Flow visualization and analytical study on the exhaust gas diffusion of a frigate

Wind tunnel flow visualization tests were conducted to analyse the efflux velocity impacts and the yaw angle on the smoke dispersion of the exhaust for a generic frigate. An analytical study was also implemented to obtain the exhaust plume trajectories. The 1/100 scale generic frigate, having a platform for helicopters on the aft of the ship, was built and employed during the experimental study. The forward and astern cruises of the frigate were considered. It is found that the plume height and the exhaust gases momentum increase with the velocity ratio. The problem of smoke nuisance was observed for the ratios with low velocity such as K=0.2. The plume was also directed towards the helicopter platform when the yaw angles are higher than 10°. The experimental results are compared with the analytical solutions for three different velocity ratios. The compliance between the experimental and analytical results is found to be consistent.

Classifying Major Explosions and Paroxysms at Stromboli Volcano (Italy) from Space

Stromboli volcano has a persistent activity that is almost exclusively explosive. Predominated by low intensity events, this activity is occasionally interspersed with more powerful episodes, known as major explosions and paroxysms, which represent the main hazards for the inhabitants of the island. Here, we propose a machine learning approach to distinguish between paroxysms and major explosions by using satellite-derived measurements. We investigated the high energy explosive events occurring in the period January 2018–April 2021. Three distinguishing features are taken into account, namely (i) the temporal variations of surface temperature over the summit area, (ii) the magnitude of the explosive volcanic deposits emplaced during each explosion, and (iii) the height of the volcanic ash plume produced by the explosive events. We use optical satellite imagery to compute the land surface temperature (LST) and the ash plume height (PH). The magnitude of the explosive volcanic deposits (EVD) is estimated by using multi-temporal Synthetic Aperture Radar (SAR) intensity images. Once the input feature vectors were identified, we designed a k-means unsupervised classifier to group the explosive events at Stromboli volcano based on their similarities in two clusters: (1) paroxysms and (2) major explosions. The major explosions are identified by low/medium thermal content, i.e., LSTI around 1.4 °C, low plume height, i.e., PH around 420 m, and low production of explosive deposits, i.e., EVD around 2.5. The paroxysms are extreme events mainly characterized by medium/high thermal content, i.e., LSTI around 2.3 °C, medium/high plume height, i.e., PH around 3330 m, and high production of explosive deposits, i.e., EVD around 10.17. The centroids with coordinates (PH, EVD, LSTI) are: Cp (3330, 10.7, 2.3) for the paroxysms, and Cme (420, 2.5, 1.4) for the major explosions.

On the dynamics of stratified particle-laden plumes

An experimental study on stratified particle-laden plumes is presented and five steady-state flow regimes have been identified. The steady-state behaviour of the plume is directly related to the magnitude of the convective velocity associated with particle-induced instabilities, $U_c$ , in relation to the terminal settling velocity of each individual particle, $u_{st}$ . When $u_{st}>U_c$ , the ratio of particle to fluid buoyancy flux at the source, $P$ , becomes important. For $P<0.2$ , the plume dynamics appears very similar to a single-phase plume as particle recycling has minimal impact on the steady-state plume height. When $P>0.2$ , the plume height decreases significantly, creating an anvil-shaped intrusion similar to those associated with explosive volcanic eruptions. Importantly, the measured steady-state heights of plumes within this settling regime validate the collapse model of Apsley & Lane-Serff (J. Fluid Mech., vol. 865, 2019, pp. 904–927). When $u_{st}\leqslant U_c$ , particle re-entrainment behaviour changes significantly and the plume dynamics becomes independent of $P$ . When $u_{st}\approx U_c$ , a trough of fluid becomes present in the sedimenting veil due to a significant flux of descending particles at the edge of the plume. Once $u_{st}< U_c$ , the particles spreading in the intrusion become confined to a defined radius around the plume due to the significant ambient convection occurring beneath the current. For $u_{st}\ll U_c$ , or in the case of these experiments, when $U_c\geqslant 1\ \text{cm s}^{-1}$ , ambient convection becomes so strong that intrusion fluid is pulled down to the plume source, creating a flow reminiscent of a stratified fountain with secondary intrusions developing between the original current and the tank floor. Through an extension of the work of Cardoso & Zarrebini (Chem. Engng Sci., vol. 56, issue 11, 2001a, pp. 3365–3375), an analytical expression is developed to determine the onset of convection in the environment beyond the edge of the plume, which for a known particle settling velocity, can be used to characterise a plume's expected settling regime. In all plume regimes, the intrusion fluid is observed to rise in the environment following the sedimentation of particles and a simple model for the change in intrusion fluid height has been developed using the steady-state particle concentration at the spreading level.

SO₂ and BrO emissions of Masaya volcano from 2014 to 2020

Masaya (Nicaragua, 12.0∘ N, 86.2∘ W; 635 m a.s.l.) is one of the few volcanoes hosting a lava lake, today. This study has two foci: (1) discussing the state of the art of long-term SO2 emission flux monitoring with the example of Masaya and (2) the provision and discussion of a continuous data set on volcanic gas data with a large temporal coverage, which is a major extension of the empirical database for studies in volcanology as well as atmospheric bromine chemistry. We present time series of SO2 emission fluxes and BrO/SO2 molar ratios in the gas plume of Masaya from March 2014 to March 2020 – covering the three time periods (1) before the lava lake appearance, (2) a period of high lava lake activity (November 2015 to May 2018), and (3) after the period of high lava lake activity. For these three time periods, we report average SO2 emission fluxes of (1000±200), (1000±300), and (700±200) t d−1 and average BrO/SO2 molar ratios of (2.9±1.5)×10-5, (4.8±1.9)×10-5, and (5.5±2.6)×10-5. Our SO2 emission flux retrieval is based on a comprehensive investigation of various aspects of spectroscopic retrievals, the wind conditions, and the plume height. We observed a correlation between the SO2 emission fluxes and the wind speed in the raw data. We present a partial correction of this artefact by applying dynamic estimates for the plume height as a function of the wind speed. Our retrieved SO2 emission fluxes are on average a factor of 1.4 larger than former estimates based on the same data. Further, we observed different patterns in the BrO/SO2 time series: (1) an annual cyclicity with amplitudes between 1.4 and 2.5×10-5 and a weak semi-annual modulation, (2) a step increase by 0.7×10-5 in late 2015, (3) a linear trend of 1.4×10-5 per year from November 2015 to March 2018, and (4) a linear trend of -0.8×10-5 per year from June 2018 to March 2020. The step increase in 2015 coincided with the lava lake appearance and was thus most likely caused by a change in the magmatic system. We suggest that the cyclicity might be a manifestation of meteorological cycles. We found an anti-correlation between the BrO/SO2 molar ratios and the atmospheric water concentration (correlation coefficient of −0.47) but, in contrast to that, neither a correlation with the ozone mixing ratio (+0.21) nor systematic dependencies between the BrO/SO2 molar ratios and the atmospheric plume age for an age range of 2–20 min after the release from the volcanic edifice. The two latter observations indicate an early stop of the autocatalytic transformation of bromide Br− solved in aerosol particles to atmospheric BrO.

Insights into the 9 December 2019 eruption of Whakaari/White Island from analysis of TROPOMI SO2 imagery

Small, phreatic explosions from volcanic hydrothermal systems pose a substantial proximal hazard on volcanoes, which can be popular tourist sites, creating casualty risks in case of eruption. Volcano monitoring of gas emissions provides insights into when explosions are likely to happen and unravel processes driving eruptions. Here, we report SO2 flux and plume height data retrieved from TROPOMI satellite imagery before, during, and after the 9 December 2019 eruption of Whakaari/White Island volcano, New Zealand, which resulted in 22 fatalities and numerous injuries. We show that SO2 was detected without explosive activity on separate days before and after the explosion, and that fluxes increased from 10 to 45 kg/s ~40 min before the explosion itself. High temporal resolution gas monitoring from space can provide key insights into magmatic degassing processes globally, aiding understanding of eruption precursors and complementing ground-based monitoring.

Development of an Inverse Plume Model for Mass Eruption Rate in Unsteady Conditions

Following volcanic eruptions, forecasters need accurate estimates of mass eruption rate (MER) to appropriately predict the downstream effects. Most analyses use simple correlations or models based on large eruptions at steady conditions, even though many volcanoes feature significant unsteadiness. To address this, a superposition model is developed based on a technique used for spray injection applications, which predicts plume height as a function of the time-varying exit velocity. This model can be inverted, providing estimates of MER using field observations of a plume. The model parameters are optimized using laboratory data for plumes with physically-relevant exit profiles and Reynolds numbers, resulting in predictions that agree to within 10% of measured exit velocities. The model performance is examined using a historic eruption from Stromboli with well-documented unsteadiness, again providing MER estimates of the correct order of magnitude. This method can provide a rapid alternative for real-time forecasting of small, unsteady eruptions.

New insights into the ~74 ka Toba eruption from sulfur isotopes of polar ice cores

The ~74 ka Toba eruption was one of the largest volcanic events of the Quaternary. There is much interest in determining the impact of such a huge event, particularly on the climate and hominid populations at the time. Although the Toba eruption has been identified in both land and marine archives as the Youngest Toba Tuff, its precise place in the ice core record is ambiguous. Multiple volcanic sulfate signals have been identified in both Antarctic and Greenland ice cores within the uncertainty of age estimates as possible events for the Toba eruption. We measure sulfur isotope compositions in Antarctic ice samples at high temporal resolution across 11 of these potential Toba sulfate peaks in two cores to identify candidates with sulfur mass-independent fractionation (S-MIF), indicative of an eruption whose plume reached altitudes at or above the ozone layer in the stratosphere. Using this method, we identify several candidate sulfate peaks that contain stratospheric sulfur. We further narrow down potential candidates based on the isotope signatures by identifying sulfate peaks that are due to a volcanic event at tropical latitudes. In one of these sulfate peaks at 73.67 ka, we find the largest ever reported magnitude of S-MIF in volcanic sulfate in polar ice, with a Δ33S value of −4.75 ‰. As there is a positive correlation between the magnitude of the S-MIF signal recorded in ice cores and eruptive plume height, this could be a likely candidate for the Toba supereruption, with a plume height in excess of 45 km. These results support the 73.7 ± 0.3 ka (1σ) ka Ar/Ar age estimate for the eruption, with ice core ages of our candidates with the largest magnitude S-MIF at 73.67 and 73.74 ka. Finally, since these candidate eruptions occurred on the transition into Greenland Stadial 20, the relative timing suggests that Toba was not the trigger for the large Northern Hemisphere cooling at this time although we cannot rule out an amplifying effect.

New insights into magmatic processes from integrated satellite observation, trajectory analysis and magma ascent modelling

&lt;p&gt;Analysis of TROPOMI data with plume trajectory tools opens the possibility of new insights into volcanic / magmatic processes from two data sources: SO2 flux time series and plume height time series. In this paper we investigate results from explosive eruptions and attempt to explain the results with a magma ascent conduit model. The combination of plume height and gas flux data with a model of the magma ascent process provides a toolkit which allows us to constrain magma reservoir processes from satellite monitoring data. The combination of modelling and observations opens a new volcanological research frontier, because the TROPOMI sensor has daily global coverage, a high spatial resolution and is sensitive enough to detect many small-medium explosions globally, so that a large inventory of explosive activity can be characterised.&amp;#160;&lt;/p&gt;

The radius of the umbrella cloud helps characterize large explosive volcanic eruptions

Eruption source parameters (in particular erupted volume and column height) are used by volcanologists to inform volcanic hazard assessments and to classify explosive volcanic eruptions. Estimations of source parameters are associated with large uncertainties due to various factors, including complex tephra sedimentation patterns from gravitationally spreading umbrella clouds. We modify an advection-diffusion model to investigate this effect. Using this model, source parameters for the climactic phase of the 2450 BP eruption of Pululagua, Ecuador, are different with respect to previous estimates (erupted mass: 1.5–5 × 1011 kg, umbrella cloud radius: 10–14 km, plume height: 20–30 km). We suggest large explosive eruptions are better classified by volume and umbrella cloud radius instead of volume or column height alone. Volume and umbrella cloud radius can be successfully estimated from deposit data using one numerical model when direct observations (e.g., satellite images) are not available.

Reimagining futures

As the climate crisis intensifies amid some persistent public denial of the science, there exists a necessary opportunity for scientists to engage in transdisciplinary collaborations, such as those with artists and designers, in an effort to both improve the communication of climate science, but also to bolster the production of scientific knowledge. We demonstrate how art and design can activate the human imagination and promote collaboration across disciplines in a way that the post-Enlightenment scientific endeavor has historically been unable to do and can provide a framework for developing sustainable solutions to the climate crisis. Here, we describe 2 studies that involved collaboration between artists and designers and climate scientists. The first study paired a team of designers and computer scientists with climate and atmospheric scientists from the Jet Propulsion Laboratory in an effort to (re)build an exploratory research interface for the Multi-Angle Spectroradiometer Plume Height Project dataset. This project not only produced an aesthetic visualization interface with highly improved functionality, but it also demonstrated how an improved interface can enable scientists to pursue more and “better” research hypotheses. For the second study, we worked with artists at the School of the Art Institute of Chicago to create three sonic-based art pieces that effectively communicated the science of climate change, appealed to human aesthetic judgment, and expanded the scope of our “ecological awareness.” We show that, while collaborations between artists and scientists are not necessarily novel, the integration of art, design, and science from a project’s inception can improve both the production of knowledge and constitute an entry point for regular people to understand and engage with their rapidly changing planet.