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Meteor science contributes greatly to the study of the Solar System and the Earth's atmosphere. However, despite its importance and very long history, meteor science still has a lot to explore in the domain of meteor plasma microphysics and the meteor–ionosphere interaction. Meteors are actually a difficult target for high‐-resolution observations, which leads to the need for more ambitious interdisciplinary observational setups and campaigns. We describe some recent developments in the physics of meteor flight and microphysics of meteor plasma and argue that meteor science should be fully integrated into the science cases of large astronomical facilities. © 2020, Geographical Institute "Jovan Cviji" of the Serbian Academy of Sciences and Arts. All rights reserved. ; 654208 ; Academy of Finland: 325806 ; Russian Foundation for Basic Research, RFBR: 18-08-00074, 19-05-00028 ; Government Council on Grants, Russian Federation ; The authors acknowledge COST Actions BigSkyEarth and Electronet for providing a podium for collaboration and discussion of scientific ideas. This work was supported, in part, by the Academy of Finland project no. 325806 (PlanetS). Research at the Ural Federal University is supported by the Russian Foundation for Basic Research, project nos. 18-08-00074 and 19-05-00028 and the Act 211 of the Government of the Russian Federation, agreement No. 02.A03.21.0006. The authors would also like to thank EUPLANET for supporting this work within the project of European Union's Horizon 2020 research and innovation program under grant No. 654208.

Meteoroids impacting the Earth atmosphere are commonly classified using the PE criterion. This criterion was introduced to support the identification of the fireball type by empirically linking its orbital origin and composition characteristics. Additionally, it is used as an indicator of the meteoroid tensile strength and its ability to penetrate the atmosphere. However, the level of classification accuracy of the PE criterion depends on the ability to constrain the value of the input data, retrieved from the fireball observation, required to derive the PE value. To overcome these uncertainties and achieve a greater classification detail, we propose a new formulation using scaling laws and dimensionless variables that groups all the input variables into two parameters that are directly obtained from the fireball observations. These two parameters, α and β, represent the drag and the mass-loss rates along the luminous part of the trajectory, respectively, and are linked to the shape, strength, ablation efficiency, mineralogical nature of the projectile, and duration of the fireball. Thus, the new formulation relies on a physical basis. This work shows the mathematical equivalence between the PE criterion and the logarithm of 2αβ under the same PE criterion assumptions. We demonstrate that log(2αβ) offers a more general formulation that does not require any preliminary constraint on the meteor flight scenario and discuss the suitability of the new formulation for expanding the classification beyond fully disintegrating fireballs to larger impactors including meteorite-dropping fireballs. The reliability of the new formulation is validated using the Prairie Network meteor observations. ; MM-I acknowledges the support of Aistech Space S.L. MG acknowledges the Academy of Finland project no. 325806 (PlanetS). Research at the Ural Federal University is supported by the Russian Foundation for Basic Research, project nos 18–08-00074 and 19– 05-00028 and the Act 211 of the Government of the Russian Federation, agreement no. 02.A03.21.0006. JMT-R acknowledges the support of MEC under AYA research grant PGC2018–097374-B-I00. The authors sincerely thank the reviewers for their valuable feedback that helped us to improve the paper.

We numerically model the instability of viscous incompressible fluid flows caused by torsional oscillations of the inner sphere in a thin spherical layer with respect to the state of rest. We show that an increase in the frequency of torsional oscillations leads to a change in the mode of the instability, with a transition from secondary flows in the form of Taylor vortices to the structures, which were not previously observed. The revealed instability is found in the frequency range from 0.61 to 2.45 Hz or, if the wavelengths are taken relative to the layer thickness, from 0.67 to 1.33. © Published under licence by IOP Publishing Ltd. ; This work was supported by the Russian Foundation for Basic Research project No. 16-05-00004 and 18-08-00074. MG acknowledges, in part, support from the ERC Advanced Grant No. 320773. Research at the Ural Federal University is supported by the Act 211 of the Government of the Russian Federation, agreement No 02.A03.21.0006. We thank Dr. Laura K. Zschaechner (University of Helsinki, Finnish Center for Astronomy with ESO) for her help with language corrections.

Unsteady viscous incompressible flows in a spherical layer due to an increase in the rotation velocity of the inner sphere with constant acceleration are investigated. The acceleration starts at the Reynolds numbers Re corresponding to a stationary flow and ends at Re higher than the stability limit of the stationary flow, whereupon the rotation velocity of the inner sphere remains constant. The outer sphere is fixed and the spherical layer thickness is equal to the inner sphere radius. The inner sphere acceleration effect is studied on both the formation of one of two possible secondary-flow structures after the acceleration has been stopped, namely, traveling azimuthal waves with wavenumbers of 3 or 4, and on the change in the flow structure during the action of the acceleration. It is shown that not only an increase in the acceleration but also a decrease in Re corresponding to the acceleration onset can lead to an increase in the deviation of the instantaneous velocity profiles from their stationary values and can be accompanied by a variation in the secondary flow wavenumber. © Published under licence by IOP Publishing Ltd. ; This work was supported by the Russian Foundation for Basic Research Project No. 16-05-00004 and 18-08-00074. MG acknowledges,in part, support from the ERC Advanced Grant No. 320773. Research at the Ural Federal University is supported by the Act 211 of the Government of the Russian Federation, agreement No 02.A03.21.0006.

The disruption of asteroids and comets produces cm-sized meteoroids that end up impacting the Earth's atmosphere and producing bright fireballs that might have associated shock waves or, in geometrically favourable occasions excavate craters that put them into unexpected hazardous scenarios. The astrometric reduction of meteors and fireballs to infer their atmospheric trajectories and heliocentric orbits involves a complex and tedious process that generally requires many manual tasks. To streamline the process, we present a software package called SPMN 3D Fireball Trajectory and Orbit Calculator (3D-firetoc), an automatic Python code for detection, trajectory reconstruction of meteors, and heliocentric orbit computation from video recordings. The automatic 3D-firetoc package comprises of a user interface and a graphic engine that generates a realistic 3D representation model, which allows users to easily check the geometric consistency of the results and facilitates scientific content production for dissemination. The software automatically detects meteors from digital systems, completes the astrometric measurements, performs photometry, computes the meteor atmospheric trajectory, calculates the velocity curve, and obtains the radiant and the heliocentric orbit, all in all quantifying the error measurements in each step. The software applies corrections such as light aberration, refraction, zenith attraction, diurnal aberration, and atmospheric extinction. It also characterizes the atmospheric flight and consequently determines fireball fates by using the α - β criterion that analyses the ability of a fireball to penetrate deep into the atmosphere and produce meteorites. We demonstrate the performance of the software by analysing two bright fireballs recorded by the Spanish Fireball and Meteorite Network (SPMN). © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. ; JMT-R, EPA, and AR acknowledge financial support from the SpanishMinistry (PGC2018-097374-B-I00 funded byMCI-AEI-FEDER, PI: JMT-R; CTQ2017-89132-P, PI: AR). MG acknowledges support from the Academy of Finland project no. 325806, and the Russian Foundation for Basic Research, project nos. 18-08-00074 and 19-05-00028. AR is indebted to the 'Ramon y Cajal' program and DIUE (project 2017SGR1323). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 865657) for the project 'Quantum Chemistry on Interstellar Grains' (QUANTUMGRAIN). We thank Prof. Jose A. Docobo and Dr. Pedro P. Campo for the video obtained to exemplify the software (Figs 1-3) recorded from Observatorio Astronomico Ramon Maria Aller (OARMA), Universidad de Santiago de Compostela.

Meteoroids impacting the Earth atmosphere are commonly classified using the PE criterion. This criterion was introduced to support the identification of the fireball type by empirically linking its orbital origin and composition characteristics. Additionally, it is used as an indicator of the meteoroid tensile strength and its ability to penetrate the atmosphere. However, the level of classification accuracy of the PE criterion depends on the ability to constrain the value of the input data, retrieved from the fireball observation, required to derive the PE value. To overcome these uncertainties and achieve a greater classification detail, we propose a new formulation using scaling laws and dimensionless variables that groups all the input variables into two parameters that are directly obtained from the fireball observations. These two parameters, α and β, represent the drag and the mass-loss rates along the luminous part of the trajectory, respectively, and are linked to the shape, strength, ablation efficiency, mineralogical nature of the projectile, and duration of the fireball. Thus, the new formulation relies on a physical basis. This work shows the mathematical equivalence between the PE criterion and the logarithm of 2αβ under the same PE criterion assumptions. We demonstrate that log(2αβ) offers a more general formulation that does not require any preliminary constraint on the meteor flight scenario and discuss the suitability of the new formulation for expanding the classification beyond fully disintegrating fireballs to larger impactors including meteorite-dropping fireballs. The reliability of the new formulation is validated using the Prairie Network meteor observations. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society ; MM-I acknowledges the support of Aistech Space S.L. MG acknowledges the Academy of Finland project no. 325806 (PlanetS). Research at the Ural Federal University is supported by the Russian Foundation for Basic Research, project nos 18–08-00074 and 19– 05-00028 and the Act 211 of the Government of the Russian Federation, agreement no. 02.A03.21.0006. JMT-R acknowledges the support of MEC under AYA research grant PGC2018–097374-B-I00. The authors sincerely thank the reviewers for their valuable feedback that helped us to improve the paper.

Knowing the optical properties of a sample is important in many scientific fields, such as space science, climate studies, and medicine. In many of these applications, the samples are fragile, unique or available in limited quantities, and have to be subsequently studied by additional techniques, implying that sample preservation is important. Established light scattering single particle measurements involve attaching the sample to a holder or measuring a laminar flow of particles, neither of which allows a controlled, unperturbed non-destructive measurement. Acoustic levitation is a state-of-the-art and non-contacting approach capable of assisting light scattering measurements. However, a full 4π measurement (i.e., a measurement from any direction on the full 4π solid angle) has hither been impossible due to levitation instabilities. Here we present and describe the instrument capable of performing a full 4π light scattering measurement. We measure light scattering properties of millimeter-sized samples at any direction. This is enabled by introducing a novel non-contacting sample holder based on acoustic levitation, which allows a disturbance-free measurement of an orientation-controlled sample. The instrument is scalable and currently employs polarized visible light (400–700 nm). It also measures beam and sample stability as well as temperature and humidity, to ensure consistency of measurements. We demonstrate the 4π capabilities of the instrument by measuring an angular map of light scattering from a polystyrene foam sample, as well as a multi-angular measurement (two semicircular measurements 90° apart) of a sample consisting of agglomerated 500 nm silica spheres. The upper left 2 × 2 submatrix of the Mueller matrix is measured from the sample along the (polar) scattering angle in semi-circular sweeps, changing the azimuthal scattering angle for each sweep. Our results allow for verification of theoretical models by mimicking the conditions of the simulations and by making the measurements directly comparable to model predictions. © 2020 ; Academy of Finland: 325806, 325805 ; European Research Council, ERC: 320773 ; Government Council on Grants, Russian Federation ; Svenska Kulturfonden ; The research leading to these results has received funding from the ERC Advanced Grant 320773 entitled "Scattering and Absorption of Electromagnetic Waves in Particulate Media" (SAEMPL). GM acknowledges Svenska Kulturfonden research grant for doctoral studies. Research by KM, AP, and MG supported, in part, by Academy of Finland projects No. 325805 and 325806. Research at the Ural Federal University is supported by the Act 211 of the Government of the Russian Federation, agreement No. 02.A03.21.0006.

We studied the interior and the fusion crust of the recently recovered Ozerki L6 meteorite using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy, X-ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The phase composition of the interior and of the fusion crust was determined by means of SEM, XRD, and Mössbauer spectroscopy. The unit cell parameters for silicate crystals were evaluated from the X-ray diffractograms and were found the same for the interior and the fusion crust. Magnetization measurements revealed a decrease of the saturation magnetic moment in the fusion crust due to a decrease of Fe-Ni-Co alloy content. Both XRD and Mössbauer spectroscopy show the presence of magnesioferrite in the fusion crust. The temperatures of cation equilibrium distribution between the M1 and M2 sites in silicates calculated using the data obtained from XRD and Mössbauer spectroscopy appeared to be in a good consistency: 553 and 479 K for olivine and 1213 and 1202 K for orthopyroxene. © The Meteoritical Society, 2019. ; Academy of Finland: 325806 ; Russian Foundation for Basic Research, RFBR: 18‐08‐00074, 19‐05‐00028 ; Government Council on Grants, Russian Federation: 02. ; Ministry of Science and Higher Education of the Russian Federation: 3.1959.2017/4.6 ; The authors are grateful to Dr. A. J. Timothy Jull for his useful remarks and comments which helped us to improve the manuscript. This work was supported by the Ministry of Science and Higher Education of the Russian Federation, the Project № 3.1959.2017/4.6 and by Act 211 of the Government of the Russian Federation, agreement № 02.A03.21.0006. M.G. acknowledges the Academy of Finland, project № 325806 (PlanetS) and the Russian Foundation for Basic Research, projects №s 18‐08‐00074 and 19‐05‐00028.

Tsunamis are unpredictable and infrequent but potentially large impact natural disasters. To prepare, mitigate and prevent losses from tsunamis, probabilistic hazard and risk analysis methods have been developed and have proved useful. However, large gaps and uncertainties still exist and many steps in the assessment methods lack information, theoretical foundation, or commonly accepted methods. Moreover, applied methods have very different levels of maturity, from already advanced probabilistic tsunami hazard analysis for earthquake sources, to less mature probabilistic risk analysis. In this review we give an overview of the current state of probabilistic tsunami hazard and risk analysis. Identifying research gaps, we offer suggestions for future research directions. An extensive literature list allows for branching into diverse aspects of this scientific approach. © Copyright © 2021 Behrens, Løvholt, Jalayer, Lorito, Salgado-Gálvez, Sørensen, Abadie, Aguirre-Ayerbe, Aniel-Quiroga, Babeyko, Baiguera, Basili, Belliazzi, Grezio, Johnson, Murphy, Paris, Rafliana, De Risi, Rossetto, Selva, Taroni, Del Zoppo, Armigliato, Bureš, Cech, Cecioni, Christodoulides, Davies, Dias, Bayraktar, González, Gritsevich, Guillas, Harbitz, Kânoǧlu, Macías, Papadopoulos, Polet, Romano, Salamon, Scala, Stepinac, Tappin, Thio, Tonini, Triantafyllou, Ulrich, Varini, Volpe and Vyhmeister. ; This article is based upon work from COST Action CA18109 AGITHAR, supported by COST (European Cooperation in Science and Technology). VB and PC obtained support through the VES20 Inter-Cost LTC 20020 project. MS-G obtained support through the Severo Ochoa Centers of Excellence Program (Ref. CEX 2018–000797-S). TU acknowledges funding from the European Union's Horizon 2020 research and innovation program (ChEESE project, Grant Agreement No. 823844).