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C T Russell - One of the best experts on this subject based on the ideXlab platform.
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ion cyclotron wave generation by planetary ion pickup
Journal of Atmospheric and Solar-Terrestrial Physics, 2007Co-Authors: C T Russell, X BlancocanoAbstract:Ion-cyclotron waves play important roles in planetary Magnetospheres and are diagnostic of the processes operating in the Magnetosphere and of the composition of the plasma producing the waves. At Jupiter, Io's exosphere interacts with the corotating magnetospheric plasma. At Saturn, the neutral torus around the E ring interacts with the corotating plasma. At the unmagnetized planets, Mars and Venus, the interaction is between the solar-wind flow and the planetary exosphere. A possible analog of these processes exists in the vicinity of the Earth's polar cusp where the shocked solar-wind plasma penetrates the Earth's exosphere.
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modeling the size and shape of saturn s magnetopause with variable dynamic pressure
Journal of Geophysical Research, 2006Co-Authors: Chris S. Arridge, KK Kamal K Khurana, NA Achilleos, M. K. Dougherty, C T RussellAbstract:[1] The location and shape of a planetary magnetopause is principally determined by the dynamic pressure, Dp, of the solar wind, the orientation of the planet's magnetic dipole with respect to the solar wind flow, and by the distribution of stresses inside the Magnetosphere. The Magnetospheres of Saturn and Jupiter have strong internal plasma sources compared to the solar wind source and also rotate rapidly, causing an equatorial inflation of the Magnetosphere and consequently the magnetopause. Empirical studies using Voyager and Pioneer data concluded that the kronian magnetopause was Earth-like in terms of its dynamics (Slavin et al., 1985) as revealed by how the position of the magnetopause varies with dynamic pressure. In this paper we present a new pressure-dependent model of Saturn's magnetopause, using the functional form proposed by Shue et al. (1997). To establish the pressure-dependence, we also use a new technique for fitting a pressure-dependent model in the absence of simultaneous upstream pressure measurements. Using a Newtonian form of the pressure balance across the magnetopause boundary and using model rather than minimum variance normals, we estimate the solar wind dynamic pressure at each crossing. By iteratively fitting our model to magnetopause crossings observed by the Cassini and Voyager spacecraft, in parallel with the pressure balance, we obtain a model which is self-consistent with the dynamic pressure estimates obtained. We find a model whose size varies as ∼Dp−1/4.3 and whose flaring decreases with increasing dynamic pressure. This is interpreted in terms of a different distribution of fields and particles stresses which has more in common with the jovian Magnetosphere compared with the terrestrial situation. We compare our model with the existing models of the magnetopause and highlight the very different geometries. We find our results are consistent with recent MHD modeling of Saturn's Magnetosphere (Hansen et al., 2005).
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new horizons in planetary Magnetospheres
Advances in Space Research, 2006Co-Authors: C T RussellAbstract:Abstract The Magnetospheres of Mercury, the Earth and Jupiter provide an especially good comparison of the processes that control the behavior of Magnetospheres. The Mercurian Magnetosphere is the smallest. Its field lines are anchored in the electrically conducting interior of Mercury and not in a conducting ionosphere. The Earth’s Magnetosphere is over an order of magnitude larger than Mercury’s and its ionosphere is dynamically important. Also significant are that synchronous orbit occurs relatively far out in the Magnetosphere and that the solar wind is responsible for the energization of processes therein. Jupiter’s Magnetosphere is another two orders of magnitude larger. Its synchronous orbit, where gravity and centrifugal force balance, lies deep inside the Magnetosphere, about 2% of the way to the magnetopause. Most importantly the jovian Magnetosphere has a strong source of ions deep in the Magnetosphere, but well outside of synchronous orbit, that are accelerated to high velocities. The energy of these accelerated ions and their centrifugal force are sufficient to drastically alter the behavior of the jovian Magnetosphere so that it behaves much differently than the terrestrial Magnetosphere. In this review, we examine what we know about each of these Magnetospheres in the areas in which their contrasts reveal the underlying controlling factors of magnetospheric behavior.
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new horizons in planetary Magnetospheres
cosp, 2004Co-Authors: C T RussellAbstract:The Magnetospheres of Mercury, the Earth and Jupiter provide an especially good comparison of the processes that control the behavior of Magnetospheres. The Mercurian Magnetosphere is the smallest. Its field lines are anchored in the electrically conducting interior of Mercury and not in a conducting ionosphere. The Earths Magnetosphere is over an order of magnitude larger than Mercurys and its ionosphere is dynamically important. Also significant are that synchronous orbit occurs relatively far out in the Magnetosphere and that the solar wind is responsible for the energization of processes therein. Jupiters Magnetosphere is another two orders of magnitude larger. Its synchronous orbit, where gravity and centrifugal force balance, lies deep inside the Magnetosphere, about 2% of the way to the magnetopause. Most importantly the jovian Magnetosphere has a strong source of ions deep in the Magnetosphere, but well outside of synchronous orbit, that are accelerated to high velocities. The energy of these accelerated ions and their centrifugal force are sufficient to drastically alter the behavior of the jovian Magnetosphere so that it behaves much differently than the terrestrial Magnetosphere. In this review, we examine what we know about each of these Magnetospheres in the areas in which their contrasts reveal the underlying controlling factors of magnetospheric behavior. 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.
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outer planet Magnetospheres a tutorial
Advances in Space Research, 2004Co-Authors: C T RussellAbstract:Outer planetary Magnetospheres represent giant laboratories for testing our ideas of how Magnetospheres behave. In this tutorial review we examine the role of external and internal pressure in determining the size and shape of the Magnetosphere. We examine the relative roles of reconnection with the solar wind magnetic field and the mass addition inside the Magnetosphere in driving the circulation of plasma in the Magnetosphere. We also examine how the jovian Magnetosphere maintains a steady state in an average sense despite the continued addition of mass deep in the Magnetosphere. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.
Anatoly Spitkovsky - One of the best experts on this subject based on the ideXlab platform.
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particle acceleration in axisymmetric pulsar current sheets
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Benoit Cerutti, Alexander A Philippov, Kyle Parfrey, Anatoly SpitkovskyAbstract:The equatorial current sheet in pulsar Magnetospheres is often regarded as an ideal site for particle acceleration via relativistic reconnection. Using 2D spherical particle-in-cell simulations, we investigate particle acceleration in the axisymmetric pulsar Magnetosphere as a function of the injected plasma multiplicity and magnetization. We observe a clear transition from a highly charge-separated Magnetosphere for low plasma injection with little current and spin-down power, to a nearly force-free solution for high plasma multiplicity characterized by a prominent equatorial current sheet and high spin-down power. We find significant magnetic dissipation in the current sheet, up to 30% within 5 light-cylinder radii in the high-multiplicity regime. The simulations unambiguously demonstrate that the dissipated Poynting flux is efficiently channeled to the particles in the sheet, close to the Y-point within about 1-2 light cylinder radii from the star. The mean particle energy in the sheet is given by the upstream plasma magnetization at the light cylinder. The study of particle orbits shows that all energetic particles originate from the boundary layer between the open and the closed field lines. Energetic positrons always stream outward, while high-energy electrons precipitate back towards the star through the sheet and along the separatrices, which may result in auroral-like emission. Our results suggest that the current sheet and the separatrices may be the main source of high-energy radiation in young pulsars.
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time dependent 3d magnetohydrodynamic pulsar Magnetospheres oblique rotators
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: Alexander Tchekhovskoy, Anatoly SpitkovskyAbstract:The current state of the art in pulsar Magnetosphere modeling assumes the force-free limit of magnetospheric plasma. This limit retains only partial information about plasma velocity and neglects plasma inertia and temperature. We carried out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of oblique pulsar Magnetospheres that improve upon force-free by retaining the full plasma velocity information and capturing plasma heating in strong current layers. We find rather low levels of magnetospheric dissipation, with less than 10% of pulsar spindown energy dissipated within a few light cylinder radii, and the MHD spindown that is consistent with that in force-free. While oblique Magnetospheres are qualitatively similar to the rotating split-monopole force-free solution at large radii, we find substantial quantitative differences with the split-monopole, e.g., the luminosity of the pulsar wind is more equatorially concentrated than the split-monopole at high obliquities, and the flow velocity is modified by the emergence of reconnection flow directed into the current sheet.
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resistive solutions for pulsar Magnetospheres
The Astrophysical Journal, 2012Co-Authors: Anatoly Spitkovsky, Alexander TchekhovskoyAbstract:The current state of the art in the modeling of pulsar Magnetospheres invokes either the vacuum or force-free limits for the magnetospheric plasma. Neither of these limits can simultaneously account for both the plasma currents and the accelerating electric fields that are needed to explain the morphology and spectra of high-energy emission from pulsars. To better understand the structure of such Magnetospheres, we combine accelerating fields and force-free solutions by considering models of Magnetospheres filled with resistive plasma. We formulate Ohm's law in the minimal velocity fluid frame and construct a family of resistive solutions that smoothly bridges the gap between the vacuum and the force-free Magnetosphere solutions. The spin-down luminosity, open field line potential drop, and the fraction of open field lines all transition between the vacuum and force-free values as the plasma conductivity varies from zero to infinity. For fixed inclination angle, we find that the spin-down luminosity depends linearly on the open field line potential drop. We consider the implications of our resistive solutions for the spin-down of intermittent pulsars and sub-pulse drift phenomena in radio pulsars.
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time dependent force free pulsar Magnetospheres axisymmetric and oblique rotators
The Astrophysical Journal, 2006Co-Authors: Anatoly SpitkovskyAbstract:Magnetospheres of many astrophysical objects can be accurately described by the low-inertia (or ''force-free'') limit of MHD. We present a new numerical method for solution of equations of force-free relativistic MHD based on the finite-difference time-domain (FDTD) approach with a prescription for handling spontaneous formation of current sheets. We use this method to study the time-dependent evolution of pulsar Magnetospheres in both aligned and oblique magnetic geometries. For the aligned rotator we confirm the general properties of the time-independent solution of Contopoulos et al. (1999). For the oblique rotator we present the 3D structure of the Magnetosphere and compute, for the first time, the spindown power of pulsars as a function of inclination of the magnetic axis. We find the pulsar spindown luminosity to be L {approx} ({mu}{sup 2}{Omega}{sub *}{sup 4}/c{sup 3})(1 + sin{sup 2}{alpha}) for a star with the dipole moment {mu}, rotation frequency {Omega}{sub *}, and magnetic inclination angle {alpha}. We also discuss the effects of current sheet resistivity and reconnection on the structure and evolution of the Magnetosphere.
Philippov Alexander - One of the best experts on this subject based on the ideXlab platform.
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Synthetic gamma-ray lightcurves of Kerr black-hole magnetospheric activity from particle-in-cell simulations
HAL CCSD, 2021Co-Authors: Crinquand Benjamin, Cerutti Benoît, Dubus Guillaume, Parfrey Kyle, Philippov AlexanderAbstract:Context: The origin of ultra-rapid flares of very high-energy radiation from active galactic nuclei remains elusive. Magnetospheric processes, occurring in the close vicinity of the central black hole, could account for these flares. Aims: We aim to bridge the gap between simulations and observations by synthesizing gamma-ray lightcurves in order to characterize the activity of a black-hole Magnetosphere, using kinetic simulations. Methods: We perform global axisymmetric two-dimensional general-relativistic particle-in-cell simulations of a Kerr black-hole Magnetosphere. We include a self-consistent treatment of radiative processes and plasma supply, as well as a realistic magnetic configuration, with a large-scale equatorial current sheet. We couple our particle-in-cell code with a ray-tracing algorithm, in order to produce synthetic lightcurves. Results: These simulations show a highly dynamic Magnetosphere, as well as very efficient dissipation of the magnetic energy. An external supply of magnetic flux is found to maintain the Magnetosphere in a dynamic state, otherwise the Magnetosphere settles in a quasi-steady Wald-like configuration. The dissipated energy is mostly converted to gamma-ray photons. The lightcurves at low viewing angle (face-on) mainly trace the spark gap activity and exhibit high variability. On the other hand, no significant variability is found at high viewing angle (edge-on), where the main contribution comes from the reconnecting current sheet. Conclusions: We observe that black-hole Magnetospheres with a current sheet are characterized by a very high radiative efficiency. The typical amplitude of the flares in our simulations is lower than what is detected in active galactic nuclei. Such flares could result from the variation of parameters external to the black hol
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Synthetic gamma-ray light curves of Kerr black hole magnetospheric activity from particle-in-cell simulations
'EDP Sciences', 2021Co-Authors: Crinquand Benjamin, Cerutti Benoît, Dubus Guillaume, Parfrey Kyle, Philippov AlexanderAbstract:International audienceContext. The origin of ultra-rapid flares of very high-energy radiation from active galactic nuclei remains elusive. Magnetospheric processes, occurring in the close vicinity of the central black hole, could account for these flares.Aims. Our aim is to bridge the gap between simulations and observations by synthesizing gamma-ray light curves in order to characterize the activity of a black hole Magnetosphere, using kinetic simulations.Methods. We performed global axisymmetric 2D general-relativistic particle-in-cell simulations of a Kerr black hole Magnetosphere. We included a self-consistent treatment of radiative processes and plasma supply, as well as a realistic magnetic configuration, with a large-scale equatorial current sheet. We coupled our particle-in-cell code with a ray-tracing algorithm in order to produce synthetic light curves.Results. These simulations show a highly dynamic Magnetosphere, as well as very efficient dissipation of the magnetic energy. An external supply of magnetic flux is found to maintain the Magnetosphere in a dynamic state, otherwise the Magnetosphere settles in a quasi-steady Wald-like configuration. The dissipated energy is mostly converted to gamma-ray photons. The light curves at low viewing angle (face-on) mainly trace the spark gap activity and exhibit high variability. On the other hand, no significant variability is found at high viewing angle (edge-on), where the main contribution comes from the reconnecting current sheet.Conclusions. We observe that black hole Magnetospheres with a current sheet are characterized by a very high radiative efficiency. The typical amplitude of the flares in our simulations is lower than is detected in active galactic nuclei. These flares could result from the variation in parameters external to the black hole.Key words: black hole physics / magnetic fields / acceleration of particles / plasmas / radiation mechanisms: non-thermal / methods: numerical⋆ Movies are available at https://www.aanda.or
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Magnetic Hair and Reconnection in Black Hole Magnetospheres
2021Co-Authors: Bransgrove Ashley, Ripperda Bart, Philippov AlexanderAbstract:The no-hair theorem of general relativity states that isolated black holes are characterized by three parameters: mass, spin, and charge. In this Letter we consider Kerr black holes endowed with highly magnetized plasma-filled Magnetospheres. Using general relativistic kinetic plasma and resistive magnetohydrodynamics simulations, we show that a dipole magnetic field on the event horizon opens into a split-monopole and reconnects in a plasmoid-unstable current-sheet. The no-hair theorem is satisfied, in the sense that all components of the stress-energy tensor decay exponentially in time. We measure the decay time of magnetic flux on the event horizon for plasmoid-dominated reconnection in collisionless and collisional plasma. The reconnecting Magnetosphere should be a powerful source of hard X-ray emission when the magnetic field is strong.Comment: 5 pages, 4 figures, accepted PR
Dt Young - One of the best experts on this subject based on the ideXlab platform.
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Solar wind dynamic pressure and electric field as the main factors controlling Saturn's aurorae
NATURE, 2005Co-Authors: Dt YoungAbstract:The interaction of the solar wind with Earth's Magnetosphere gives rise to the bright polar aurorae and to geomagnetic storms(1), but the relation between the solar wind and the dynamics of the outer planets' Magnetospheres is poorly understood. Jupiter's magnetospheric dynamics and aurorae are dominated by processes internal to the jovian system(2), whereas Saturn's Magnetosphere has generally been considered to have both internal and solar-wind-driven processes. This hypothesis, however, is tentative because of limited simultaneous solar wind and magnetospheric measurements. Here we report solar wind measurements, immediately upstream of Saturn, over a one-month period. When combined with simultaneous ultraviolet imaging(3) we find that, unlike Jupiter, Saturn's aurorae respond strongly to solar wind conditions. But in contrast to Earth, the main controlling factor appears to be solar wind dynamic pressure and electric field, with the orientation of the interplanetary magnetic field playing a much more limited role. Saturn's Magnetosphere is, therefore, strongly driven by the solar wind, but the solar wind conditions that drive it differ from those that drive the Earth's Magnetosphere.
Markku Alho - One of the best experts on this subject based on the ideXlab platform.
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simulation of mercury s magnetosheath with a combined hybrid paraboloid model
Journal of Geophysical Research, 2017Co-Authors: David Parunakian, S Dyadechkin, I I Alexeev, E S Belenkaya, M L Khodachenko, Esa Kallio, Markku AlhoAbstract:In this paper we introduce a novel approach for modelling planetary Magnetospheres that involves a combination of the hybrid model and the Paraboloid Magnetosphere Model (PMM); we further refer to it as the Combined Hybrid Model (CHM). While both of these individual models have been successfully applied in the past, their combination enables us to both overcome the traditional difficulties of hybrid models to develop a self-consistent magnetic field and to compensate the lack of plasma simulation in the PMM. We then use this combined model to simulate Mercury's Magnetosphere and investigate the geometry and configuration of Mercury's magnetosheath controlled by various conditions in the interplanetary medium. The developed approach provides a unique comprehensive view of Mercury's magnetospheric environment for the first time. Using this setup we compare the locations of the bow shock and the magnetopause as determined by simulations with the locations predicted by standalone PMM runs, and also verify the magnetic and dynamic pressure balance at the magnetopause. We also compare the results produced by these simulations with observational data obtained by the magnetometer on board the MESSENGER spacecraft along a dusk-dawn orbit, and discuss the signatures of the magnetospheric features that appear in these simulations. Overall, our analysis suggests that combining the semi-empirical PMM with a self-consistent global kinetic model creates new modelling possibilities which individual models cannot provide on their own.