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1
Linan, L., É. Pariat, G. Aulanier, K. Moraitis und G. Valori. „Energy and helicity fluxes in line-tied eruptive simulations“. Astronomy & Astrophysics 636 (April 2020): A41. http://dx.doi.org/10.1051/0004-6361/202037548.
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Context. Conservation properties of magnetic helicity and energy in the quasi-ideal and low-β solar corona make these two quantities relevant for the study of solar active regions and eruptions. Aims. Based on a decomposition of the magnetic field into potential and nonpotential components, magnetic energy and relative helicity can both also be decomposed into two quantities: potential and free energies, and volume-threading and current-carrying helicities. In this study, we perform a coupled analysis of their behaviors in a set of parametric 3D magnetohydrodynamic (MHD) simulations of solar-like eruptions. Methods. We present the general formulations for the time-varying components of energy and helicity in resistive MHD. We calculated them numerically with a specific gauge, and compared their behaviors in the numerical simulations, which differ from one another by their imposed boundary-driving motions. Thus, we investigated the impact of different active regions surface flows on the development of the energy and helicity-related quantities. Results. Despite general similarities in their overall behaviors, helicities and energies display different evolutions that cannot be explained in a unique framework. While the energy fluxes are similar in all simulations, the physical mechanisms that govern the evolution of the helicities are markedly distinct from one simulation to another: the evolution of volume-threading helicity can be governed by boundary fluxes or helicity transfer, depending on the simulation. Conclusions. The eruption takes place for the same value of the ratio of the current-carrying helicity to the total helicity in all simulations. However, our study highlights that this threshold can be reached in different ways, with different helicity-related processes dominating for different photospheric flows. This means that the details of the pre-eruptive dynamics do not influence the eruption-onset helicity-related threshold. Nevertheless, the helicity-flux dynamics may be more or less efficient in changing the time required to reach the onset of the eruption.
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Segonne, Charlotte, Nathalie Huret, Sébastien Payan, Mathieu Gouhier und Valéry Catoire. „A Spectra Classification Methodology of Hyperspectral Infrared Images for Near Real-Time Estimation of the SO2 Emission Flux from Mount Etna with LARA Radiative Transfer Retrieval Model“. Remote Sensing 12, Nr. 24 (16.12.2020): 4107. http://dx.doi.org/10.3390/rs12244107.
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Fast and accurate quantification of gas fluxes emitted by volcanoes is essential for the risk mitigation of explosive eruption, and for the fundamental understanding of shallow eruptive processes. Sulphur dioxide (SO2), in particular, is a reliable indicator to predict upcoming eruptions, and its systemic characterization allows the rapid assessment of sudden changes in eruptive dynamics. In this regard, infrared (IR) hyperspectral imaging is a promising new technology for accurately measure SO2 fluxes day and night at a frame rate down to 1 image per second. The thermal infrared region is not very sensitive to particle scattering, which is an asset for the study of volcanic plume. A ground based infrared hyperspectral imager was deployed during the IMAGETNA campaign in 2015 and provided high spectral resolution images of the Mount Etna (Sicily, Italy) plume from the North East Crater (NEC), mainly. The LongWave InfraRed (LWIR) hyperspectral imager, hereafter name Hyper-Cam, ranges between 850–1300 cm−1 (7.7–11.8 µm). The LATMOS (Laboratoire Atmosphères Milieux Observations Spatiales) Atmospheric Retrieval Algorithm (LARA), which is used to retrieve the slant column densities (SCD) of SO2, is a robust and a complete radiative transfer model, well adapted to the inversion of ground-based remote measurements. However, the calculation time to process the raw data and retrieve the infrared spectra, which is about seven days for the retrieval of one image of SO2 SCD, remains too high to infer near real-time (NRT) SO2 emission fluxes. A spectral image classification methodology based on two parameters extracting spectral features in the O3 and SO2 emission bands was developed to create a library. The relevance is evaluated in detail through tests. From data acquisition to the generation of SO2 SCD images, this method requires only ~40 s per image, which opens the possibility to infer NRT estimation of SO2 emission fluxes from IR hyperspectral imager measurements.
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Calvari, Sonia, Gaetana Ganci, Sónia Victória, Pedro Hernandez, Nemesio Perez, José Barrancos, Vera Alfama et al. „Satellite and Ground Remote Sensing Techniques to Trace the Hidden Growth of a Lava Flow Field: The 2014–2015 Effusive Eruption at Fogo Volcano (Cape Verde)“. Remote Sensing 10, Nr. 7 (12.07.2018): 1115. http://dx.doi.org/10.3390/rs10071115.
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Fogo volcano erupted in 2014–2015 producing an extensive lava flow field in the summit caldera that destroyed two villages, Portela and Bangaeira. The eruption started with powerful explosive activity, lava fountains, and a substantial ash column accompanying the opening of an eruptive fissure. Lava flows spreading from the base of the eruptive fissure produced three arterial lava flows. By a week after the start of the eruption, a master lava tube had already developed within the eruptive fissure and along the arterial flow. In this paper, we analyze the emplacement processes based on observations carried out directly on the lava flow field, remote sensing measurements carried out with a thermal camera, SO2 fluxes, and satellite images, to unravel the key factors leading to the development of lava tubes. These were responsible for the rapid expansion of lava for the ~7.9 km length of the flow field, as well as the destruction of the Portela and Bangaeira villages. The key factors leading to the development of tubes were the low topography and the steady magma supply rate along the arterial lava flow. Comparing time-averaged discharge rates (TADR) obtained from satellite and Supply Rate (SR) derived from SO2 flux data, we estimate the amount and timing of the lava flow field endogenous growth, with the aim of developing a tool that could be used for hazard assessment and risk mitigation at this and other volcanoes.
4
Cox, Daniel, Sebastian F. L. Watt, Frances E. Jenner, Alan R. Hastie, Samantha J. Hammond und Barbara E. Kunz. „Elevated magma fluxes deliver high-Cu magmas to the upper crust“. Geology 48, Nr. 10 (10.06.2020): 957–60. http://dx.doi.org/10.1130/g47562.1.
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Abstract Porphyry Cu-Au ore deposits are globally associated with convergent margins. However, controls on the processing and distribution of the chalcophile elements (e.g., Cu) during convergent margin magmatism remain disputed. Here, we show that magmas feeding many Chilean stratovolcanoes fractionate sulfides with a high-Cu/Ag ratio early in their crustal evolution. These magmas show evidence of lower-crustal garnet and amphibole crystallization, and their degree of sulfide fractionation and Cu depletion increase with both crustal thickness and the extent of garnet fractionation. However, samples from a small proportion of volcanoes with elevated eruptive fluxes depart from this Cu-depleting trend, instead erupting Cu-rich magmas. This implies that at these atypical sites, elevated magma productivity and crustal throughput, potentially facilitated by “pathways” exploiting major crustal fault systems, enable rapid magma transit, avoiding lower-crustal Cu-depleting sulfide fractionation and potentially playing an important role in porphyry ore genesis.
5
Parkhomov, Vladimir, Victor Eselevich und Maksim Eselevich. „Geoeffectiveness of an Eruptive Prominence“. System Analysis & Mathematical Modeling 4, Nr. 2 (26.10.2022): 123–51. http://dx.doi.org/10.17150/2713-1734.2022.4(2).123-151.
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The study examined a chain of phenomena from the Sun to the Earth, which allows to study the mechanism of geoeffectiveness of eruptive prominences propagating from the Sun inside the CME (coronal mass ejections). An eruptive prominence ejected into the solar wind moves with its speed towards the Earth in the form of a DSEP (diamagnetic structure of an eruptive prominence). The contact of the DSEP with the magnetosphere leads to its compression and the passage of the DSEP substance into the magnetosphere. The duration of a magnetospheric disturbance in the form of polar auroras on the dayside, a global amplification of current systems, an increase in charged particle fluxes in the radiation belts, and the generation of irregular pulsations of the Pi2-3 type is determined by the duration of the DSEP. A diagram of the geoeffectiveness of the DSEP has been constructed. The resulting scheme is confirmed by statistical studies of the DSEP in different years of solar activity.
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Liu, Yang, Brian T. Welsch, Gherardo Valori, Manolis K. Georgoulis, Yang Guo, Etienne Pariat, Sung-Hong Park und Julia K. Thalmann. „Changes of Magnetic Energy and Helicity in Solar Active Regions from Major Flares“. Astrophysical Journal 942, Nr. 1 (01.01.2023): 27. http://dx.doi.org/10.3847/1538-4357/aca3a6.
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Abstract Magnetic free energy powers solar flares and coronal mass ejections, and the buildup of magnetic helicity might play a role in the development of unstable structures that subsequently erupt. To better understand the roles of energy and helicity in large flares and eruptions, we have characterized the evolution of magnetic energy and helicity associated with 21 X-class flares from 2010 to 2017. Our sample includes both confined and eruptive events, with 6 and 15 in each category, respectively. Using the Helioseismic and Magnetic Imager vector magnetic field observations from several hours before to several hours after each event, we employ (a) the Differential Affine Velocity Estimator for Vector Magnetograms to determine the photospheric fluxes of energy and helicity, and (b) nonlinear force-free field extrapolations to estimate the coronal content of energy and helicity in source-region fields. Using superposed epoch analysis, we find, on average, the following: (1) decreases in both magnetic energy and helicity, in both photospheric fluxes and coronal content, that persist for a few hours after eruptions, but no clear changes, notably in relative helicity, for confined events; (2) significant increases in the twist of photospheric fields in eruptive events, with twist uncertainties too large in confined events to constrain twist changes (and lower overall twist in confined events); and (3) on longer timescales (event time +12 hr), replenishment of free magnetic energy and helicity content to near preevent levels for eruptive events. For eruptive events, magnetic helicity and free energy in coronal models clearly decrease after flares, with the amounts of decrease proportional to each region’s pre-flare content.
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Layana, Susana, Felipe Aguilera, Germán Rojo, Álvaro Vergara, Pablo Salazar, Juan Quispe, Pablo Urra und Diego Urrutia. „Volcanic Anomalies Monitoring System (VOLCANOMS), a Low-Cost Volcanic Monitoring System Based on Landsat Images“. Remote Sensing 12, Nr. 10 (16.05.2020): 1589. http://dx.doi.org/10.3390/rs12101589.
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The practice of monitoring active volcanoes, includes several techniques using either direct or remote measurements, the latter being more important for volcanoes with limited accessibility. We present the Volcanic Anomalies Monitoring System (VOLCANOMS), a new, online, low-cost and semiautomatic system based on Landsat imagery. This system can detect permanent and/or temporal thermal anomalies in near-infrared (NIR), short-wave infrared (SWIR), and thermal infrared (TIR) bands. VOLCANOMS allows researchers to calculate several thermal parameters, such as thermal radiance, effective temperature, anomaly area, radiative, gas, convective, and total heat, and mass fluxes. We study the eruptive activity of five volcanoes including Krakatau, Stromboli, Fuego, Villarrica and Lascar volcanoes, comparing field and eruptive data with thermal radiance. In the case of Villarrica and Lascar volcanoes, we also compare the thermal radiance and eruptive activity with seismic data. The thermal radiance shows a concordance with the eruptive activity in all cases, whereas a correlation is observed between thermal and seismic data both, in Villarrica and Lascar volcanoes, especially in the case of long-period seismicity. VOLCANOMS is a new and powerful tool that, combined with other techniques, generates robust information for volcanic monitoring.
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Delle Donne, Dario, Alessandro Aiuppa, Marcello Bitetto, Roberto D’Aleo, Mauro Coltelli, Diego Coppola, Emilio Pecora, Maurizio Ripepe und Giancarlo Tamburello. „Changes in SO2 Flux Regime at Mt. Etna Captured by Automatically Processed Ultraviolet Camera Data“. Remote Sensing 11, Nr. 10 (20.05.2019): 1201. http://dx.doi.org/10.3390/rs11101201.
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We used a one-year long SO2 flux record, which was obtained using a novel algorithm for real-time automatic processing of ultraviolet (UV) camera data, to characterize changes in degassing dynamics at the Mt. Etna volcano in 2016. These SO2 flux records, when combined with independent thermal and seismic evidence, allowed for capturing switches in activity from paroxysmal explosive eruptions to quiescent degassing. We found SO2 fluxes 1.5–2 times higher than the 2016 average (1588 tons/day) during the Etna’s May 16–25 eruptive paroxysmal activity, and mild but detectable SO2 flux increases more than one month before its onset. The SO2 flux typically peaked during a lava fountain. Here, the average SO2 degassing rate was ~158 kg/s, the peak emission was ~260 kg/s, and the total released SO2 mass was ~1700 tons (in 3 h on 18 May, 2016). Comparison between our data and prior (2014–2015) results revealed systematic SO2 emission patterns prior to, during, and after an Etna’s paroxysmal phases, which allows us to tentatively identify thresholds between pre-eruptive, syn-eruptive, and post-eruptive degassing regimes.
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Kazachenko, Maria D. „A Database of Magnetic and Thermodynamic Properties of Confined and Eruptive Solar Flares“. Astrophysical Journal 958, Nr. 2 (16.11.2023): 104. http://dx.doi.org/10.3847/1538-4357/ad004e.
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Abstract Solar flares sometimes lead to coronal mass ejections that directly affect Earth's environment. However, a large fraction of flares, including on solar-type stars, are confined flares. What are the differences in physical properties between confined and eruptive flares? For the first time, we quantify the thermodynamic and magnetic properties of hundreds of confined and eruptive flares of GOES class C5.0 and above, 480 flares in total. We first analyze large flares of GOES class M1.0 and above observed by the Solar Dynamics Observatory, 216 flares in total, including 103 eruptive and 113 confined flares, from 2010 until 2016 April; we then look at the entire data set of 480 flares above class C5.0. We compare GOES X-ray thermodynamic flare properties, including peak temperature and emission measure, and active-region (AR) and flare-ribbon magnetic field properties, including reconnected magnetic flux and peak reconnection rate. We find that for fixed peak X-ray flux, confined and eruptive flares have similar reconnection fluxes; however, for fixed peak X-ray flux confined flares have on average larger peak magnetic reconnection rates, are more compact, and occur in larger ARs than eruptive flares. These findings suggest that confined flares are caused by reconnection between more compact, stronger, lower-lying magnetic fields in larger ARs that reorganizes a smaller fraction of these regions’ fields. This reconnection proceeds at faster rates and ends earlier, potentially leading to more efficient flare particle acceleration in confined flares.
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Corradini, Stefano, Lorenzo Guerrieri, Dario Stelitano, Giuseppe Salerno, Simona Scollo, Luca Merucci, Michele Prestifilippo et al. „Near Real-Time Monitoring of the Christmas 2018 Etna Eruption Using SEVIRI and Products Validation“. Remote Sensing 12, Nr. 8 (23.04.2020): 1336. http://dx.doi.org/10.3390/rs12081336.
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On the morning of 24 December 2018, an eruptive event occurred at Etna, which was followed the next day by a strong sequence of shallow earthquakes. The eruptive episode lasted until 30 December, ranging from moderate strombolian to lava fountain activity coupled with vigorous ash/gas emissions and a lava flow effusion toward the eastern volcano flank of Valle del Bove. In this work, the data collected from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instruments on board the Meteosat Second Generation (MSG) geostationary satellite are used to characterize the Etna activity by estimating the proximal and distal eruption parameters in near real time. The inversion of data indicates the onset of eruption on 24 December at 11:15 UTC, a maximum Time Average Discharge Rate (TADR) of 8.3 m3/s, a cumulative lava volume emitted of 0.5 Mm3, and a Volcanic Plume Top Height (VPTH) that reached a maximum altitude of 8 km above sea level (asl). The volcanic cloud ash and SO2 result totally collocated, with an ash amount generally lower than SO2 except on 24 December during the climax phase. A total amount of about 100 and 35 kt of SO2 and ash respectively was emitted during the entire eruptive period, while the SO2 fluxes reached peaks of more than 600 kg/s, with a mean value of about 185 kg/s. The SEVIRI VPTH, ash/SO2 masses, and flux time series have been compared with the results obtained from the ground-based visible (VIS) cameras and FLux Automatic MEasurements (FLAME) networks, and the satellite images collected by the MODerate resolution Imaging Spectroradiometer (MODIS) instruments on board the Terra and Aqua- polar satellites. The analysis indicates good agreement between SEVIRI, VIS camera, and MODIS retrievals with VPTH, ash, and SO2 estimations all within measurement errors. The SEVIRI and FLAME SO2 flux retrievals show significant discrepancies due to the presence of volcanic ash and a gap of data on the FLAME network. The results obtained in this study show the ability of geostationary satellite systems to characterize eruptive events from the source to the atmosphere in near real time during the day and night, thus offering a powerful tool to mitigate volcanic risk on both local population and airspace and to give insight on volcanic processes.
11
Kazachenko, Maria D., George H. Fisher, Brian T. Welsch, Yang Liu und Xudong Sun. „PHOTOSPHERIC ELECTRIC FIELDS AND ENERGY FLUXES IN THE ERUPTIVE ACTIVE REGION NOAA 11158“. Astrophysical Journal 811, Nr. 1 (11.09.2015): 16. http://dx.doi.org/10.1088/0004-637x/811/1/16.
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12
Perri, Silvia, Giuseppe Prete, Gaetano Zimbardo, Domenico Trotta, Lynn B. Wilson III, David Lario, Sergio Servidio, Francesco Valentini und Joe Giacalone. „Interpretation of Flat Energy Spectra Upstream of Fast Interplanetary Shocks“. Astrophysical Journal 950, Nr. 1 (01.06.2023): 62. http://dx.doi.org/10.3847/1538-4357/acc942.
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Abstract Interplanetary shocks are large-scale heliospheric structures often caused by eruptive phenomena at the Sun, and represent one of the main sources of energetic particles. Several interplanetary (IP) shock crossings by spacecraft at 1 au have revealed enhanced energetic-ion fluxes that extend far upstream of the shock. Surprisingly, in some shock events ion fluxes with energies between 100 keV and about 2 MeV acquire similar values (which we refer to as “overlapped” fluxes), corresponding to flat energy spectra in that range. In contrast, closer to the shock the fluxes are observed to depend on energy. In this work, we analyze three IP-shock-related energetic particle events observed by the Advanced Composition Explorer spacecraft where flat ion energy spectra were observed upstream of the shock. We interpret these observations via a velocity-filter mechanism for particles in a given energy range. In particular, ions with velocity parallel to the local magnetic field larger than the speed of the upstream plasma, in the reference frame of the shock, can easily propagate back upstream, while lower-energy ions tend to be confined to the shock front, thus reducing their fluxes far upstream and giving rise to flat energy spectra. The velocity-filter mechanism has been corroborated from observations of particle flux anisotropy by the Solid-State Telescope of Wind/3DP.
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Dorman, L. I., N. G. Ptitsyna, G. Villoresi, V. V. Kasinsky, N. N. Lyakhov und M. I. Tyasto. „Space storms as natural hazards“. Advances in Geosciences 14 (10.04.2008): 271–75. http://dx.doi.org/10.5194/adgeo-14-271-2008.
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Abstract. Eruptive activity of the Sun produces a chain of extreme geophysical events: high-speed solar wind, magnetic field disturbances in the interplanetary space and in the geomagnetic field and also intense fluxes of energetic particles. Space storms can potentially destroy spacecrafts, adversely affect astronauts and airline crew and human health on the Earth, lead to pipeline breaking, melt electricity transformers, and discontinue transmission. In this paper we deal with two consequences of space storms: (i) rise in failures in the operation of railway devices and (ii) rise in myocardial infarction and stroke incidences.
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Tschernitz, Johannes, Astrid M. Veronig, Julia K. Thalmann, Jürgen Hinterreiter und Werner Pötzi. „Reconnection Fluxes in Eruptive and Confined Flares and Implications for Superflares on the Sun“. Astrophysical Journal 853, Nr. 1 (22.01.2018): 41. http://dx.doi.org/10.3847/1538-4357/aaa199.
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Guo, J. H., Y. W. Ni, Y. Guo, C. Xia, B. Schmieder, S. Poedts, Z. Zhong, Y. H. Zhou, F. Yu und P. F. Chen. „Data-driven Modeling of a Coronal Magnetic Flux Rope: From Birth to Death“. Astrophysical Journal 961, Nr. 1 (01.01.2024): 140. http://dx.doi.org/10.3847/1538-4357/ad088d.
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Abstract Magnetic flux ropes are a bundle of twisted magnetic field lines produced by internal electric currents, which are responsible for solar eruptions and are the major drivers of geomagnetic storms. As such, it is crucial to develop a numerical model that can capture the entire evolution of a flux rope, from its birth to death, in order to predict whether adverse space weather events might occur or not. In this paper, we develop a data-driven modeling that combines a time-dependent magnetofrictional approach with a thermodynamic magnetohydrodynamic model. Our numerical modeling successfully reproduces the formation and confined eruption of an observed flux rope, and unveils the physical details behind the observations. Regarding the long-term evolution of the active region, our simulation results indicate that the flux cancellation due to collisional shearing plays a critical role in the formation of the flux rope, corresponding to a substantial increase in magnetic free energy and helicity. Regarding the eruption stage, the deformation of the flux rope during its eruption can cause an increase in the downward tension force, which suppresses it from further rising. This finding may shed light on why some torus-unstable flux ropes lead to failed eruptions after large-angle rotations. Moreover, we find that twisted fluxes can accumulate during confined eruptions, which would breed the subsequent eruptive flares.
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Afanasyev, Andrey N., Yuhong Fan, Maria D. Kazachenko und Mark C. M. Cheung. „Hybrid Data-driven Magnetofrictional and Magnetohydrodynamic Simulations of an Eruptive Solar Active Region“. Astrophysical Journal 952, Nr. 2 (24.07.2023): 136. http://dx.doi.org/10.3847/1538-4357/acd7e9.
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Abstract We present the first results of the hybrid data-driven magnetofrictional (MF) and data-constrained magnetohydrodynamic (MHD) simulations of solar active region NOAA 11158, which produced an X-class flare and coronal mass ejection on 2011 February 15. First, we apply the MF approach to build the coronal magnetic configuration corresponding to the SDO/HMI photospheric magnetograms by using the JSOC PDFI_SS electric field inversions at the bottom boundary of the simulation domain. We then use the preeruptive MF state at about 1.5 hr before the observed X-class flare as the initial state for the MHD simulation, assuming a stratified polytropic solar corona. The MHD run shows that the initial magnetic configuration containing twisted magnetic fluxes and a three-dimensional (3D) magnetic null point is out of equilibrium. We find the eruption of a complex magnetic structure consisting of two magnetic flux ropes, as well as the development of flare ribbons, with their morphology being in good agreement with observations. We conclude that the combination of the data-driven MF and data-constrained MHD simulations is a useful practical tool for understanding the 3D magnetic structures of real solar ARs that are unobservable otherwise.
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Dehghanniri, Vahid, und A. Mark Jellinek. „An experimental study of volcanic tremor driven by magma wagging“. Geophysical Journal International 228, Nr. 3 (10.11.2021): 1577–606. http://dx.doi.org/10.1093/gji/ggab404.
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SUMMARY Protracted episodes of 0.5–7 Hz pre-eruptive volcanic tremor (PVT) are common at active stratovolcanoes. Reliable links to processes related to magma movement consequently enable a potential to use properties of PVT as diagnostic eruptive precursors. A challenging feature of PVT is that generic spectral and amplitude properties of the signal evolve similarly, independent of widely varying volcano structures and conduit geometries on which most physical models rely. The ‘magma wagging’ model introduced in Jellinek & Bercovici (2011) and extended by Bercovici et al. (2013), Liao et al. and Liao & Bercovici (2018) makes progress because it depends on magma dynamics that are only weakly sensitive to volcano architecture: The flow of gas through a permeable foamy annulus of gas bubbles excites, modulates and maintains a wagging oscillation of a central magma column rising in an erupting conduit. ‘Magma wagging’ and resulting PVT are driven through an energy transfer from a ‘Bernoulli mode’ related to azimuthal variations in annular gas flow speeds. Consistent with observations, spectral and amplitude properties of PVT are predicted to evolve before an eruption as the width of the annulus decreases with increased gas fluxes. To confirm this critical Bernoulli-to-wagging energy transfer we use extensive experiments and restricted numerical simulations on wagging oscillations excited on analogue viscoelastic columns by annular air flows. We also explore sensitivities of the spatial and temporal characters of wagging to asymmetric annular air flows that are intractable in the existing magma wagging model and expected to occur in nature with spatial variations in annulus permeability. From high-resolution time-series of linear and orbital displacements of analogue column tops and time-series of axial deflections and accelerations of the column centre line, we characterize the excitation, evolution, and steady-state oscillations in unprecedented detail over a broad range of conditions. We show that the Bernoulli mode corresponds to the timescale for the buildup of axial elastic bending stresses in response to pressure variations related to air flows over the heights of columns. We identify three distinct wagging modes: (i) rotational (cf. Liao et al. 2018); (ii) mixed-mode and (iii) chaotic. Rotational modes are favoured for symmetric, high intensity forcing and a maximal delivery of mechanical energy to the fundamental magma wagging mode. Mixed-mode oscillations regimes are favoured for a symmetric, intermediate intensity forcing. Chaotic modes, involving the least efficient delivery of energy to the fundamental mode, occur for asymmetric forcing and where the intensity of imposed airflow is low. Numerical simulations also show that where forcing frequencies are comparable to a natural mode of free oscillation, power delivered by peripheral air flows is concentrated at the lowest frequency fundamental mode generally and spread among higher frequency natural modes where air pressure and column elastic forces are comparable. Our combined experimental and numerical results make qualitative predictions for the evolution of the character of volcanic tremor and its expression in seismic or infrasound arrays during natural events that is testable in field-based studies of PVT and syn-eruptive volcanic tremor.
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Dehghanniri, Vahid, und A. Mark Jellinek. „An experimental study of volcanic tremor driven by magma wagging“. Geophysical Journal International 228, Nr. 3 (10.11.2021): 1577–606. http://dx.doi.org/10.1093/gji/ggab404.
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SUMMARY Protracted episodes of 0.5–7 Hz pre-eruptive volcanic tremor (PVT) are common at active stratovolcanoes. Reliable links to processes related to magma movement consequently enable a potential to use properties of PVT as diagnostic eruptive precursors. A challenging feature of PVT is that generic spectral and amplitude properties of the signal evolve similarly, independent of widely varying volcano structures and conduit geometries on which most physical models rely. The ‘magma wagging’ model introduced in Jellinek & Bercovici (2011) and extended by Bercovici et al. (2013), Liao et al. and Liao & Bercovici (2018) makes progress because it depends on magma dynamics that are only weakly sensitive to volcano architecture: The flow of gas through a permeable foamy annulus of gas bubbles excites, modulates and maintains a wagging oscillation of a central magma column rising in an erupting conduit. ‘Magma wagging’ and resulting PVT are driven through an energy transfer from a ‘Bernoulli mode’ related to azimuthal variations in annular gas flow speeds. Consistent with observations, spectral and amplitude properties of PVT are predicted to evolve before an eruption as the width of the annulus decreases with increased gas fluxes. To confirm this critical Bernoulli-to-wagging energy transfer we use extensive experiments and restricted numerical simulations on wagging oscillations excited on analogue viscoelastic columns by annular air flows. We also explore sensitivities of the spatial and temporal characters of wagging to asymmetric annular air flows that are intractable in the existing magma wagging model and expected to occur in nature with spatial variations in annulus permeability. From high-resolution time-series of linear and orbital displacements of analogue column tops and time-series of axial deflections and accelerations of the column centre line, we characterize the excitation, evolution, and steady-state oscillations in unprecedented detail over a broad range of conditions. We show that the Bernoulli mode corresponds to the timescale for the buildup of axial elastic bending stresses in response to pressure variations related to air flows over the heights of columns. We identify three distinct wagging modes: (i) rotational (cf. Liao et al. 2018); (ii) mixed-mode and (iii) chaotic. Rotational modes are favoured for symmetric, high intensity forcing and a maximal delivery of mechanical energy to the fundamental magma wagging mode. Mixed-mode oscillations regimes are favoured for a symmetric, intermediate intensity forcing. Chaotic modes, involving the least efficient delivery of energy to the fundamental mode, occur for asymmetric forcing and where the intensity of imposed airflow is low. Numerical simulations also show that where forcing frequencies are comparable to a natural mode of free oscillation, power delivered by peripheral air flows is concentrated at the lowest frequency fundamental mode generally and spread among higher frequency natural modes where air pressure and column elastic forces are comparable. Our combined experimental and numerical results make qualitative predictions for the evolution of the character of volcanic tremor and its expression in seismic or infrasound arrays during natural events that is testable in field-based studies of PVT and syn-eruptive volcanic tremor.
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Katsova, M. M., J. J. Drake und M. A. Livshits. „Post-Eruptive Flare Energy Release as Detected on AU Mic by EUVE“. International Astronomical Union Colloquium 152 (1996): 175–80. http://dx.doi.org/10.1017/s0252921100035934.
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The long-duration emission arising after the impulsive rise and decay in a flaring event observed by the Extreme Ultraviolet Explorer on the red dwarf star AU Mic is discussed. The decay of the intensity in the Deep Survey 65–190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with the typical for the flare plasma density. The temporal behavior of the emission measure is determined for both the 65–190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1–2000 Å region over nearly 12 hrs is 3 · 1035 ergs. We first point out some difficulties with earlier explanations proposed for this event; we then propose the following physical model: the source of the prolonged emission is a system of high coronal loops, the size of which is more than the active region scale, but less than the stellar radius. Such systems are observed in soft X-rays during large solar flares after coronal mass ejections. Some additional post-flare energy input into this high coronal loop system can be caused by reconnection in a vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.Apparently, we are faced here with new kind of the surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events the subgiants components of the RS CVn binaries.
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Park, Sunkyung, Ágnes Kóspál, Fernando Cruz-Sáenz de Miera, Michał Siwak, Marek Dróżdż, Bernadett Ignácz, Daniel T. Jaffe et al. „V899 Mon: A Peculiar Eruptive Young Star Close to the End of Its Outburst“. Astrophysical Journal 923, Nr. 2 (01.12.2021): 171. http://dx.doi.org/10.3847/1538-4357/ac29c4.
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Abstract The eruptive young star V899 Mon shows characteristics of both FUors and EXors. It reached a peak brightness in 2010, then briefly faded in 2011, followed by a second outburst. We conducted multifilter optical photometric monitoring, as well as optical and near-infrared spectroscopic observations, of V899 Mon. The light curves and color–magnitude diagrams show that V899 Mon has been gradually fading after its second outburst peak in 2018, but smaller accretion bursts are still happening. Our spectroscopic observations taken with Gemini/IGRINS and VLT/MUSE show a number of emission lines, unlike during the outbursting stage. We used the emission line fluxes to estimate the accretion rate and found that it has significantly decreased compared to the outbursting stage. The mass-loss rate is also weakening. Our 2D spectroastrometric analysis of emission lines recovered jet and disk emission of V899 Mon. We found that the emission from permitted metallic lines and the CO bandheads can be modeled well with a disk in Keplerian rotation, which also gives a tight constraint for the dynamical stellar mass of 2 M ⊙. After a discussion of the physical changes that led to the changes in the observed properties of V899 Mon, we suggest that this object is finishing its second outburst.
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Mishev, Alexander, und Piers Jiggens. „Preface to measurement, specification and forecasting of the Solar Energetic Particle (SEP) environment and Ground Level Enhancements (GLEs)“. Journal of Space Weather and Space Climate 9 (2019): E1. http://dx.doi.org/10.1051/swsc/2019003.
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The Sun emits energetic particles following eruptive events such as solar flares and Coronal Mass Ejections (CMEs). Solar Energetic Particles (SEPs) arrive in bursts known as Solar Particle Events (SPEs), which penetrate into the Earth’s magnetosphere. SEPs with large enough energy induce a complicated atmospheric cascade, which secondary particles lead to an enhancement of count rate of ground-based detectors e.g. Neutron Monitors (NMs). This class of SEPs is therefore referred as Ground Level Enhancements (GLEs). The characterisation of the high-energy SEPs environment with corresponding space weather effects is important for space flights, aviation, and satellite industry. In this topical issue recent developments, addressing important user needs in the space radiation environment domain are published. Some articles are relevant to the specification of the SEP environment whilst others focus on space weather prediction of SEP fluxes. Catalogues based on measurement and processing of SEPs including ground-based data, and modelling of aircrew radiation exposure during major events are also presented.
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Vidotto, A. A., R. Fares, M. Jardine, C. Moutou und J. F. Donati. „The particle and magnetic environments surrounding close-in exoplanets“. Proceedings of the International Astronomical Union 11, S320 (August 2015): 397–402. http://dx.doi.org/10.1017/s1743921315010698.
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AbstractThe proper characterisation of stellar winds is essential for the study of propagation of eruptive events (flares, coronal mass ejections) and the study of space weather events on exoplanets. Here, we quantitatively investigate the nature of the stellar winds surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the three-dimensional winds of their host stars, in which we directly incorporate their observed surface magnetic fields. With that, we derive the wind properties at the position of the hot-Jupiters’ orbits (temperature, velocity, magnetic field intensity and pressure). We show that the exoplanets studied here are immersed in a local stellar wind that is much denser than the local conditions encountered around the solar system planets (e.g., 5 orders of magnitude denser than the conditions experienced by the Earth). The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (2 to 3 orders of magnitude larger than the interplanetary medium surrounding the Earth). The characterisation of the host star's wind is also crucial for the study of how the wind interacts with exoplanets. For example, we compute the exoplanetary radio emission that is released in the wind-exoplanet interaction. For the hot-Jupiters studied here, we find radio fluxes ranging from 0.02 to 0.13 mJy. These fluxes could become orders of magnitude higher when stellar eruptions impact exoplanets, increasing the potential of detecting exoplanetary radio emission.
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Zhou, Ying, Philip A. E. Pogge von Strandmann, Maoyan Zhu, Hongfei Ling, Christina Manning, Da Li, Tianchen He und Graham A. Shields. „Reconstructing Tonian seawater 87Sr/86Sr using calcite microspar“. Geology 48, Nr. 5 (14.02.2020): 462–67. http://dx.doi.org/10.1130/g46756.1.
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Abstract The Tonian Period followed a long interval of relative stasis and led into the climatic extremes and biological radiations of multicellular life during the Cryogenian and Ediacaran Periods, respectively. However, despite its pivotal situation, it remains relatively understudied, in large part due to the lack of robust age constraints. A combination of fossil evidence, radiometric ages, and isotopic constraints reveal that carbonate strata on the North China craton were deposited between ca. 980 and ca. 920 Ma, thereby filling a gap in marine archives. Here we present 87Sr/86Sr data from selected calcite microspar cements, which filled early diagenetic “molar tooth” cracks, along with data from demonstrably well-preserved bulk carbonate samples. These new data show that seawater 87Sr/87Sr rose in stages from ∼0.7052 at ca. 980 Ma to ∼0.7063 by ca. 920 Ma, after which a return to low values coincided with the eruption of the Dashigou large igneous province across the North China craton. We also present a new Neoproterozoic seawater 87Sr/86Sr curve, which reveals that the general trend toward higher 87Sr/87Sr during the Tonian Period was checked repeatedly by the input of less-radiogenic strontium from a series of eruptive events, both coincident with and prior to the main breakup of Rodinia. The weathering of Tonian volcanic provinces has been linked to higher carbon burial, glaciation, and oxygenation due to the high phosphorus content of flood basalts. Here we show that the weathering of major volcanic provinces affected material fluxes and ocean chemistry much earlier than previously envisaged.
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Struminsky, A. B., I. Yu Grigorieva, Yu I. Logachev und A. M. Sadovskii. „Solar relativistic electrons and protons on October 28, 2021 (GLE73)“. Известия Российской академии наук. Серия физическая 87, Nr. 7 (01.07.2023): 1023–27. http://dx.doi.org/10.31857/s0367676523701818.
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The proton event of October 28, 2021, which was accompanied by the first in the current 25th cycle and the 73rd in the history of observations, a ground-based enhancement in the intensity of cosmic rays (GLE73), is considered. The development of the parent flare lasted more than 10 min against the background of the highest energy release simultaneously creating the conditions both for acceleration of the coronal mass ejection (CME) and acceleration of charged particles to relativistic energies. The similarity of time intensity profiles of relativistic electrons and protons in the Earth’s orbit indicates a stochastic mechanism of their acceleration. The X1.0 eruptive flare on October 28, 2021, is similar in hard X-ray emission to the M5.1 flare on May 17, 2012 (GLE71). The relatively late start of the increase in the fluxes of relativistic electrons and protons in the Earth’s orbit compared to the GLE71 event is explained by the location of the flare on October 28, 2021 (S26W05) and the southward launch of the CME.
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Pritchard, M. E., T. A. Mather, S. R. McNutt, F. J. Delgado und K. Reath. „Thoughts on the criteria to determine the origin of volcanic unrest as magmatic or non-magmatic“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, Nr. 2139 (07.01.2019): 20180008. http://dx.doi.org/10.1098/rsta.2018.0008.
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As our ability to detect volcanic unrest improves, we are increasingly confronted with the question of whether the unrest has a magmatic origin (magma on the move) or a non-magmatic origin from a change in the hydrothermal system (fluids that are not magma on the move) or tectonic processes. The cause of unrest has critical implications for the potential eruptive hazard (e.g. used in constructing Bayesian Event Trees), but is frequently the subject of debate, even at well-studied systems. Here, we propose a set of multi-disciplinary observations and numerical models that could be used to evaluate conceptual models about the cause of unrest. These include measurements of gas fluxes and compositions and the isotopic signature of some components (e.g. H 2 , He, C, SO 2 , H 2 O , CH 4 and CO 2 ), the spatial and temporal characteristics of ground deformation, thermal output, seismicity, changes in gravity, and whether there is topographic uplift or subsidence spanning hundreds to thousands of years. In several volcanic systems, both magmatic and non-magmatic unrest is occurring at the same time. While none of these observations or models is diagnostic on its own, we illustrate several examples where they have been used together to make a plausible conceptual model of one or more episodes of unrest and whether eruptions did or did not follow the unrest. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.
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Masson, Sophie, Étienne Pariat, Gherardo Valori, Na Deng, Chang Liu, Haimin Wang und Hamish Reid. „Flux rope, hyperbolic flux tube, and late extreme ultraviolet phases in a non-eruptive circular-ribbon flare“. Astronomy & Astrophysics 604 (August 2017): A76. http://dx.doi.org/10.1051/0004-6361/201629654.
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Context. The dynamics of ultraviolet (UV) emissions during solar flares provides constraints on the physical mechanisms involved in the trigger and the evolution of flares. In particular it provides some information on the location of the reconnection sites and the associated magnetic fluxes. In this respect, confined flares are far less understood than eruptive flares generating coronal mass ejections. Aims. We present a detailed study of a confined circular flare dynamics associated with three UV late phases in order to understand more precisely which topological elements are present and how they constrain the dynamics of the flare. Methods. We perform a non-linear force-free field extrapolation of the confined flare observed with the Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) instruments on board Solar Dynamics Observatory (SDO). From the 3D magnetic field we compute the squashing factor and we analyse its distribution. Conjointly, we analyse the AIA extreme ultraviolet (EUV) light curves and images in order to identify the post-flare loops, and their temporal and thermal evolution. By combining the two analyses we are able to propose a detailed scenario that explains the dynamics of the flare. Results. Our topological analysis shows that in addition to a null-point topology with the fan separatrix, the spine lines and its surrounding quasi-separatix layer (QSL) halo (typical for a circular flare), a flux rope and its hyperbolic flux tube (HFT) are enclosed below the null. By comparing the magnetic field topology and the EUV post-flare loops we obtain an almost perfect match between the footpoints of the separatrices and the EUV 1600 Å ribbons and between the HFT field line footpoints and bright spots observed inside the circular ribbons. We show, for the first time in a confined flare, that magnetic reconnection occurred initially at the HFT below the flux rope. Reconnection at the null point between the flux rope and the overlying field is only initiated in a second phase. In addition, we showed that the EUV late phase observed after the main flare episode is caused by the cooling loops of different length which have all reconnected at the null point during the impulsive phase. Conclusions. Our analysis shows in one example that flux ropes are present in null-point topology not only for eruptive and jet events, but also for confined flares. This allows us to conjecture on the analogies between conditions that govern the generation of jets, confined flares or eruptive flares.
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Rogic, Nikola, Annalisa Cappello, Gaetana Ganci, Alessandro Maturilli, Hazel Rymer, Stephen Blake und Fabrizio Ferrucci. „Spaceborne EO and a Combination of Inverse and Forward Modelling for Monitoring Lava Flow Advance“. Remote Sensing 11, Nr. 24 (16.12.2019): 3032. http://dx.doi.org/10.3390/rs11243032.
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We aim here to improve the understanding of the relationship between emissivity of the lava and temperature by carrying out a multi-stage experiment for the 2017 Mt Etna (Italy) eruption. We combine laboratory, spaceborne, and numerical modelling data, to quantify the emissivity–temperature relationship. Our laboratory-based Fourier-transform infrared (FTIR) results indicate that emissivity and temperature are inversely correlated, which supports the argument that emissivity of molten material is significantly lower than that of the same material in its solid state. Our forward-modelling tests using MAGFLOW Cellular Automata suggest that a 35% emissivity variation (0.95 to 0.60) can produce up to 46% overestimation (for constant emissivity 0.60) in simulated/forecasted lava flow lengths (compared to actual observed). In comparison, our simulation using a ‘two-component’ emissivity approach (i.e., different emissivity values for melt and cooled lava) and constant emissivity 0.95 compares well (≤10% overestimation) with the actual 2017 lava flow lengths. We evaluated the influence of variable emissivity on lava surface temperatures using spaceborne data by performing several parametrically controlled assessments, using both constant (‘uniform’) and a ‘two-component’ emissivity approach. Computed total radiant fluxes, using the same spaceborne scene (Landsat 8 Operational Land Imager (OLI)), differ ≤15% depending on emissivity endmembers (i.e., 0.95 and 0.60). These results further suggest that computed radiant flux using high-spatial resolution data is bordering at lower boundary (range) values of the moderate-to-high temporal resolution spaceborne data (i.e., Moderate Resolution Imaging Spectroradiometer (MODIS) and Spinning Enhanced Visible and Infrared Imager (SEVIRI)), acquired for the same target area (and the same time interval). These findings may have considerable impact on civil protection decisions made during volcanic crisis involving lava flows as they approach protected or populated areas. Nonetheless, the laboratory work, reported here, should be extended to include higher volcanic eruptive temperatures (up to 1350 K).
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Kazachenko, Maria D., Benjamin J. Lynch, Antonia Savcheva, Xudong Sun und Brian T. Welsch. „Toward Improved Understanding of Magnetic Fields Participating in Solar Flares: Statistical Analysis of Magnetic Fields within Flare Ribbons“. Astrophysical Journal 926, Nr. 1 (01.02.2022): 56. http://dx.doi.org/10.3847/1538-4357/ac3af3.
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Abstract Violent solar flares and coronal mass ejections (CMEs) are magnetic phenomena. However, how magnetic fields reconnecting in the flare differ from nonflaring magnetic fields remains unclear owing to the lack of studies of the flare magnetic properties. Here we present a first statistical study of flaring (highlighted by flare ribbons) vector magnetic fields in the photosphere. Our systematic approach allows us to describe the key physical properties of solar flare magnetism, including distributions of magnetic flux, magnetic shear, vertical current, and net current over flaring versus nonflaring parts of the active region (AR), and compare these with flare/CME properties. Our analysis suggests that while flares are guided by the physical properties that scale with AR size, like the total amount of magnetic flux that participates in the reconnection process and the total current (extensive properties), CMEs are guided by mean properties, like the fraction of the AR magnetic flux that participates (intensive property), with little dependence on the amount of shear at the polarity inversion line (PIL) or the net current. We find that the nonneutralized current is proportional to the amount of shear at the PIL, providing direct evidence that net vertical currents are formed as a result of any mechanism that could generate magnetic shear along the PIL. We also find that eruptive events tend to have smaller PIL fluxes and larger magnetic shears than confined events. Our analysis provides a reference for more realistic solar and stellar flare models. The database is available online and can be used for future quantitative studies of flare magnetism.
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Torres, Roberto, Hiroyuki Kumagai und Kimiko Taguchi. „Source models of long-period seismic events at Galeras volcano, Colombia“. Geophysical Journal International 227, Nr. 3 (14.08.2021): 2137–55. http://dx.doi.org/10.1093/gji/ggab325.
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SUMMARY Long-period (LP) seismic events have occurred repeatedly at Galeras volcano, Colombia, during the transition from effusive dome formation to explosive Vulcanian eruptions. Since 1989, two types of LP events have been observed there: one characterized by long-lasting, decaying harmonic oscillations (NLP events) and the other by non-harmonic oscillatory features (BLP events). NLP events are attributed to resonances of a dusty gas-filled crack in the magma plugging the eruptive conduit. Sixteen episodes of NLP events occurred at Galeras during 1992–2010, each characterized by systematic temporal variations in the frequencies and quality factors of NLP events. Our and previous estimates of crack model parameters during three of those NLP episodes indicate that the similar temporal variations in crack geometry and fluid properties can be explained by an increase in the ash content within the crack and a decrease in crack volume. We found that NLP events, associated with low SO2 fluxes, are anticorrelated with BLP events, which are accompanied by high SO2 emissions. From our observations and analytical results, we inferred that BLP events are generated by resonances of open cracks in the uppermost magma plug, corresponding to tuffisite veins, that efficiently transfer volcanic gases. After sufficient degassing and densification, the magma plug effectively seals the conduit. The growing overpressure in the deeper magma is then released through a shear fracture along the conduit margin. The intrusion of deeper, vesiculated magma into the shear fracture depressurizes and fragments the magma, producing a dusty gas and triggering the crack resonances that generate NLP events. Our results thus indicate that the evolution of the properties of the magma plug controls the occurrences of BLP and NLP events at Galeras. Although NLP events do not always precede explosive eruptions, they indicate that an important overpressure is building in the shallow conduit.
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Eselevich, Viktor, und Vladimir Parhomov. „Role of alpha particles in penetration of solar wind diamagnetic structures into the magnetosphere“. Solar-Terrestrial Physics 9, Nr. 3 (30.09.2023): 10–20. http://dx.doi.org/10.12737/stp-93202302.
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We present the results of studies showing the presence of simultaneous jumps in the density of protons (N2/N1)p and alpha particles (N2/N1)α at the boundaries of diamagnetic structures (DS) of various types both in the quasi-stationary slow solar wind (SW) and in sporadic SW. For DS of quasi-stationary slow SW, associated with streamer belt or chains, in the statistics considered in the paper there is a single linear dependence of (N2/N1)α on (N2/N1)p. This means that these jumps have the same physical nature and are related to diamagnetism at the boundaries of DS of quasi-stationary SW streams of various types.
At the front of interplanetary shock waves (ISW), the (N2/N1)α jump is approximately twice as large as the (N2/N1)p jump. This reflects the features of the collective collisionless plasma heating at ISW fronts and requires further studies. A maximum excess (almost 3 times) of the increase in the alpha-particle density (N2/N1)α over the increase in the proton density (N2/N1)p is observed in eruptive prominences.
The magnetospheric response in such phenomena as auroras, proton and alpha particle fluxes, geomagnetic field, and geomagnetic pulsations is similar under the influence of DS of various types and ISW. The detected features of the magnetospheric response to the contact with DS of different types and ISW can be interpreted as impulsive passage of the DS matter (plasmoid) into the magnetosphere.
The results of studies of the (N2/N1)α jumps can be used as an additional important argument in identifying cases of impulsive penetration of DS into the magnetosphere and in examining the physical nature of these penetrations.
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Eselevich, Viktor, und Vladimir Parhomov. „Role of alpha particles in penetration of solar wind diamagnetic structures into the magnetosphere“. Solnechno-Zemnaya Fizika 9, Nr. 3 (29.09.2023): 12–22. http://dx.doi.org/10.12737/szf-93202302.
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We present the results of studies showing the presence of simultaneous jumps in the density of protons (N2/N1)p and alpha particles (N2/N1)α at the boundaries of diamagnetic structures (DS) of various types both in the quasi-stationary slow solar wind (SW) and in sporadic SW. For DS of quasi-stationary slow SW, associated with streamer belt or chains, in the statistics considered in the paper there is a single linear dependence of (N2/N1)α on (N2/N1)p. This means that these jumps have the same physical nature and are related to diamagnetism at the boundaries of DS of quasi-stationary SW streams of various types.
At the front of interplanetary shock waves (ISW), the (N2/N1)α jump is approximately twice as large as the (N2/N1)p jump. This reflects the features of the collective collisionless plasma heating at ISW fronts and requires further studies. A maximum excess (almost 3 times) of the increase in the alpha-particle density (N2/N1)α over the increase in the proton density (N2/N1)p is observed in eruptive prominences.
The magnetospheric response in such phenomena as auroras, proton and alpha particle fluxes, geomagnetic field, and geomagnetic pulsations is similar under the influence of DS of various types and ISW. The detected features of the magnetospheric response to the contact with DS of different types and ISW can be interpreted as impulsive passage of the DS matter (plasmoid) into the magnetosphere.
The results of studies of the (N2/N1)α jumps can be used as an additional important argument in identifying cases of impulsive penetration of DS into the magnetosphere and in examining the physical nature of these penetrations.
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Gavrilenko, Maxim, Michael Krawczynski, Philipp Ruprecht, Wenlu Li und Jeffrey G. Catalano. „The quench control of water estimates in convergent margin magmas“. American Mineralogist 104, Nr. 7 (01.07.2019): 936–48. http://dx.doi.org/10.2138/am-2019-6735.
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AbstractHere we present a study on the quenchability of hydrous mafic melts. We show via hydrothermal experiments that the ability to quench a mafic hydrous melt to a homogeneous glass at cooling rates relevant to natural samples has a limit of no more than 9 ± 1 wt% of dissolved H2O in the melt. We performed supra-liquidus experiments on a mafic starting composition at 1–1.5 GPa spanning H2O-undersaturated to H2O-saturated conditions (from ~1 to ~21 wt%). After dissolving H2O and equilibrating, the hydrous mafic melt experiments were quenched. Quenching rates of 20 to 90 K/s at the glass transition temperature were achieved, and some experiments were allowed to decompress from thermal contraction while others were held at an isobaric condition during quench. We found that quenching of a hydrous melt to a homogeneous glass at quench rates comparable to natural conditions is possible at water contents up to 6 wt%. Melts containing 6–9 wt% of H2O are partially quenched to a glass, and always contain significant fractions of quench crystals and glass alteration/devitrification products. Experiments with water contents greater than 9 wt% have no optically clear glass after quench and result in fine-grained mixtures of alteration/devitrification products (minerals and amorphous materials). Our limit of 9 ± 1 wt% agrees well with the maximum of dissolved H2O contents found in natural glassy melt inclusions (8.5 wt% H2O). Other techniques for estimating pre-eruptive dissolved H2O content using petrologic and geochemical modeling have been used to argue that some arc magmas are as hydrous as 16 wt% H2O. Thus, our results raise the question of whether the observed record of glassy melt inclusions has an upper limit that is partially controlled by the quenching process. This potentially leads to underestimating the maximum amount of H2O recycled at arcs when results from glassy melt inclusions are predominantly used to estimate water fluxes from the mantle.
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Lavigne, Frank, und Jean-Claude Thouret. „Les lahars; depots, origines et dynamique“. Bulletin de la Société Géologique de France 171, Nr. 5 (01.09.2000): 545–57. http://dx.doi.org/10.2113/171.5.545.
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Abstract A lahar is a flowing mixture of rock debris and water (other than normal streamflow) from a volcano, which encompasses a continuum from debris flows (sediment concentration > or =60% per volume) to hyperconcentrated streamflows (sediment concentration from 20 to 60% per volume). Debris flow deposits are poorly sorted and massive with abundant clasts. Lahars can be either syn-eruptive, post-eruptive or have a non-eruptive origin. Four types of lahars can be generated during an eruption, based on distinct sources of water (i.e. ice, snow, crater lake, river, and rain) that allow the sediments to be removed and incorporated in the lahar (e.g., Mount St.-Helens in 1980, Nevado del Ruiz in 1985). Post-eruptive lahars, which are rain-triggered, occur during several years after an eruption (e.g., still occurring at Pinatubo). Non-eruptive lahars are flows generated on volcanoes without eruptive activity, particularly in the case of a debris avalanche or a lake outburst (e.g., Kelud or Ruapehu). Lahars flow as pulses, whose velocity and discharge are much higher than those of streamflows, including catchments similar in size. Sediment transport capacity of lahars is exceptional, owing to buoyancy, dispersive pressure, and to the amount of cohesive clay and silt. However, the finding of recent experimental works indicates that even clay-rich lahar mixtures have little true cohesion. Therefore, the typical classification of lahars into "cohesive" and "non cohesive" seems to be inappropriate at present. Besides, past work on lahar mechanics used models based on the Bagnold's or the Bingham's theories. Recent advances in experimentation show that a lahar has specific rheological properties: it moves as a surge or series of surges, driven by gravity, by porosity fluctuation, and by pore fluid pressures, in accordance with the Coulomb grain flow model. Grain size distribution and sorting control pore pressure distribution. Lahar mechanics depend on much more than steady-state rheology, because lahars are highly unsteady and typically heterogeneous flows. Lahar can show a succession of debris flow phases, hyperconcentrated flow phases, and sometimes transient streamflow phases. Therefore, some fluids-mechanics concepts and terminology, such as "viscous", "laminar" or "non-Newtonian" are inappropriate to describe the mechanical properties of lahars. Processes of deposition are complex and poorly known. Interpretation of massive and unsorted lahar deposits commonly ascribe the deposition regime to a freezing en masse process. However, recent laboratory experiments highlight that debris-flow deposits may result from incremental deposition processes.
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Vera, Pablo, Patricio Ortega, Edwin Casa, Jorge Santamaría und Ximena Hidalgo. „Modelación Numérica y Mapas de Afectación por Flujo de Lahares Primarios en el Drenaje Sur del Volcán Cotopaxi“. Revista Politécnica 43, Nr. 1 (30.04.2019): 61–72. http://dx.doi.org/10.33333/rp.vol43n1.971.
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Los lahares primarios originados durante erupciones de volcanes nevados, como el volcán Cotopaxi, son el resultado de la combinación de mecanismos físicos relacionados con el fenómeno eruptivo como la expulsión de ceniza, material piroclástico y flujos de lava incandescente que provocan el derretimiento súbito de una porción del glaciar. Afectan directamente asentamientos humanos e infraestructura desarrollada a lo largo de los cauces de los ríos y llanuras que corresponden a los drenajes naturales por donde transitan los lahares. El periodo de recurrencia eruptiva del volcán es relativamente amplio considerando la más reciente erupción significativa que ha sido registrada en junio de 1877. La investigación se enfoca en la modelación numérica unidimensional para flujo no permanente realizada en el programa libre HEC-RAS, considerando información geológica, glaciológica, vulcanológica y cartográfica actual, generada y recopilada en campo durante los últimos años. Estos datos han sido analizados y considerados para la definición de los parámetros iniciales que corresponden a volúmenes e hidrogramas. El modelo numérico calibrado en base al evento histórico de 1877, constituye la base para la simulación de los escenarios probables de ocurrencia. Los resultados obtenidos permiten la generación de mapas de afectación referenciales que constituyen un aporte técnico y práctico, ya que pueden ser utilizados para tomar decisiones acerca de la definición de zonas de afectación, sitios seguros, planificación territorial, planes de concientización, recuperación y mitigación ante procesos eruptivos futuros del volcán Cotopaxi que afecten de manera particular el valle de Latacunga.
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Katsova, Maria, Jeremy Drake und Moissei Livshits. „Post-flare Coronal Activity on AU Mic Detected by EUVE“. International Astronomical Union Colloquium 151 (1995): 146–47. http://dx.doi.org/10.1017/s0252921100034886.
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Data of long-duration emission arising after the impulsive rise and decay in a flaring event on the red dwarf star AU Mic are discussed. Intensive EUV emission in the band 65-190 Å was registered by the Extreme Ultraviolet Explorer (EUVE) after both impulses during half a day. A similar behavior of the flux in the Fe XVIII 93.9 Å line is detected after the first powerful impulse. The decay of the intensity in the 65-190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with a typical flare plasma density. Some difficulties with two explanations of this event proposed earlier are discussed. Explanation (i) - the radiation of dense loops at main phase of the flare, and (ii) - the emission of the low-dense plasma of coronal transients (CME). The temporal behavior of the emission measure is determined for both the 65-190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1-2000 Å region for the long-duration event lasting almost 12 hours is 3 · 1035 ergs. The following physical model is proposed to explain the prolonged event (Fig. 1): the source of emission is the system of high coronal loops, the size of which is more than the active region scale, but is less than the stellar radius. The temperature of the plasma in the loops decreases from 107 K slowly, during a few hours. The densities in these loops are in the range 1013 cm−3 to 5 · 109 cm−3. Such systems, when the plasma therein becomes cool, are observed in the Hα line during large solar flares (for instance, June 15, 1991) after CME. Some additional post-flare energy input into this high coronal loop systems can be caused by the reconnection in vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.Apparently, we are faced here with a new kind of surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events on subgiants, which are components of RS CVn binaries.The full version of this contribution will be published in Astronomicheskij Zhurnal (Astronomy Reports), 1995, Vol. 72.
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Delgado Granados, Hugo, und Lillian Martin del Pozzo. „Pliocene to Holocene volcanic geology at the junction of Las Cruces, Chichinautzin and Ajusto ranges, southwest of Mexico City“. Geofísica Internacional 32, Nr. 3 (01.07.1993): 511–22. http://dx.doi.org/10.22201/igeof.00167169p.1993.32.3.526.
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El trabajo está enfocado al estudio de la estratigrafía de una pequeña área volcánica al sur de la ciudad de México, apotando información volcanológica y tratando de respetar la formalidad estratigráfica. Entre el Plioceno Tardío y el Holoceno ocurrieron tres diferentes periodos de colvanismo en la región donde se unen las sierras de Las Cruces, el Ajusco y Chichinautzin. El período más antiguo, denominado Período Aruptivo Las Cruces, está representado por la actividad del volcán poligenético Los Picachos consistente de flujos piroclásicos dacíticos, lahares y lavas de la Formación de Las Cruces (constituído de los dos miembros: Brecha Piroclásica Cantimplora y Lava Dacítica Apilulco), formada principalmente durante el Plioceno Tardío-Pleistoceno Temprano. Durante el Período Eruptivo Ajusto (Pleistoceno Medio), el volcán Ajusco se formó por el emplazamiento de varios domos de lava andesítica. La última etapa eruptiva en la región fue el Periódo Eruptivo Chichinautzin (volcanismo monogenético desarrolladao durante el Pleistoceno Tardío y el Holoceno), de naturaleza estromboliana. Los conos de escoria y de lava que fueron formados en este período, constituyen a las diferentes unidades del Grupo Chichinautzin. Los volcanes Los Picachos, Ajusco, Panza y conos asociados están alineados sobre un sistema de fractura N65° W (activo desde el Plioceno Tardío). Varias fallas normales son paralelas a este alineamiento. Glaciares correspondientes a las glaciaciones Santo Tomás y Albergue dejaron "cuernos", valles en forma de "U", circos y morrenas en los volcanes Los Picachos y Ajusco. El volcanismo del período Eruptivo Chichinautzin fue contemporáneo con un período interglacial durante el Pleistoceno Tardío (entre las glaciaciones Santo Tomás y Albergue).
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Aguilera, Felipe, Oscar Benavente, Francisco Gutiérrez, Jorge Romero, Ornella Saltori, Rodrigo González, Mariano Agusto, Alberto Caselli und Marcela Pizarro. „Eruptive activity of Planchón-Peteroa volcano for period 2010-2011, Southern Andean Volcanic Zone, Chile“. Andean Geology 43, Nr. 1 (30.09.2015): 20. http://dx.doi.org/10.5027/andgeov43n1-a02.
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Planchón-Peteroa volcano started a renewed eruptive period between January 2010 and July 2011. This eruptive period was characterized by the occurrence of 4 explosive eruptive phases, dominated by low-intensity phreatic activity, which produced almost permanent gas/steam columns (200-800 m height over the active crater). Those columns presented frequently scarce ash, and were interrupted by phreatic explosions that produced ash columns 1,000-3,000 m height in the more intense periods. Eruptive plumes were transported in several directions (NW, N, NE, E and SE), but more than half of the time the plume axis was 130-150° E, and reached a distance up to 638 km from the active crater. Tephra fall deposits identified in the NW, N, NE, E and SE flanks covered an area of 1,265 km2, thickness variable from 4 m (SE border of active crater) to ~0.5 cm 36.8 km SE and ~8 km NW from active crater, respectively, corresponding to a minimum volume of 0.0088 km3. Tephra fall deposit is exclusively constituted of no juvenile fragments including: lithics fragments as main component, quartz and plagioclase crystals, some oxidized lithics, and occasional presence of Fe oxide, and less frequently Cu minerals, as single fragments. We present new field-based measurements data of the geochemistry of gas/water from fumaroles and acid crater lakes, and fall deposit analysis, that integrated with the eruptive record and GOES satellite data, suggests that the eruptive period 2010-2011 has been related to an increasing of heat and mass transfer from hydrothermal-magmatic reservoirs, which would have been favoured by the formation and/or reactivation of cracks after 8.8 Mw Maule earthquake in February 2010. This process also allowed the ascent of fluids from a shallow hydrothermal source, dominated by reduced species as H2S and CH4, during the entire eruptive period, and the release of more oxidizing fluids from a deep magmatic reservoir, dominated by acid species as SO2, HCl and HF, increasing strongly after the end of the eruptive period, probably since October 2011. The eruptive period was scored with a magnitude of 3.36, corresponding to a VEI 1-2.
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Romero Ruiz, Carmen, und Esther Beltrán Yanes. „El impacto de las coladas de 1706 en la ciudad de Garachico. (Tenerife, Islas Canarias, España)“. Investigaciones Geográficas, Nr. 63 (15.06.2015): 99. http://dx.doi.org/10.14198/ingeo2015.63.07.
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Uno de los escenarios eruptivos de mayor importancia en Canarias es el asociado al desarrollo de erupciones basálticas fisurales, de comportamiento efusivo y localizadas en sectores de rifts volcánicos de bajas tasas eruptivas. El 80% del volcanismo histórico producido en Canarias se ha localizado en estas estructuras y en el 60% de los casos las coladas se emplazan en ambientes litorales, densamente poblados, lo que las convierte en el riesgo volcánico más importante de las islas. La erupción de Garachico ha sido el fenómeno volcánico histórico de mayor impacto socioeconómico de Tenerife. Entre el 5 de mayo y el 13 de junio de 1706 se emitió 0,045 km3 de materiales volcánicos que cubrieron un área de 7,6 km2. Este trabajo se centra en los daños vinculados al emplazamiento de las coladas en el sector litoral, pues fueron las causantes de las mayores pérdidas provocadas por la erupción. Este estudio evidencia, asimismo, que el desarrollo de erupciones efusivas en rifts de este tipo obliga a contemplar no sólo los escenarios eruptivos más probables sino también los escenarios geográficos de inserción de las erupciones, pues éstos condicionan las modalidades de emplazamiento de los flujos lávicos y los riesgos derivados de ellos.
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Blumthaler, M., und W. Ambach. „Changes in solar radiation fluxes after the Pinatubo eruption“. Tellus B: Chemical and Physical Meteorology 46, Nr. 1 (Januar 1994): 76–78. http://dx.doi.org/10.3402/tellusb.v46i1.15753.
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BLUMTHALER, M., und W. AMBACH. „Changes in solar radiation fluxes after the Pinatubo eruption“. Tellus B 46, Nr. 1 (Februar 1994): 76–78. http://dx.doi.org/10.1034/j.1600-0889.1994.00007.x.
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Mohr, Christian H., Oliver Korup, Héctor Ulloa und Andrés Iroumé. „Pyroclastic Eruption Boosts Organic Carbon Fluxes Into Patagonian Fjords“. Global Biogeochemical Cycles 31, Nr. 11 (November 2017): 1626–38. http://dx.doi.org/10.1002/2017gb005647.
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BARYSHEV, Alexander. „The Oldoynio Lengai volcano, Tanzania: the essence of its recent eruptions“. Domestic geology, Nr. 3-4 (14.09.2021): 60–69. http://dx.doi.org/10.47765/0869-7175-2021-10023.
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The article considers the nature of the volcanic fluxes that are traditionally interpreted as the only example of recent mantle-derived carbonatite lavas (carbonate magmas or melts) on the Earth. However, it turns out that this is not correct. These fluxes represent muddy soda masses with organics. Their source are masses of solutions and sediments of the Natron alkaline lake, that penetrate deep to the above-chamber space of the volcano along riftogenic faults, where they are heated and then erupt as fluxes, geysers, and ash masses. The eruption products in turn get to the lake again. At the recent stage of development, the Oldoynio Lengai volcano represents an epimagmatic phreatic hydrothermal recycling system.
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Sparks, R. S. J., C. Annen, J. D. Blundy, K. V. Cashman, A. C. Rust und M. D. Jackson. „Formation and dynamics of magma reservoirs“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, Nr. 2139 (07.01.2019): 20180019. http://dx.doi.org/10.1098/rsta.2018.0019.
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The emerging concept of a magma reservoir is one in which regions containing melt extend from the source of magma generation to the surface. The reservoir may contain regions of very low fraction intergranular melt, partially molten rock (mush) and melt lenses (or magma chambers) containing high melt fraction eruptible magma, as well as pockets of exsolved magmatic fluids. The various parts of the system may be separated by a sub-solidus rock or be connected and continuous. Magma reservoirs and their wall rocks span a vast array of rheological properties, covering as much as 25 orders of magnitude from high viscosity, sub-solidus crustal rocks to magmatic fluids. Time scales of processes within magma reservoirs range from very slow melt and fluid segregation within mush and magma chambers and deformation of surrounding host rocks to very rapid development of magma and fluid instability, transport and eruption. Developing a comprehensive model of these systems is a grand challenge that will require close collaboration between modellers, geophysicists, geochemists, geologists, volcanologists and petrologists. This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’.
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Madonia, P., F. Grassa, M. Cangemi und C. Musumeci. „Geomorphological and geochemical characterization of the 11 August 2008 mud volcano eruption at S. Barbara village (Sicily, Italy) and its possible relationship with seismic activity“. Natural Hazards and Earth System Sciences 11, Nr. 5 (24.05.2011): 1545–57. http://dx.doi.org/10.5194/nhess-11-1545-2011.
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Abstract. On 11 August 2008 a paroxysmal eruption occurred at Santa Barbara mud volcano (MV), located close to Caltanissetta, one of the most densely populated cities of Sicily (Italy). An associated minor event took place on August 2009. Both the events caused severe damage to civil infrastructures located within a range of about 2 km from the eruptive vent. Geomorphological, geochemical, and seismological investigations were carried out for framing the events in the appropriate geodynamic context. Geomorphological surveys recognized, in the immediate surrounding of the main emission point, two different families of processes and landforms: (i) ground deformations and (ii) changes in morphology and number of the fluid emitting vents. These processes were associated to a wider network of fractures, seemingly generated by the shock wave produced by the gas blast that occurred at the main paroxysm. Geochemical characterization allowed an estimation of the source of the fluids, or at least their last standing, at about 3 km depth. Finally, the close time relationships observed between anomalous increments of seismic activity and the two main paroxysmal events accounted for a possible common trigger for both the phenomena, even with different timing due to the very different initial conditions and characteristics of the two processes, i.e. seismogenesis and gas overloading.
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Upton, Brian G. J., Nic Odling, Linda A. Kirstein, John R. Underhill, Jacek Puziewicz, Theodore Ntaflos, Bogusław Bagiński et al. „The Weaklaw Vent, SE Scotland: Metasomatism of eruptive products by carbo-hydro-fluids of probable mantle origin“. Mineralogical Magazine 83, Nr. 6 (21.10.2019): 855–67. http://dx.doi.org/10.1180/mgm.2019.67.
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AbstractThe Weaklaw vent in SE Scotland (East Lothian coast), inferred to be Namurian, produced lava spatter and volcanic bombs. The latter commonly contained ultramafic xenoliths. All were metasomatised by carbonic fluids rich in incompatible elements. The lavas and xenoliths are inferred to have been basanites and lherzolites prior to metasomatism. The abundance and size of (carbonated) peridotite xenoliths at Weaklaw denotes unusual rapidity of magma ascent and high-energy eruption making Weaklaw exceptional in the British Isles. The lavas and xenoliths were altered subsequently by low-temperature (<200°C) carbo-hydrous fluids to carbonate, clay and quartz assemblages. A small irregular tuffisite ‘dyke’ that transects the ejecta is also composed dominantly of carbonates and clays. The peridotitic xenoliths are typically foliated, interpreted as originating as pre-entrainment mantle shear-planes.Analyses of the relic spinels shows them to be compositionally similar to spinels in local unaltered lherzolites from near-by basanitic occurrences. Chromium showed neither significant loss nor gain but was concentrated in a di-octahedral smectite allied to volkonskoite. It is in the complex association of smectite with other clays, chlorite and possibly fuchsite that the diverse incompatible elements are concentrated.We conclude that late Palaeozoic trans-tensional fault movement caused mantle shearing. Rapid ascent of basanite magma entrained large quantities of sheared lithospheric mantle. This was followed by ascent of an aggressive carbonate-/ hydroxyl-rich fluid causing pervasive metasomatism. The vent is unique in several ways: in its remarkable clay mineralogy and in displaying such high Cr-clays in a continental intra-plate setting; in being more productive in terms of its ‘cargo’ of peridotite xenoliths; in presenting an essentially un-eroded sequence of Namurian extrusives; and, not least, for giving evidence for post-eruptive, surface release of small-melt, deep-source fluids.
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Filippi, Jean-Baptiste, Jonathan Durand, Pierre Tulet und Soline Bielli. „Multiscale Modeling of Convection and Pollutant Transport Associated with Volcanic Eruption and Lava Flow: Application to the April 2007 Eruption of the Piton de la Fournaise (Reunion Island)“. Atmosphere 12, Nr. 4 (17.04.2021): 507. http://dx.doi.org/10.3390/atmos12040507.
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Volcanic eruptions can cause damage to land and people living nearby, generate high concentrations of toxic gases, and also create large plumes that limit observations and the performance of forecasting models that rely on these observations. This study investigates the use of micro- to meso-scale simulation to represent and predict the convection, transport, and deposit of volcanic pollutants. The case under study is the 2007 eruption of the Piton de la Fournaise, simulated using a high-resolution, coupled lava/atmospheric approach (derived from wildfire/atmosphere coupled code) to account for the strong, localized heat and gaseous fluxes occurring near the vent, over the lava flow, and at the lava–sea interface. Higher resolution requires fluxes over the lava flow to be explicitly simulated to account for the induced convection over the flow, local mixing, and dilution. Comparisons with air quality values at local stations show that the simulation is in good agreement with observations in terms of sulfur concentration and dynamics, and performs better than lower resolution simulation with parameterized surface fluxes. In particular, the explicit representation of the thermal flows associated with lava allows the associated thermal breezes to be represented. This local modification of the wind flow strongly impacts the organization of the volcanic convection (injection height) and the regional transport of the sulfur dioxide emitted at the vent. These results show that explicitly solving volcanic activity/atmosphere complex interactions provides realistic forecasts of induced pollution.
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Burton, Mike, Catherine Hayer, Craig Miller und Bruce Christenson. „Insights into the 9 December 2019 eruption of Whakaari/White Island from analysis of TROPOMI SO2 imagery“. Science Advances 7, Nr. 25 (Juni 2021): eabg1218. http://dx.doi.org/10.1126/sciadv.abg1218.
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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.
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Tajima, Yasuhisa, Setsuya Nakada, Fukashi Maeno, Toshio Huruzono, Masaaki Takahashi, Akihiko Inamura, Takeshi Matsushima, Masashi Nagai und Jun Funasaki. „Shallow Magmatic Hydrothermal Eruption in April 2018 on Ebinokogen Ioyama Volcano in Kirishima Volcano Group, Kyushu, Japan“. Geosciences 10, Nr. 5 (14.05.2020): 183. http://dx.doi.org/10.3390/geosciences10050183.
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The Kirishima Volcano Group is a volcanic field ideal for studying the mechanism of steam-driven eruptions because many eruptions of this type occurred in the historical era and geophysical observation networks have been installed in this volcano. We made regular geothermal observations to understand the hydrothermal activity in Ebinokogen Ioyama Volcano. Geothermal activity resumed around the Ioyama from December 2015. A steam blowout occurred in April 2017, and a hydrothermal eruption occurred in April 2018. Geothermal activity had gradually increased before these events, suggesting intrusion of the magmatic component fluids in the hydrothermal system under the volcano. The April 2018 eruption was a magmatic hydrothermal eruption caused by the injection of magmatic fluids into a very-shallow hydrothermal system as a bottom–up fluid pressurization, although juvenile materials were not identifiable. Additionally, the upwelling of mixed magma–meteoric fluids to the surface as a kick was observed just before the eruption to cause the top–down flashing of April 2018. A series of events was generated in the shallower hydrothermal regime consisting of multiple systems divided by conductive caprock layers.
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Hirtl, Marcus, Barbara Scherllin-Pirscher, Martin Stuefer, Delia Arnold, Rocio Baro, Christian Maurer und Marie D. Mulder. „Extension of the WRF-Chem volcanic emission preprocessor to integrate complex source terms and evaluation for different emission scenarios of the Grimsvötn 2011 eruption“. Natural Hazards and Earth System Sciences 20, Nr. 11 (24.11.2020): 3099–115. http://dx.doi.org/10.5194/nhess-20-3099-2020.
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Abstract. Volcanic eruptions may generate volcanic ash and sulfur dioxide (SO2) plumes with strong temporal and vertical variations. When simulating these changing volcanic plumes and the afar dispersion of emissions, it is important to provide the best available information on the temporal and vertical emission distribution during the eruption. The volcanic emission preprocessor of the chemical transport model WRF-Chem has been extended to allow the integration of detailed temporally and vertically resolved input data from volcanic eruptions. The new emission preprocessor is tested and evaluated for the eruption of the Grimsvötn volcano in Iceland 2011. The initial ash plumes of the Grimsvötn eruption differed significantly from the SO2 plumes, posing challenges to simulate plume dynamics within existing modelling environments: observations of the Grimsvötn plumes revealed strong vertical wind shear that led to different transport directions of the respective ash and SO2 clouds. Three source terms, each of them based on different assumptions and observational data, are applied in the model simulations. The emission scenarios range from (i) a simple approach, which assumes constant emission fluxes and a predefined vertical emission profile, to (ii) a more complex approach, which integrates temporarily varying observed plume-top heights and estimated emissions based on them, to (iii) the most complex method that calculates temporal and vertical variability of the emission fluxes based on satellite observations and inversion techniques. Comparisons between model results and independent observations from satellites, lidar, and surface air quality measurements reveal the best performance of the most complex source term.
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Madjarska, Maria S., Duncan H. Mackay, Klaus Galsgaard, Thomas Wiegelmann und Haixia Xie. „Eruptions from coronal bright points: A spectroscopic view by IRIS of a mini-filament eruption, QSL reconnection, and reconnection-driven outflows“. Astronomy & Astrophysics 660 (April 2022): A45. http://dx.doi.org/10.1051/0004-6361/202142439.
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Context. Our study investigates a mini-filament eruption associated with cancelling magnetic fluxes. The eruption originates from a small-scale loop complex commonly known as a coronal bright point (CBP). The event is uniquely recorded in both the imaging and spectroscopic data taken with the Interface Region Imaging Spectrograph (IRIS). Aims. The investigation aims to gain a better understanding of the physical processes driving these ubiquitous small-scale eruptions. Methods. We analysed IRIS spectroscopic and slit-jaw imaging observations as well as images taken in the extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA) and line-of-sight magnetic-field data from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory. As the observations can only indicate the possible physical processes at play, we also employed a non-linear force-free field (NLFFF) relaxation approach based on the HMI magnetogram time series. This allowed us to further investigate the evolution of the magnetic-field structures involved in the eruption process. Results. We identified a strong small-scale brightening as a micro-flare in a CBP, recorded in emission from chromospheric to flaring plasmas. The mini-eruption is manifested via the ejection of hot (CBP loops) and cool (mini-filament) plasma recorded in both the imaging and spectroscopic data. The micro-flare is preceded by the appearance of an elongated bright feature in the IRIS slit-jaw 1400 Å images, located above the polarity inversion line. The micro-flare starts with an IRIS pixel size brightening and propagates bi-directionally along the elongated feature. We detected, in both the spectral and imaging IRIS data and AIA data, strong flows along and at the edges of the elongated feature; we believe that these represent reconnection outflows. Both edges of the elongated feature that wrap around the edges of the erupting MF evolve into a J-type shape, creating a sigmoid appearance. A quasi-separatrix layer (QSL) is identified in the vicinity of the polarity inversion line by computing the squashing factor, Q, in different horizontal planes of the NLFFF model. Conclusions. This CBP spectro-imaging study provides further evidence that CBPs represent downscaled active regions and, as such, they may make a significant contribution to the mass and energy balance of the solar atmosphere. They are the sources of all range of typical active-region features, including magnetic reconnection along QSLs, (mini-)filament eruptions, (micro-)flaring, reconnection outflows, etc. The QSL reconnection site has the same spectral appearance as the so-called explosive events identified by strong blue- and red-shifted emission, thus providing an answer to an outstanding question regarding the true nature of this spectral phenomenon.