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  • 1
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    Online Resource
    Hybrid-Vlasov simulation of auroral proton precipitation in the cusps: Comparison of northward and southward interplanetary magnetic field driving
    EDP Sciences ; 2020
    In:  Journal of Space Weather and Space Climate Vol. 10 ( 2020), p. 51-
    Details
    In: Journal of Space Weather and Space Climate, EDP Sciences, Vol. 10 ( 2020), p. 51-
    Abstract: Particle precipitation is a central aspect of space weather, as it strongly couples the magnetosphere and the ionosphere and can be responsible for radio signal disruption at high latitudes. We present the first hybrid-Vlasov simulations of proton precipitation in the polar cusps. We use two runs from the Vlasiator model to compare cusp proton precipitation fluxes during southward and northward interplanetary magnetic field (IMF) driving. The simulations reproduce well-known features of cusp precipitation, such as a reverse dispersion of precipitating proton energies, with proton energies increasing with increasing geomagnetic latitude under northward IMF driving, and a nonreversed dispersion under southward IMF driving. The cusp is also found more polewards in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the bursty precipitation during southward IMF driving is associated with the transit of flux transfer events in the vicinity of the cusp. In the northward IMF simulation, dual lobe reconnection takes place. As a consequence, in addition to the high-latitude precipitation spot associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere’s lobe reconnection site. The proton velocity distribution functions along the newly closed dayside magnetic field lines exhibit multiple proton beams travelling parallel and antiparallel to the magnetic field direction, which is consistent with previously reported observations with the Cluster spacecraft. In both runs, clear electromagnetic ion cyclotron waves are generated in the cusps and might further increase the calculated precipitating fluxes by scattering protons to the loss cone in the low-altitude cusp. Global kinetic simulations can improve the understanding of space weather by providing a detailed physical description of the entire near-Earth space and its internal couplings.
    Type of Medium: Online Resource
    ISSN: 2115-7251
    URL: Article
    DOI: 10.1051/swsc/2020053
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 2628166-1
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  • 2
    Online Resource
    Online Resource
    Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions
    Copernicus GmbH ; 2019
    In:  Annales Geophysicae Vol. 37, No. 5 ( 2019-09-10), p. 791-806
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 37, No. 5 ( 2019-09-10), p. 791-806
    Abstract: Abstract. Particle precipitation plays a key role in the coupling of the terrestrial magnetosphere and ionosphere by modifying the upper atmospheric conductivity and chemistry, driving field-aligned currents, and producing aurora. Yet quantitative observations of precipitating fluxes are limited, since ground-based instruments can only provide indirect measurements of precipitation, while particle telescopes aboard spacecraft merely enable point-like in situ observations with an inherently coarse time resolution above a given location. Further, orbit timescales generally prevent the analysis of whole events. On the other hand, global magnetospheric simulations can provide estimations of particle precipitation with a global view and higher time resolution. We present the first results of auroral (∼1–30 keV) proton precipitation estimation using the Vlasiator global hybrid-Vlasov model in a noon–midnight meridional plane simulation driven by steady solar wind with a southward interplanetary magnetic field. We first calculate the bounce loss-cone angle value at selected locations in the simulated nightside magnetosphere. Then, using the velocity distribution function representation of the proton population at those selected points, we study the population inside the loss cone. This enables the estimation of differential precipitating number fluxes as would be measured by a particle detector aboard a low-Earth-orbiting (LEO) spacecraft. The obtained differential flux values are in agreement with a well-established empirical model in the midnight sector, as are the integral energy flux and mean precipitating energy. We discuss the time evolution of the precipitation parameters derived in this manner in the global context of nightside magnetospheric activity in this simulation, and we find in particular that precipitation bursts of 〈1 min duration can be self-consistently and unambiguously associated with dipolarising flux bundles generated by tail reconnection. We also find that the transition region seems to partly regulate the transmission of precipitating protons to the inner magnetosphere, suggesting that it has an active role in regulating ionospheric precipitation.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    URL: Article
    DOI: 10.5194/angeo-37-791-2019
    DOI: 10.5194/angeo-37-791-2019-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 1458425-6
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  • 3
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    Online Resource
    Helium in the Earth's foreshock: a global Vlasiator survey
    Copernicus GmbH ; 2020
    In:  Annales Geophysicae Vol. 38, No. 5 ( 2020-10-20), p. 1081-1099
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 38, No. 5 ( 2020-10-20), p. 1081-1099
    Abstract: Abstract. The foreshock is a region of space upstream of the Earth's bow shock extending along the interplanetary magnetic field (IMF). It is permeated by shock-reflected ions and electrons, low-frequency waves, and various plasma transients. We investigate the extent of the He2+ foreshock using Vlasiator, a global hybrid-Vlasov simulation. We perform the first numerical global survey of the helium foreshock and interpret some historical foreshock observations in a global context. The foreshock edge is populated by both proton and helium field-aligned beams, with the proton foreshock extending slightly further into the solar wind than the helium foreshock and both extending well beyond the ultra-low frequency (ULF) wave foreshock. We compare our simulation results with Magnetosphere Multiscale (MMS) Hot Plasma Composition Analyzer (HPCA) measurements, showing how the gradient of suprathermal ion densities at the foreshock crossing can vary between events. Our analysis suggests that the IMF cone angle and the associated shock obliquity gradient can play a role in explaining this differing behaviour. We also investigate wave–ion interactions with wavelet analysis and show that the dynamics and heating of He2+ must result from proton-driven ULF waves. Enhancements in ion agyrotropy are found in relation to, for example, the ion foreshock boundary, the ULF foreshock boundary, and specular reflection of ions at the bow shock. We show that specular reflection can describe many of the foreshock ion velocity distribution function (VDF) enhancements. Wave–wave interactions deep in the foreshock cause de-coherence of wavefronts, allowing He2+ to be scattered less than protons.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-38-1081-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 1458425-6
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  • 4
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    Online Resource
    Foreshock cavitons and spontaneous hot flow anomalies: a statistical study with a global hybrid-Vlasov simulation
    Copernicus GmbH ; 2021
    In:  Annales Geophysicae Vol. 39, No. 5 ( 2021-10-14), p. 911-928
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 39, No. 5 ( 2021-10-14), p. 911-928
    Abstract: Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low-frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which are thought to evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward–southward angle of 45∘, continuous formation of cavitons is found up to ∼11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ∼2 RE from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-39-911-2021
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 1458425-6
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  • 5
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    Video5.MP4
    Frontiers Media SA ; 2022
    In:  Frontiers in Astronomy and Space Sciences Vol. 9 ( 2022-9-2)
    Details
    In: Frontiers in Astronomy and Space Sciences, Frontiers Media SA, Vol. 9 ( 2022-9-2)
    Abstract: Ultra-low frequency (ULF) waves are routinely observed in Earth’s dayside magnetosphere. Here we investigate the influence of externally-driven density variations in the near-Earth space in the ULF regime using global 2D simulations performed with the hybrid-Vlasov model Vlasiator. With the new time-varying boundary setup, we introduce a monochromatic Pc5 range periodic density variation in the solar wind. A breathing motion of the magnetopause and changes in the bow shock standoff position are caused by the density variation, the time lag between which is found to be consistent with propagation at fast magnetohydrodynamic speed. The oscillations also create large-scale stripes of variations in the magnetosheath and modulate the mirror and electromagnetic ion cyclotron modes. We characterize the spatial-temporal properties of ULF waves at different phases of the variation. Less prominent EMIC and mirror mode wave activities near the center of magnetosheath are observed with decreasing upstream Mach number. The EMIC wave occurrence is strongly related to pressure anisotropy and β ‖ , both vary as a function of the upstream conditions, whereas the mirror mode occurrence is highly influenced by fast waves generated from upstream density variations.
    Type of Medium: Online Resource
    ISSN: 2296-987X
    URL: Article
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    DOI: 10.3389/fspas.2022.984918
    DOI: 10.3389/fspas.2022.984918.s001
    DOI: 10.3389/fspas.2022.984918.s002
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    DOI: 10.3389/fspas.2022.984918.s012
    DOI: 10.3389/fspas.2022.984918.s013
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2778829-5
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  • 6
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    Online Resource
    DataSheet1.PDF
    Frontiers Media SA ; 2022
    In:  Frontiers in Astronomy and Space Sciences Vol. 9 ( 2022-9-29)
    Details
    In: Frontiers in Astronomy and Space Sciences, Frontiers Media SA, Vol. 9 ( 2022-9-29)
    Abstract: Ultra-low frequency (ULF) waves in the Pc3 range, with periods between 10–45 s, are routinely observed in Earth’s dayside magnetosphere. They are thought to originate in the foreshock, which extends upstream of the quasi-parallel bow shock and is populated with shock-reflected particles. The foreshock is permeated with ULF waves generated by ion beam instabilities, most notably the “30-s” waves whose periods match those of the Pc3 waves and which are carried earthward by the solar wind flow. However, the global picture of Pc3 wave activity from the foreshock to the magnetosphere and its response to changing solar wind conditions is still poorly understood. In this study, we investigate the global distribution and properties of Pc3 waves across near-Earth space using global simulations performed with the hybrid-Vlasov model Vlasiator. The simulations enable us to study the waves in their global context, and compare their properties in the foreshock, magnetosheath and dayside magnetosphere, for different sets of upstream solar wind conditions. We find that in all three regions the Pc3 wave power peaks at higher frequencies when the interplanetary magnetic field (IMF) strength is larger, consistent with previous studies. The Pc3 wave power is significantly enhanced in all three regions for higher solar wind Alfvén Mach number. As this parameter is known to affect the shock properties but has little impact inside the magnetosphere, this brings further support to the magnetospheric waves originating in the foreshock. Other parameters that are found to influence the foreshock wave power are the solar wind density and the IMF cone angle. Inside the magnetosphere, the wave power distribution depends strongly on the IMF orientation, which controls the foreshock position upstream of the bow shock. The wave power is largest when the angle between the IMF and the Sun-Earth line is smallest, suggesting that wave generation and transmission are most efficient in these conditions.
    Type of Medium: Online Resource
    ISSN: 2296-987X
    URL: Article
    URL: Article
    DOI: 10.3389/fspas.2022.989369
    DOI: 10.3389/fspas.2022.989369.s001
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2778829-5
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  • 7
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    Online Resource
    First 3D hybrid-Vlasov global simulation of auroral proton precipitation and comparison with satellite observations
    EDP Sciences ; 2023
    In:  Journal of Space Weather and Space Climate Vol. 13 ( 2023), p. 20-
    Details
    In: Journal of Space Weather and Space Climate, EDP Sciences, Vol. 13 ( 2023), p. 20-
    Abstract: The precipitation of charged particles from the magnetosphere into the ionosphere is one of the crucial coupling mechanisms between these two regions of geospace and is associated with multiple space weather effects, such as global navigation satellite system signal disruption and geomagnetically induced currents at ground level. While precipitating particle fluxes have been measured by numerous spacecraft missions over the past decades, it often remains difficult to obtain global precipitation patterns with a good time resolution during a substorm. Numerical simulations can help to bridge this gap and improve the understanding of mechanisms leading to particle precipitation at high latitudes through the global view they offer on the near-Earth space system. We present the first results on auroral (0.5–50 keV) proton precipitation within a 3-dimensional simulation of the Vlasiator hybrid-Vlasov model. The run is driven by southward interplanetary magnetic field conditions with constant solar wind parameters. We find that on the dayside, cusp proton precipitation exhibits the expected energy–latitude dispersion and takes place in the form of successive bursts associated with the transit of flux transfer events formed through dayside magnetopause reconnection. On the nightside, the precipitation takes place within the expected range of geomagnetic latitudes, and it appears clearly that the precipitating particle injection is taking place within a narrow magnetic local time span, associated with fast Earthward plasma flows in the near-Earth magnetotail. Finally, the simulated precipitating fluxes are compared to observations from Defense Meteorological Satellite Program spacecraft during driving conditions similar to those in the simulation and are found to be in good agreement with the measurements.
    Type of Medium: Online Resource
    ISSN: 2115-7251
    URL: Article
    DOI: 10.1051/swsc/2023017
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 2628166-1
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  • 8
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    Magnetotail plasma eruptions driven by magnetic reconnection and kinetic instabilities
    Springer Science and Business Media LLC ; 2023
    In:  Nature Geoscience Vol. 16, No. 7 ( 2023-07), p. 570-576
    Details
    In: Nature Geoscience, Springer Science and Business Media LLC, Vol. 16, No. 7 ( 2023-07), p. 570-576
    Abstract: Rapid plasma eruptions explosively release energy within Earth’s magnetosphere, at the Sun and at other planets. At Earth, these eruptions, termed plasmoids, occur in the magnetospheric nightside and are associated with sudden brightening of the aurora. The chain of events leading to the plasmoid is one of the longest-standing unresolved questions in space physics. Two competing paradigms have been proposed to explain the course of events. The first asserts that magnetic reconnection changes the magnetic topology in the tail, severing a part of the magnetosphere as plasmoid. The second employs kinetic instabilities that first disrupt the current sheet supporting the magnetotail and launch waves that trigger the topological change to eject the plasmoid. Here we numerically simulate Earth’s magnetosphere at realistic scales using a model that captures the physics underlying both paradigms. We show that both magnetic reconnection and kinetic instabilities are required to induce a global topological reconfiguration of the magnetotail, thereby combining the seemingly contradictory paradigms. Our results help to understand how plasma eruptions may take place, guide spacecraft constellation mission design to capture these ejections in observations and lead to improved understanding of space weather by improving the predictability of the plasmoids.
    Type of Medium: Online Resource
    ISSN: 1752-0894 , 1752-0908
    URL: Article
    DOI: 10.1038/s41561-023-01206-2
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2396648-8
    detail.hit.zdb_id: 2405323-5
    SSG: 16,13
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  • 9
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    Enabling technology for global 3D + 3V hybrid-Vlasov simulations of near-Earth space
    AIP Publishing ; 2023
    In:  Physics of Plasmas Vol. 30, No. 4 ( 2023-04-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 30, No. 4 ( 2023-04-01)
    Abstract: We present methods and algorithms that allow the Vlasiator code to run global, three-dimensional hybrid-Vlasov simulations of Earth's entire magnetosphere. The key ingredients that make Vlasov simulations at magnetospheric scales possible are the sparse velocity space implementation and spatial adaptive mesh refinement. We outline the algorithmic improvement of the semi-Lagrangian solver for six-dimensional phase space quantities, discuss the coupling of Vlasov and Maxwell equations' solvers in a refined mesh, and provide performance figures from simulation test runs that demonstrate the scalability of this simulation system to full magnetospheric runs.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/5.0134387
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 1472746-8
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  • 10
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    Resolution dependence of magnetosheath waves in global hybrid-Vlasov simulations
    Copernicus GmbH ; 2020
    In:  Annales Geophysicae Vol. 38, No. 6 ( 2020-12-21), p. 1283-1298
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 38, No. 6 ( 2020-12-21), p. 1283-1298
    Abstract: Abstract. Kinetically driven plasma waves are fundamental for a description of the thermodynamical properties of the Earth's magnetosheath. The most commonly observed ion-scale instabilities are generated by temperature anisotropy of the ions, such as the mirror and proton cyclotron instabilities. We investigate here the spatial resolution dependence of the mirror and proton cyclotron instabilities in a global hybrid-Vlasov simulation using the Vlasiator model; we do this in order to find optimal resolutions and help future global hybrid-Vlasov simulations to save resources when investigating those instabilities in the magnetosheath. We compare the proton velocity distribution functions, power spectra and growth rates of the instabilities in a set of simulations with three different spatial resolutions but otherwise identical set-up. We find that the proton cyclotron instability is absent at the lowest resolution and that only the mirror instability remains, which leads to an increased temperature anisotropy in the simulation. We conclude that the proton cyclotron instability, its saturation and the reduction of the anisotropy to marginal levels are resolved at the highest spatial resolution. A further increase in resolution does not lead to a better description of the instability to an extent that would justify this increase at the cost of numerical resources in future simulations. We also find that spatial resolutions between 1.32 and 2.64 times the inertial length in the solar wind present acceptable limits for the resolution within which the velocity distribution functions resulting from the proton cyclotron instability are still bi-Maxwellian and reach marginal stability levels. Our results allow us to determine a range of spatial resolutions suitable for the modelling of the proton cyclotron and mirror instabilities and should be taken into consideration regarding the optimal grid spacing for the modelling of these two instabilities, within available computational resources.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-38-1283-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 1458425-6
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