‐based statistical model useful to quickly infer the mass eruption rate, usually the key parameter to initialize the tephra dispersion model, from the volcanic plume height during the eruptions. Key Points: X‐band radar observations of explosive eruptions can be used to estimate the eruption source parameters and associated uncertaintiesUsing the Markov Chain Monte Carlo model can be performed the statistical analysis of time seriesStatistical parametric model to infer the mass eruption rate from the measured top plume height [ABSTRACT FROM AUTHOR]

Explosive basaltic eruptions pose significant threats to local communities, regional infrastructures and international airspace. They produce tephra plumes that are often associated with a lava fountain, complicating their dynamics. Consequently, source parameters cannot be easily constrained using traditional formulations. Particularly, mass flow rates (MFRs) derived from height observations frequently differ from field deposit‐derived MFRs. Here, we investigate this discrepancy using a novel integral plume model that explicitly accounts for a lava fountain, which is represented as a hot, coarse‐grained inner plume co‐flowing with a finer‐grained outer plume. The new model shows that a plume associated with a lava fountain has higher variability in rise height than a standard plume for the same initial MFR depending on initial conditions. The initial grain‐size distribution and the relative size of the lava fountain compared to the surrounding plume are primary controls on the final plume height as they determine the strength of coupling between the two plumes. We apply the new model to the August 29, 2011 paroxysmal eruption of Mount Etna, Italy. The modeled MFR profile indicates that the field‐derived MFR does not correspond to that at the vent, but rather the MFR just above the lava fountain top. High fallout from the lava fountain results in much of the erupted solid material not reaching the top of the plume. This material deposits to form the proximal cone rather than dispersing in the atmosphere. With our novel model, discrepancies between the two types of observation‐derived MFR can be investigated and understood. Key Points: We have developed a new integral model that accounts for the coupling between a tephra plume and a lava fountainThe initial grain‐size distribution and radius of a lava fountain control the rise height of the surrounding tephra plumeThe model can explain the relationship between the tephra plume and cone deposits and the observed plume and lava fountain height [ABSTRACT FROM AUTHOR]

Abstract: Volcanic plumes from Etna volcano (Italy) are governed by easterly winds driving ash over the Ionian Sea. The limited land tephra deposit makes total grain‐size distribution (TGSD) assessment and its fine ash fraction highly uncertain. On 23 February 2013, a lava fountain produced a ~9‐km‐high column above sea level (a.s.l.). The atypical north‐easterly wind direction dispersed the tephra from Etna to the Puglia region (southern Italy) allowing sampling up to very distal areas. This study uses field measurements to estimate the field‐based TGSD. Very fine ash distribution (particle matter below 10 μm—PM10) is explored parameterizing the field‐TGSD through a bi‐lognormal and bi‐Weibull distribution. However, none of the two latter TGSDs allow simulating any far‐traveling airborne ash up to distal areas. Accounting for the airborne ash retrieved from satellite (Spinning Enhanced Visible and Infrared Imager), we proposed an empirical modification of the field‐based TGSD including very fine ash through a power law decay of the distribution. The input source parameters are inverted by comparing simulations against measurements. Results suggest a column height of ~8.7 km a.s.l., a total erupted mass of ~4.9 × 109 kg, a PM10 content between 0.4 and 1.3 wt%, and an aggregate fraction of ~2 wt% of the fine ash. Aerosol optical depth measurements from the AErosol RObotic NETwork are also used to corroborate the results at ~1,700 km from the source. Integrating numerical models with field, ground‐based, and satellite‐based data aims at providing a better TGSD estimation including very fine ash, crucial for air traffic safety. [ABSTRACT FROM AUTHOR]

In this paper we present a probabilistic hazard assessment for tephra fallout at Mt. Etna (Italy) associated with both short- and long-lived eruptions. Eruptive scenarios and eruption source parameters were defined based on the geological record, while an advection-diffusion-sedimentation model was used to capture the variation in wind speed and direction with time after calibration with the field data. Two different types of eruptions were considered in our analysis: eruptions associated with strong short-lived plumes and eruptions associated with weak long-lived plumes. Our probabilistic approach was based on one eruption scenario for both types and on an eruption range scenario for eruptions producing weak long-lived plumes. Due to the prevailing wind direction, the eastern flanks are the most affected by tephra deposition, with the 122 BC Plinian and 2002-2003 eruptions showing the highest impact both on infrastructures and agriculture. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a new statistical approach which provides tephra deposit load and ash concentration using PUFF, a Lagrangian model widely used to forecast volcanic ash dispersal during volcanic crisis. We perform a parametric study in order to analyze the influence of each input parameter on model outputs. For this test, we simulate two eruptive scenarios similar to the 2001 (Scenario 1) and 1998 (Scenario 2) Etna eruptions using high resolution weather data and a domain of 170×170km. Results show that for both scenarios, we are able to calculate the tephra deposit load and ash concentration but the use of millions of particles is required. Specifically, up to 33 and 220millions of particles were necessary to accurately predict the tephra deposit and ash concentration in air, respectively. This is approximately two orders of magnitude larger than the values typically considered running PUFF. The parametric study shows that the horizontal diffusion coefficient, the time step of the simulations, the topography and the standard deviation of the particle distribution greatly affect the model outputs. We also validate the model by best-fit procedures. Results show a good comparison between field data of the 2001 Etna eruption and PUFF simulations, being inside 5 and 1/5 times the observed data, comparable with results of Eulerian models. This work will allow to reliably outline the areas of contaminated airspace using PUFF or any other Lagrangian model in order to define the No Fly Zone and ensure the safety aviation operations as required after the Eyjafjallajökull eruption. [Copyright &y& Elsevier]

In this paper we describe the results of a project ongoing at the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The objective is to develop and implement a system for monitoring and forecasting volcanic plumes of Etna. Monitoring is based at present by multispectral infrared measurements from the Spin Enhanced Visible and Infrared Imager on board the Meteosat Second Generation geosynchronous satellite, visual and thermal cameras, and three radar disdrometers able to detect ash dispersal and fallout. Forecasting is performed by using automatic procedures for: i) downloading weather forecast data from meteorological mesoscale models; ii) running models of tephra dispersal, iii) plotting hazard maps of volcanic ash dispersal and deposition for certain scenarios and, iv) publishing the results on a web-site dedicated to the Italian Civil Protection. Simulations are based on eruptive scenarios obtained by analysing field data collected after the end of recent Etna eruptions. Forecasting is, hence, supported by plume observations carried out by the monitoring system. The system was tested on some explosive events occurred during 2006 and 2007 successfully. The potentiality use of monitoring and forecasting Etna volcanic plumes, in a way to prevent threats to aviation from volcanic ash, is finally discussed. [ABSTRACT FROM AUTHOR]

Abstract: We perform a parametric and comparative study on three different tephra dispersal models (FALL3D, HAZMAP, and TEPHRA) applied to two different scenarios expected for Etna volcano. These scenarios are similar to the recent 2002–03 and 1990 Etna eruptions and correspond, respectively, to a weak and to a strong plume eruption. For each model and scenario we perform a parametric study on several inputs in order to quantify how a variation on a given input parameter (i.e. an uncertainty on the model input) affects the results of the model. The study considers topographic effects, different description for the eruption column, column height influence, different fits for terminal velocities of particles, the effect of particle shape and, finally, the variation of the modal grain-size. Model differences are quantified by means of a normalized distance that indicates how close, in average, the results from two different simulations are. We also compare predictions from different models to determine under which circumstances the use of a more elaborated model is justified. Results from our parametric study show that output of the models can be strongly sensitive to the uncertainties and assumptions on input parameters, such as mainly mass eruption rate, column height, distribution of the mass along the column, bulk grain-size distribution. This highlights that, for optimal forecasts, is urgent to improve the description of these parameters and of some important physical processes like fragmentation and eruption column dynamics. Further, differences between models are often lower than those due to the uncertainties of input parameters, although they become more high in simulating weak plumes. Thus the choice of the model mainly depends on the kind of application such as the need to simulate the evolution of volcanic clouds in the atmosphere. Finally, the use of both a semi-analytical (HAZMAP) and a fully computational (FALL3D) model for inverting field data of the 2001 Etna eruption showed that the best-fit parameters are similar for both models, and are consistent with values obtained using independent techniques. [Copyright &y& Elsevier]

A lengthy period of eruptive activity from the summit craters of Mt. Etna started in January 2011. It culminated in early December 2015 with a spectacular sequence of intense eruptive events involving all four summit craters (Voragine, Bocca Nuova, New Southeast Crater, and Northeast Crater). The activity consisted of high eruption columns, Strombolian explosions, lava flows and widespread ash falls that repeatedly interfered with air traffic. The most powerful episode occurred on 3 December 2015 from the Voragine. After three further potent episodes from the Voragine, activity shifted to the New Southeast Crater on 6 December 2015, where Strombolian activity and lava flow emission lasted for two days and were fed by the most primitive magma of the study period. Activity once more shifted to the Northeast Crater, where ash emission and weak Strombolian activity took place for several days. Sporadic ash emissions from all craters continued until 18 December, when all activity ceased. Although resembling the summit eruptions of 1998–1999, which also involved all four summit craters, this multifaceted eruptive sequence occurred in an exceptionally short time window of less than three days, unprecedented in the recent activity of Mt. Etna. It also produced important morphostructural changes of the summit area with the coalescence of Voragine and Bocca Nuova in a single large crater, the “Central Crater”, reproducing the morphological setting of the summit cone before the formation of Bocca Nuova in 1968. The December 2015 volcanic crisis was followed closely by the staff of the Etna Observatory to monitor the on-going activity and forecast its evolution, in accordance with protocols agreed with the Italian Civil Protection Department. [ABSTRACT FROM AUTHOR]

Over the last twenty years Mount Etna has produced more than one hundred explosive events ranging from light ash emissions to violent sub-plinian eruptions. Significant hazards arise from tephra plumes which directly threaten air traffic, and generate fallout affecting surrounding towns and infrastructures. We describe the first radar system, named VOLDORAD 2B, fully integrated into a volcano instrumental network dedicated to the continuous near-source monitoring of tephra emissions from Etna's summit craters. This 23.5 cm wavelength pulsed Doppler radar is operated in collaboration between the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC) and the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) since 2009. Probed volumes inside the fixed, northward-pointing conical beam total about 1.5 km in length, covering the summit craters which produced all recent tephra plumes. The backscattered power, related to the amount of particles crossing the beam, and particle along-beam velocities are recorded every 0.23 s, providing a proxy for the tephra mass eruption rate. Radar raw data are transmitted in real-time to the volcano monitoring center of INGV-OE in Catania and are used to automatically release alerts at onset and end of eruptive events. Processed radar parameters are also made available from the VOLDORAD database online ( http://voldorad.opgc.fr/ ). In addition to eruptive crater discrimination by range gating, relative variations of eruption intensity can be tracked, including through overcast weather when other optical or infrared methods may fail to provide information. Short-lived dense ash emissions can be detected as illustrated for weak ash plumes from the Bocca Nuova and New South East craters in 2010. The comparison with thermal images suggests that the front mushroom of individual ash plumes holds the largest particles (coarse ash and small lapilli) and concentrations at least within the first hundred meters. For these short-lived ash plumes, the highest particle mass flux seems to occur typically within the first 10 s. We also analyze data from the first lava fountain generating an ash and lapilli plume on 12 January 2011 that initiated a series of 25 paroxysmal episodes of the New South East Crater until April 2012. We illustrate the pulsating behavior of the lava fountain and show that vertical velocities reached 250 m s − 1 (with brief peaks exceeding 300 m s − 1 ), leading to mean and maximum tephra fluxes (DRE) of 185 and 318 m 3 s − 1 (with peaks exceeding 380 m 3 s − 1 ) respectively, and a total volume of pyroclasts emitted during the lava fountain phase of 1.3 × 10 6 m 3 . Finally, we discuss capacities and limits of the instrument, along with future work aimed at providing source term inputs to tephra dispersal models in order to improve hazard assessment and risk mitigation at Etna. [ABSTRACT FROM AUTHOR]