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1
Pensionerov, Ivan A., Elena S. Belenkaya, Stanley W. H. Cowley, Igor I. Alexeev, Vladimir V. Kalegaev, and David A. Parunakian. "Magnetodisc modelling in Jupiter's magnetosphere using Juno magnetic field data and the paraboloid magnetic field model." Annales Geophysicae 37, no. 1 (February 5, 2019): 101–9. http://dx.doi.org/10.5194/angeo-37-101-2019.
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Abstract. One of the main features of Jupiter's magnetosphere is its equatorial magnetodisc, which significantly increases the field strength and size of the magnetosphere. Analysis of Juno measurements of the magnetic field during the first 10 orbits covering the dawn to pre-dawn sector of the magnetosphere (∼03:30–06:00 local time) has allowed us to determine optimal parameters of the magnetodisc using the paraboloid magnetospheric magnetic field model, which employs analytic expressions for the magnetospheric current systems. Specifically, within the model we determine the size of the Jovian magnetodisc and the magnetic field strength at its outer edge.
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Paty, Carol, Chris S. Arridge, Ian J. Cohen, Gina A. DiBraccio, Robert W. Ebert, and Abigail M. Rymer. "Ice giant magnetospheres." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2187 (November 9, 2020): 20190480. http://dx.doi.org/10.1098/rsta.2019.0480.
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The ice giant planets provide some of the most interesting natural laboratories for studying the influence of large obliquities, rapid rotation, highly asymmetric magnetic fields and wide-ranging Alfvénic and sonic Mach numbers on magnetospheric processes. The geometries of the solar wind–magnetosphere interaction at the ice giants vary dramatically on diurnal timescales due to the large tilt of the magnetic axis relative to each planet's rotational axis and the apparent off-centred nature of the magnetic field. There is also a seasonal effect on this interaction geometry due to the large obliquity of each planet (especially Uranus). With in situ observations at Uranus and Neptune limited to a single encounter by the Voyager 2 spacecraft, a growing number of analytical and numerical models have been put forward to characterize these unique magnetospheres and test hypotheses related to the magnetic structures and the distribution of plasma observed. Yet many questions regarding magnetospheric structure and dynamics, magnetospheric coupling to the ionosphere and atmosphere, and potential interactions with orbiting satellites remain unanswered. Continuing to study and explore ice giant magnetospheres is important for comparative planetology as they represent critical benchmarks on a broad spectrum of planetary magnetospheric interactions, and provide insight beyond the scope of our own Solar System with implications for exoplanet magnetospheres and magnetic reversals. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems'.
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Alexeev, I. I., and E. S. Belenkaya. "Modeling of the Jovian Magnetosphere." Annales Geophysicae 23, no. 3 (March 30, 2005): 809–26. http://dx.doi.org/10.5194/angeo-23-809-2005.
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Abstract. This paper presents a global model of the Jovian magnetosphere which is valid not only in the equatorial plane and near the planet, as most of the existing models are, but also at high latitudes and in the outer regions of the magnetosphere. The model includes the Jovian dipole, magnetodisc, and tail current system. The tail currents are combined with the magnetopause closure currents. All inner magnetospheric magnetic field sources are screened by the magnetopause currents. It guarantees a zero normal magnetic field component for the inner magnetospheric field at the whole magnetopause surface. By changing magnetospheric scale (subsolar distance), the model gives a possibility to study the solar wind influence on the magnetospheric structure and auroral activity. A dependence of the magnetospheric size on the solar wind dynamic pressure psw (proportional to psw-0.23) is obtained. It is a stronger dependence than in the case of the Earth's magnetosphere (psw-1/6). The model of Jupiter's magnetospheric which is presented is a unique one, as it allows one to study the solar wind and interplanetary magnetic field (IMF) effects.
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Kalegaev, Vladimir V., Natalia A. Vlasova, Ilya S. Nazarkov, and Sophia A. Melkova. "Magnetospheric access for solar protons during the January 2005 SEP event." Journal of Space Weather and Space Climate 8 (2018): A55. http://dx.doi.org/10.1051/swsc/2018040.
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The early phase of the extraordinary solar energetic particle 20 January, 2005 event having the highest peak flux of any SEP in the past 50 years of protons with energies > 100 MeV is studied. Solar energetic particles (>16 MeV) entry to the Earth’s magnetosphere on January 20, 2005 under northward interplanetary magnetic field conditions is considered based on multi-satellite data analysis and magnetic field simulation. Solar wind parameters and interplanetary magnetic field data, as well as calculations in terms of the A2000 magnetospheric magnetic field model were used to specify conditions in the Earth’s environment corresponding to solar proton event. It was shown that during the early phase of the event energetic particle penetration into the magnetosphere took place in the regions on the magnetopause where the magnetospheric and interplanetary magnetic field vectors are parallel. Complex analysis of the experimental data on particle fluxes in the interplanetary medium (data from ACE spacecraft) and on low-altitude (POES) and geosynchronous (GOES) orbits inside the Earth’s magnetosphere show two regions on the magnetopause responsible for particle access to the magnetosphere: the near equatorial day-side region and open field lines window at the high-latitude magnetospheric boundary. Calculations in terms of A2000 magnetospheric magnetic field model and comparison with SuperDARN images support the link between high-latitude solar energetic particle precipitations and the region at the magnetopause where the magnetospheric field is coupled with northward IMF, allowing solar particles entrance into the magnetosphere and access to the northern polar cap.
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Krtička, J., Z. Mikulášek, P. Kurfürst, and M. E. Oksala. "Photometric signatures of corotating magnetospheres of hot stars governed by higher-order magnetic multipoles." Astronomy & Astrophysics 659 (March 2022): A37. http://dx.doi.org/10.1051/0004-6361/202141997.
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Context. The light curves of magnetic, chemically peculiar stars typically show periodic variability due to surface spots that in most cases can be modeled by low-order harmonic expansion. However, high-precision satellite photometry reveals tiny complex features in the light curves of some of these stars that are difficult to explain as caused by a surface phenomenon under reasonable assumptions. These features might originate from light extinction in corotating magnetospheric clouds supported by a complex magnetic field dominated by higher-order multipoles. Aims. We aim to understand the photometric signatures of corotating magnetospheres that are governed by higher-order multipoles. Methods. We determined the location of magnetospheric clouds from the minima of the effective potential along the magnetic field lines for different orders of multipoles and their combination. From the derived magnetospheric density distribution, we calculated light curves accounting for absorption and subsequent emission of light. Results. For axisymmetric multipoles, the rigidly rotating magnetosphere model is able to explain the observed tiny features in the light curves only when the higher-order multipoles dominate the magnetic field not only at the stellar surface, but even at the Kepler radius. However, even a relatively weak nonaxisymmetric component leads to warping of equilibrium surfaces. This introduces structures that can explain the tiny features observed in the light curves of chemically peculiar stars. The light emission contributes to the light variability only if a significant fraction of light is absorbed in the magnetosphere.
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Jasinski, Jamie M., Neil Murphy, Xianzhe Jia, and James A. Slavin. "Neptune’s Pole-on Magnetosphere: Dayside Reconnection Observations by Voyager 2." Planetary Science Journal 3, no. 4 (April 1, 2022): 76. http://dx.doi.org/10.3847/psj/ac5967.
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Abstract The “pole-on” configuration occurs when the polar magnetosphere of a planet is directed into the solar wind velocity vector. Such magnetospheric configurations are unique to the ice giant planets. This means that magnetic reconnection, a process that couples a magnetosphere to the solar wind, will be different at the ice giants when they are pole-on compared to other planets. The only available in situ measurements of a pole-on magnetosphere are from the Neptune flyby by Voyager 2, which we analyze in this paper. We show that dayside magnetopause conditions were conducive to magnetic reconnection. A plasma depletion layer in the magnetosheath adjacent to the magnetopause was observed. Plasma measurements inside the magnetospheric cusp show evidence of multiple reconnection taking place at the magnetopause before the spacecraft crossed the open–closed field line boundary. A possible traveling compression region from a nearby passing flux rope was also observed, providing further supporting evidence that multiple X-line reconnection occurred during the flyby. During a perfectly pole-on configuration, reconnection will not depend on the orientation of the interplanetary magnetic field, as is the case at other planetary magnetospheres. The rate of reconnection will not vary because the area of the dayside magnetopause where antiparallel shears occur will be approximately equal for all interplanetary magnetic field orientations. Therefore, we suggest that rotating into and out of the pole-on configuration will likely drive the “on–off”/“switch-like” dynamics observed in simulations. Consequently, the pole-on configuration is most likely an important rotational phase for driving ice giant magnetospheric dynamics.
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Peymirat, C., and D. Fontaine. "A numerical method to compute Euler potentials for non dipolar magnetic fields." Annales Geophysicae 17, no. 3 (March 31, 1999): 328–37. http://dx.doi.org/10.1007/s00585-999-0328-6.
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Abstract. The magnetospheric magnetic field may be conveniently described by two scalar functions (α, β), known as the Euler potentials. They are not uniquely defined, and they may be difficult to derive for configuration more complex than a simple dipole. We propose here a simple numerical method to compute one possible pair (α, β). In magnetospheric regions of closed field lines, α can be chosen as a function of the tube volume of unit magnetic flux. The method can be applied to a wide class of magnetic fields which describe the magnetospheric domain of closed field lines and the conjugated ionosphere. Here, it is used with the T87 Tsyganenko model. The results coincide with the dipolar potentials at close distances from the Earth. At larger distances, they display an increasing distortion with the radial distance (or the invariant latitude in the ionosphere) and the magnetic activity. In the magnetosphere, the contours of α and β are stretched towards the nightside. In the ionosphere, they also extend towards the nightside and present major distortions in a narrow ring at the polar cap boundary, which maps distant boundary layers in the magnetosphere.Key words. Ionosphere (ionosphere-magnetosphere interactions; modeling and forecasting). Magnetospheric physics (plasma convection).
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Zaharia, S., C. Z. Cheng, and K. Maezawa. "3-D force-balanced magnetospheric configurations." Annales Geophysicae 22, no. 1 (January 1, 2004): 251–65. http://dx.doi.org/10.5194/angeo-22-251-2004.
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Abstract. The knowledge of plasma pressure is essential for many physics applications in the magnetosphere, such as computing magnetospheric currents and deriving mag-netosphere-ionosphere coupling. A thorough knowledge of the 3-D pressure distribution has, however, eluded the community, as most in situ pressure observations are either in the ionosphere or the equatorial region of the magnetosphere. With the assumption of pressure isotropy there have been attempts to obtain the pressure at different locations,by either (a) mapping observed data (e.g. in the ionosphere) along the field lines of an empirical magnetospheric field model, or (b) computing a pressure profile in the equatorial plane (in 2-D) or along the Sun-Earth axis (in 1-D) that is in force balance with the magnetic stresses of an empirical model. However, the pressure distributions obtained through these methods are not in force balance with the empirical magnetic field at all locations. In order to find a global 3-D plasma pressure distribution in force balance with the magnetospheric magnetic field, we have developed the MAG-3-D code that solves the 3-D force balance equation computationally. Our calculation is performed in a flux coordinate system in which the magnetic field is expressed in terms of Euler potentials as . The pressure distribution, , is prescribed in the equatorial plane and is based on satellite measurements. In addition, computational boundary conditions for ψ surfaces are imposed using empirical field models. Our results provide 3-D distributions of magnetic field, plasma pressure, as well as parallel and transverse currents for both quiet-time and disturbed magnetospheric conditions. Key words. Magnetospheric physics (magnetospheric configuration and dynamics; magnetotail; plasma sheet)
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Vaisberg, O. L., L. A. Avanov, T. E. Moore, and V. N. Smirnov. "Ion velocity distributions within the LLBL and their possible implication to multiple reconnections." Annales Geophysicae 22, no. 1 (January 1, 2004): 213–36. http://dx.doi.org/10.5194/angeo-22-213-2004.
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Abstract. We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-type, and (c) distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Χ-lines between magnetosheath and magnetospheric flux tubes. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions)
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Belenkaya, E. S., P. A. Bespalov, S. S. Davydenko, and V. V. Kalegaev. "Magnetic field influence on aurorae and the Jovian plasma disk radial structure." Annales Geophysicae 24, no. 3 (May 19, 2006): 973–88. http://dx.doi.org/10.5194/angeo-24-973-2006.
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Abstract. The Jovian paraboloid magnetospheric model is applied for the investigation of the planet's auroral emission and plasma disk structure in the middle magnetosphere. Jupiter's auroral emission demonstrates the electrodynamic coupling between the ionosphere and magnetosphere. For comparison of different regions in the ionospheric level and in the magnetosphere, the paraboloid model of the global magnetospheric magnetic field is used. This model provides mapping along highly-conducting magnetic field lines. The paraboloid magnetic field model is also applied for consideration of the stability of the background plasma disk in the rotating Jupiter magnetosphere with respect to the flute perturbations. Model radial distribution of the magnetic field and experimental data on the plasma angular velocity in the middle Jovian magnetosphere are used. A dispersion relation of the plasma perturbations in the case of a perfectly conducting ionosphere is obtained. Analyzing starting conditions of a flute instability in the disk, the "threshold" radial profile of the plasma density is determined. An application of the results obtained to the known data on the Jovian plasma disk is discussed.
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Alberti, Tommaso, Mirko Piersanti, Antonio Vecchio, Paola De Michelis, Fabio Lepreti, Vincenzo Carbone, and Leonardo Primavera. "Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations." Annales Geophysicae 34, no. 11 (November 22, 2016): 1069–84. http://dx.doi.org/10.5194/angeo-34-1069-2016.
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Abstract. We used the empirical mode decomposition (EMD) to investigate the time variation of the magnetospheric and ground-based observations of the Earth's magnetic field during both quiet and disturbed periods. We found two timescale variations in magnetospheric data which are associated with different magnetospheric current systems and the characteristic diurnal orbital variation, respectively. On the ground we identified three timescale variations related to the solar-wind–magnetosphere high-frequency interactions, the ionospheric processes, and the internal dynamics of the magnetosphere. This approach is able to identify the different physical processes involved in solar-wind–magnetosphere–ionosphere coupling. In addition, the large-timescale contribution can be used as a local index for the identification of the intensity of a geomagnetic storm on the ground.
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Alexeev, I. I., E. S. Belenkaya, S. Yu Bobrovnikov, V. V. Kalegaev, J. A. Cumnock, and L. G. Blomberg. "Magnetopause mapping to the ionosphere for northward IMF." Annales Geophysicae 25, no. 12 (January 2, 2007): 2615–25. http://dx.doi.org/10.5194/angeo-25-2615-2007.
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Abstract. We study the topological structure of the magnetosphere for northward IMF. Using a magnetospheric magnetic field model we study the high-latitude response to prolonged periods of northward IMF. For forced solar wind conditions we investigate the location of the polar cap region, the polar cap potential drop, and the field-aligned acceleration potentials, depending on the solar wind pressure and IMF By and Bx changes. The open field line bundles, which connect the Earth's polar ionosphere with interplanetary space, are calculated. The locations of the magnetospheric plasma domains relative to the polar ionosphere are studied. The specific features of the open field line regions arising when IMF is northward are demonstrated. The coefficients of attenuation of the solar wind magnetic and electric fields which penetrate into the magnetosphere are determined.
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Willis, D. M., A. C. Holder, and C. J. Davis. "Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals." Annales Geophysicae 18, no. 1 (January 31, 2000): 11–27. http://dx.doi.org/10.1007/s00585-000-0011-4.
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Abstract. Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals are investigated by considering the idealized problem of a magnetic multipole of order m and degree n located at the centre of a spherical cavity surrounded by a boundless perfect diamagnetic medium. In this illustrative idealization, the fixed spherical (magnetopause) boundary layer behaves as a perfectly conducting surface that shields the external diamagnetic medium from the compressed multipole magnetic field, which is therefore confined within the spherical cavity. For a general magnetic multipole of degree n, the non-radial components of magnetic induction just inside the magnetopause are increased by the factor {1 + [(n + 1)/n]} relative to their corresponding values in the absence of the perfectly conducting spherical magnetopause. An exact equation is derived for the magnetic field lines of an individual zonal (m = 0), or axisymmetric, magnetic multipole of arbitrary degree n located at the centre of the magnetospheric cavity. For such a zonal magnetic multipole, there are always two neutral points and n-1 neutral rings on the spherical magnetopause surface. The two neutral points are located at the poles of the spherical magnetopause. If n is even, one of the neutral rings is coincident with the equator; otherwise, the neutral rings are located symmetrically with respect to the equator. The actual existence of idealized higher-degree (n>1) axisymmetric magnetospheres would necessarily imply multiple (n + 1) magnetospheric cusps and multiple (n) ring currents. Exact equations are also derived for the magnetic field lines of an individual non-axisymmetric magnetic multipole, confined by a perfectly conducting spherical magnetopause, in two special cases; namely, a symmetric sectorial multipole (m = n) and an antisymmetric sectorial multipole (m = n-1). For both these non-axisymmetric magnetic multipoles, there exists on the spherical magnetopause surface a set of neutral points linked by a network of magnetic field lines. Novel magnetospheric processes are likely to arise from the existence of magnetic neutral lines that extend from the magnetopause to the surface of the Earth. Finally, magnetic field lines that are confined to, or perpendicular to, either special meridional planes or the equatorial plane, when the multipole is in free space, continue to be confined to, or perpendicular to, these same planes when the perfectly conducting magnetopause is present.Key words. Geomagnetism and paleomagnetism (reversals-process, time scale, magnetostratigraphy) · Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetospheric configuration and dynamics)
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Feldstein, Y. I., L. I. Gromova, A. Grafe, C. I. Meng, V. V. Kalegaev, I. I. Alexeev, and Y. P. Sumaruk. "Auroral electrojet dynamics during magnetic storms, connection with plasma precipitation and large-scale structure of the magnetospheric magnetic field." Annales Geophysicae 17, no. 4 (April 30, 1999): 497–507. http://dx.doi.org/10.1007/s00585-999-0497-3.
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Abstract. Effect of the equatorward shift of the eastward and westward electrojets during magnetic storms main phase is analyzed based on the meridional chains of magnetic observatories EISCAT and IMAGE and several Russian observatories (geomagnetic longitude ~110°, corrected geomagnetic latitudes 74°F 51°.) Magnetic storms of various Dst index intensity where the main phase falls on 1000 UT - 2400 UT interval were selected so that one of the observatory chains was located in the afternoon - near midnight sector of MLT. The eastward electrojet center shifts equatorward with Dst intensity increase: when Dst ~ - 50 nT the electrojet center is located at F ~ 62°, when Dst ~ -300 nT it is placed at F ~54°. The westward electrojet center during magnetic storms main phase for intervals between substorms shifts equatorward with Dst increase: at F~ 62° when Dst ~ -100 nT and at F ~ 55° when Dst ~ -300 nT. During substorms within the magnetic storms intervals the westward electrojet widens poleward covering latitudes F~ 64°- 65°. DMSP (F08, F10 and F11) satellite observations of auroral energy plasma precipitations at upper atmosphere altitudes were used to determine precipitation region structure and location of boundaries of various plasma domains during magnetic storms on May 10-11, 1992, February 5-7 and February 21-22, 1994. Interrelationships between center location, poleward and equatorward boundaries of electrojets and characteristic plasma regions are discussed. The electrojet center, poleward and equatorward boundaries along the magnetic observatories meridional chain were mapped to the magnetosphere using the geomagnetic field paraboloid model. The location of auroral energy oxygen ion regions in the night and evening magnetosphere is determined. Considerations are presented on the mechanism causing the appearance in the inner magnetosphere during active intervals of magnetic storms of ions with energy of tens KeV. In the framework of the magnetospheric magnetic field paraboloid model the influence of the ring current and magnetospheric tail plasma sheet currents on large-scale magnetosphere structure is considered.Key words. Ionosphere (particle precipitation) · Magnetospheric physics (current systems; magnetospheric configuration and dynamics).
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Matsui, H., J. M. Quinn, R. B. Torbert, V. K. Jordanova, P. A. Puhl-Quinn, and G. Paschmann. "IMF <i>B<sub>Y</sub></i> and the seasonal dependences of the electric field in the inner magnetosphere." Annales Geophysicae 23, no. 7 (October 14, 2005): 2671–78. http://dx.doi.org/10.5194/angeo-23-2671-2005.
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Abstract. It is known that the electric field pattern at high latitudes depends on the polarity of the Y component of the interplanetary magnetic field (IMF BY) and season. In this study, we investigate the seasonal and BY dependences in the inner magnetosphere using the perigee (4<L<10) Cluster data taken from low magnetic latitudes. The data consist of both components of the electric field perpendicular to the magnetic field, obtained by the electron drift instrument (EDI), which is based on a newly developed technique, well suited for measurement of the electric fields in the inner magnetosphere. These data are sorted by the polarities of IMF BZ and BY, and by seasons or hemispheres. It is demonstrated from our statistics that the electric fields in the inner magnetosphere depend on these quantities. The following three points are inferred: 1) The electric fields exhibit some differences statistically between Cluster locations at the Northern and Southern Hemispheres with the same dipole L and magnetic local time (MLT) values and during the same IMF conditions. These differences in the electric fields might result from hemispherical differences in magnetic field geometry and/or those in field-aligned potential difference. 2) The IMF BY and seasonal dependence of the dawnside and duskside electric fields at 4<L<10 is consistent with that seen in the polar convection cell. In addition, it is possible that these dependences are affected by the ionospheric conductivity and the field-aligned current. 3) The nightside electric field in the inner magnetosphere measured by Cluster is often similar to that in the magnetotail lobe. In the future, it will be necessary to incorporate these dependencies on IMF BY and season into a realistic model of the inner magnetospheric convection electric field. Keywords. Magnetospheric physics (Electric fields; Magnetosphere-ionosphere interactions; Solar windmagnetosphere interactions)
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Glassmeier, K. H., J. Vogt, A. Stadelmann, and S. Buchert. "Concerning long-term geomagnetic variations and space climatology." Annales Geophysicae 22, no. 10 (November 3, 2004): 3669–77. http://dx.doi.org/10.5194/angeo-22-3669-2004.
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Abstract. During geomagnetic polarity transitions the surface magnetic field of the Earth decays to about 25% and less of its present value. This implies a shrinking of the terrestrial magnetosphere and posses the question of whether magnetospheric magnetic field variations scale in the same manner. Furthermore, the geomagnetic main field also controls the magnetospheric magnetic field and space weather conditions. Long-term geomagnetic variations are thus intimately related to space climate. We critically assess existing scaling relations and derive new ones for various magnetospheric parameters. For example, we find that ring current perturbations do not increase with decreasing dipole moment. And we derive a scaling relation for the polar electrojet contribution, indicating a weak increase with increasing internal field. From this we infer that the ratio between external and internal field contributions may be weakly enhanced during polarity transitions. Our scaling relations also provide more insight on the importance of the internal geomagnetic field contribution for space climate.
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Taktakishvili, A., A. Greco, G. Zimbardo, P. Veltri, G. Cimino, L. Zelenyi, and R. E. Lopez. "The penetration of ions into the magnetosphere through the magnetopause turbulent current sheet." Annales Geophysicae 21, no. 9 (September 30, 2003): 1965–73. http://dx.doi.org/10.5194/angeo-21-1965-2003.
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Abstract. This paper reports the results of numerical modeling of magnetosheath ion motion in the magnetopause current sheet (MCS) in the presence of magnetic fluctuations. Our model of magnetic field turbulence has a power law spectrum in the wave vector space, reaches maximum intensity in the center of MCS, and decreases towards the magnetosheath and magnetosphere boundaries. We calculated the density profile across the MCS. We also calculated the number of particles entering the magnetosphere, reflected from the magnetopause and escaping from the flanks, as a function of the fluctuation level of the turbulence and magnetic field shear parameter. All of these quantities appeared to be strongly dependent on the fluctuation level, but not on the magnetic field shear parameter. For the highest fluctuation levels the number of particles entering the magnetosphere does not exceed 15% of the total number of particles launched from the magnetosheath side of the MCS; the modeling also reproduced the effective reflection of the magnetosheath flow from very high levels of magnetic fluctuations.Key words. Magnetospheric physics (magnetosheath; magnetospheric configuration and dynamics; turbulence)
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Olsson, A., P. Janhunen, T. Karlsson, N. Ivchenko, and L. G. Blomberg. "Statistics of Joule heating in the auroral zone and polar cap using Astrid-2 satellite Poynting flux." Annales Geophysicae 22, no. 12 (December 22, 2004): 4133–42. http://dx.doi.org/10.5194/angeo-22-4133-2004.
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Abstract. We make a statistical study of ionospheric Joule heating with the Poynting flux method using six months of Astrid-2/EMMA electric and magnetic field data during 1999 (solar maximum year). For the background magnetic field we use the IGRF model. Our results are in agreement with earlier statistical satellite studies using both the ΣPE2 method and the Poynting flux method. We present a rather comprehensive set of fitted Joule heating formulas expressing the Joule heating in given magnetic local time (MLT) and invariant latitude (ILAT) range under given solar illumination conditions as a function of the Kp index, the AE index, the Akasofu epsilon parameter and the solar wind kinetic energy flux. The study thus provides improved and more detailed estimates of the statistical Joule heating. Such estimates are necessary building blocks for future quantitative studies of the power budget in the magnetosphere and in the nightside auroral region. Key words. Ionosphere (electric fields and currents; ionosphere-magnetosphere interactions) – Magnetospheric physics (magnetospheric configuration and dynamics)
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Spitkovsky, Anatoly. "Modeling of pulsar magnetospheres." Proceedings of the International Astronomical Union 8, S291 (August 2012): 291. http://dx.doi.org/10.1017/s1743921312023897.
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AbstractThe inner workings of pulsar magnetospheres have fascinated and confused researchers since the discovery of pulsars. I will review the status of magnetospheric models, including vacuum, space-charge-limited and resistive force-free MHD. I will highlight model predictions for the integrated pulsar quantities (such as spin down and torques) and the observational consequences of calculated magnetic field structure. Particularly, high-energy emission from pulsars allows putting new constraints on the geometry of the emission region and the physics of particle acceleration in the magnetosphere.
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Tang, S. Y., Y. C. Zhang, L. Dai, T. Chen, and C. Wang. "MMS Observation of the Hall Field in an Asymmetric Magnetic Reconnection with Guide Field." Astrophysical Journal 922, no. 2 (November 24, 2021): 96. http://dx.doi.org/10.3847/1538-4357/ac31b1.
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Abstract In this paper, we investigate the structure of out-of-plane magnetic field in the reconnection event observed by Magnetospheric Multiscale Mission at the magnetopause of the Earth magnetosphere on 2015 October 21. We find that the perturbation of out-of-plane magnetic field in this event is different from previous observations of the quadrupolar Hall magnetic field. The distinct out-of-plane magnetic field is interpreted as a part of the hexapolar Hall magnetic field obtained in a recent simulation of asymmetric reconnection with the guide field. This is significant evidence of the hexapolar Hall magnetic field in collisionless magnetic reconnection from the observations in the magnetosphere. High-resolution measurements of particle and field are used to provide a comprehensive description of the features of the hexapolar Hall magnetic field. The results from this study offer an insight into the Hall effect in collisionless magnetic reconnection.
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Belenkaya, E. S., S. W. H. Cowley, V. V. Kalegaev, O. G. Barinov, and W. O. Barinova. "Magnetic interconnection of Saturn's polar regions: comparison of modelling results with Hubble Space Telescope UV auroral images." Annales Geophysicae 31, no. 8 (August 28, 2013): 1447–58. http://dx.doi.org/10.5194/angeo-31-1447-2013.
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Abstract. We consider the magnetic interconnection of Saturn's northern and southern polar regions controlled by the interplanetary magnetic field (IMF), studying in particular the more complex and interesting case of southward IMF, when the Kronian magnetospheric magnetic field structure is the most twisted. The simpler case of northward IMF is also discussed. Knowledge of the magnetospheric magnetic field structure is very significant, for example, for investigation of the electric fields and field-aligned currents in Saturn's environment, particularly those which cause the auroral emissions. Here we modify the paraboloid magnetospheric magnetic field model employed in previous related studies by including higher multipole terms in Saturn's internal magnetic field, required for more detailed considerations of inter-hemispheric conjugacy, together with inclusion of a spheroidal boundary at the ionospheric level. The model is employed to map Southern Hemisphere auroral regions observed by the Hubble Space Telescope (HST) in 2008 under known IMF conditions to both the equatorial plane and the northern ionosphere. It is shown that the brightest auroral features map typically to the equatorial region between the central ring current and the outer magnetosphere, and that auroral features should be largely symmetric between the two hemispheres, except for a small poleward displacement and latitudinal narrowing in the Northern Hemisphere compared with the Southern Hemisphere due to the quadrupole field asymmetry. The latter features are in agreement with the conjugate auroras observed under near-equinoctial conditions in early 2009, when IMF data are not available.
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TSYGANENKO, N. A. "Models of Magnetospheric Magnetic Field." Journal of geomagnetism and geoelectricity 43, Supplement1 (1991): 325–36. http://dx.doi.org/10.5636/jgg.43.supplement1_325.
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Vidotto, A. A., M. Jardine, J. Morin, J. F. Donati, P. Lang, and A. J. B. Russell. "Planetary protection in the extreme environments of low-mass stars." Proceedings of the International Astronomical Union 9, S302 (August 2013): 237–38. http://dx.doi.org/10.1017/s1743921314002166.
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AbstractRecent results showed that the magnetic field of M-dwarf (dM) stars, currently the main targets in searches for terrestrial planets, is very different from the solar one, both in topology as well as in intensity. In particular, the magnetised environment surrounding a planet orbiting in the habitable zone (HZ) of dM stars can differ substantially to the one encountered around the Earth. These extreme magnetic fields can compress planetary magnetospheres to such an extent that a significant fraction of the planet's atmosphere may be exposed to erosion by the stellar wind. Using observed surface magnetic maps for a sample of 15 dM stars, we investigate the minimum degree of planetary magnetospheric compression caused by the intense stellar magnetic fields. We show that hypothetical Earth-like planets with similar terrestrial magnetisation (~1 G) orbiting at the inner (outer) edge of the HZ of these stars would present magnetospheres that extend at most up to 6.1 (11.7) planetary radii. To be able to sustain an Earth-sized magnetosphere, the terrestrial planet would either need to orbit significantly farther out than the traditional limits of the HZ; or else, if it were orbiting within the life-bearing region, it would require a minimum magnetic field ranging from a few G to up to a few thousand G.
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Zhang, Binzheng, Peter A. Delamere, Zhonghua Yao, Bertrand Bonfond, D. Lin, Kareem A. Sorathia, Oliver J. Brambles, et al. "How Jupiter’s unusual magnetospheric topology structures its aurora." Science Advances 7, no. 15 (April 2021): eabd1204. http://dx.doi.org/10.1126/sciadv.abd1204.
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Jupiter’s bright persistent polar aurora and Earth’s dark polar region indicate that the planets’ magnetospheric topologies are very different. High-resolution global simulations show that the reconnection rate at the interface between the interplanetary and jovian magnetic fields is too slow to generate a magnetically open, Earth-like polar cap on the time scale of planetary rotation, resulting in only a small crescent-shaped region of magnetic flux interconnected with the interplanetary magnetic field. Most of the jovian polar cap is threaded by helical magnetic flux that closes within the planetary interior, extends into the outer magnetosphere, and piles up near its dawnside flank where fast differential plasma rotation pulls the field lines sunward. This unusual magnetic topology provides new insights into Jupiter’s distinctive auroral morphology.
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Němec, František, and Marie Kotková. "Evaluating the Accuracy of Magnetospheric Magnetic Field Models Using Cluster Spacecraft Magnetic Field Measurements." Universe 7, no. 8 (August 3, 2021): 282. http://dx.doi.org/10.3390/universe7080282.
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Magnetic fields in the inner magnetosphere can be obtained as vector sums of the Earth’s own internal magnetic field and magnetic fields stemming from currents flowing in the space plasma. While the Earth’s internal magnetic field is accurately described by the International Geomagnetic Reference Field (IGRF) model, the characterization of the external magnetic fields is significantly more complicated, as they are highly variable and dependent on the actual level of the geomagnetic activity. Tsyganenko family magnetic field models (T89, T96, T01, TA15B, TA15N), parameterized by the geomagnetic activity level and solar wind parameters, are often used by the involved community to describe these fields. In the present paper, we use a large dataset (2001–2018) of magnetospheric magnetic field measurements obtained by the four Cluster spacecraft to assess the accuracy of these models. We show that, while the newer models (T01, TA15B, TA15N) perform significantly better than the old ones (T89, T96), there remain some systematic deviations, in particular at larger latitudes. Moreover, we compare the locations of the min-B equator determined using the four-point Cluster spacecraft measurements with the locations determined using the magnetic field models. We demonstrate that, despite the newer models being comparatively slightly more accurate, an uncertainty of about one degree in the latitude of the min-B equator remains.
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Lai, Ching-Ming, and Jean-Fu Kiang. "Comparative Study on Planetary Magnetosphere in the Solar System." Sensors 20, no. 6 (March 17, 2020): 1673. http://dx.doi.org/10.3390/s20061673.
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The magnetospheric responses to solar wind of Mercury, Earth, Jupiter and Uranus are compared via magnetohydrodynamic (MHD) simulations. The tilt angle of each planetary field and the polarity of solar wind are also considered. Magnetic reconnection is illustrated and explicated with the interaction between the magnetic field distributions of the solar wind and the magnetosphere.
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Le, G., C. T. Russell, and K. Takahashi. "Morphology of the ring current derived from magnetic field observations." Annales Geophysicae 22, no. 4 (April 2, 2004): 1267–95. http://dx.doi.org/10.5194/angeo-22-1267-2004.
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Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ~3 RE and a main westward ring current at ~4–7 RE for all levels of geomagnetic disturbances. In general, the in-situ observations show that the ring current varies as the Dst index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (~0.5MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ~3MA, whereas the total symmetric ring current is ~1MA. Thus, the partial ring current contributes dominantly to the decrease in the Dst index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn. Key words. Magnetospheric physics (current systems; storms and substorms; magnetospheric configuration and dynamics)
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Belenkaya, Elena S., Stanley W. H. Cowley, Igor I. Alexeev, Vladimir V. Kalegaev, Ivan A. Pensionerov, Marina S. Blokhina, and David A. Parunakian. "Open and partially closed models of the solar wind interaction with outer planet magnetospheres: the case of Saturn." Annales Geophysicae 35, no. 6 (December 6, 2017): 1293–308. http://dx.doi.org/10.5194/angeo-35-1293-2017.
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Abstract. A wide variety of interactions take place between the magnetized solar wind plasma outflow from the Sun and celestial bodies within the solar system. Magnetized planets form magnetospheres in the solar wind, with the planetary field creating an obstacle in the flow. The reconnection efficiency of the solar-wind-magnetized planet interaction depends on the conditions in the magnetized plasma flow passing the planet. When the reconnection efficiency is very low, the interplanetary magnetic field (IMF) does not penetrate the magnetosphere, a condition that has been widely discussed in the recent literature for the case of Saturn. In the present paper, we study this issue for Saturn using Cassini magnetometer data, images of Saturn's ultraviolet aurora obtained by the HST, and the paraboloid model of Saturn's magnetospheric magnetic field. Two models are considered: first, an open model in which the IMF penetrates the magnetosphere, and second, a partially closed model in which field lines from the ionosphere go to the distant tail and interact with the solar wind at its end. We conclude that the open model is preferable, which is more obvious for southward IMF. For northward IMF, the model calculations do not allow us to reach definite conclusions. However, analysis of the observations available in the literature provides evidence in favor of the open model in this case too. The difference in magnetospheric structure for these two IMF orientations is due to the fact that the reconnection topology and location depend on the relative orientation of the IMF vector and the planetary dipole magnetic moment. When these vectors are parallel, two-dimensional reconnection occurs at the low-latitude neutral line. When they are antiparallel, three-dimensional reconnection takes place in the cusp regions. Different magnetospheric topologies determine different mapping of the open-closed boundary in the ionosphere, which can be considered as a proxy for the poleward edge of the auroral oval.
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Wild, J. A., S. W. H. Cowley, J. A. Davies, H. Khan, M. Lester, S. E. Milan, G. Provan, et al. "First simultaneous observations of flux transfer events at the high-latitude magnetopause by the Cluster spacecraft and pulsed radar signatures in the conjugate ionosphere by the CUTLASS and EISCAT radars." Annales Geophysicae 19, no. 10/12 (September 30, 2001): 1491–508. http://dx.doi.org/10.5194/angeo-19-1491-2001.
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Abstract. Cluster magnetic field data are studied during an outbound pass through the post-noon high-latitude magnetopause region on 14 February 2001. The onset of several minute perturbations in the magnetospheric field was observed in conjunction with a southward turn of the interplanetary magnetic field observed upstream by the ACE spacecraft and lagged to the subsolar magnetopause. These perturbations culminated in the observation of four clear magnetospheric flux transfer events (FTEs) adjacent to the magnetopause, together with a highly-structured magnetopause boundary layer containing related field features. Furthermore, clear FTEs were observed later in the magnetosheath. The magnetospheric FTEs were of essentially the same form as the original "flux erosion events" observed in HEOS-2 data at a similar location and under similar interplanetary conditions by Haerendel et al. (1978). We show that the nature of the magnetic perturbations in these events is consistent with the formation of open flux tubes connected to the northern polar ionosphere via pulsed reconnection in the dusk sector magnetopause. The magnetic footprint of the Cluster spacecraft during the boundary passage is shown to map centrally within the fields-of-view of the CUTLASS SuperDARN radars, and to pass across the field-aligned beam of the EISCAT Svalbard radar (ESR) system. It is shown that both the ionospheric flow and the backscatter power in the CUTLASS data pulse are in synchrony with the magnetospheric FTEs and boundary layer structures at the latitude of the Cluster footprint. These flow and power features are subsequently found to propagate poleward, forming classic "pulsed ionospheric flow" and "poleward-moving radar auroral form" structures at higher latitudes. The combined Cluster-CUTLASS observations thus represent a direct demonstration of the coupling of momentum and energy into the magnetosphere-ionosphere system via pulsed magnetopause reconnection. The ESR observations also reveal the nature of the structured and variable polar ionosphere produced by the structured and time-varying precipitation and flow.Key words. Ionosphere (auroral ionosphere) Magentospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions)
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Grishanov, N. I., M. A. Raupp, A. F. D. Loula, and J. Pereira Neto. "Dispersion equations for field-aligned cyclotron waves in axisymmetric magnetospheric plasmas." Annales Geophysicae 24, no. 2 (March 23, 2006): 589–601. http://dx.doi.org/10.5194/angeo-24-589-2006.
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Abstract. In this paper, we derive the dispersion equations for field-aligned cyclotron waves in two-dimensional (2-D) magnetospheric plasmas with anisotropic temperature. Two magnetic field configurations are considered with dipole and circular magnetic field lines. The main contribution of the trapped particles to the transverse dielectric permittivity is estimated by solving the linearized Vlasov equation for their perturbed distribution functions, accounting for the cyclotron and bounce resonances, neglecting the drift effects, and assuming the weak connection of the left-hand and right-hand polarized waves. Both the bi-Maxwellian and bi-Lorentzian distribution functions are considered to model the ring current ions and electrons in the dipole magnetosphere. A numerical code has been developed to analyze the dispersion characteristics of electromagnetic ion-cyclotron waves in an electron-proton magnetospheric plasma with circular magnetic field lines, assuming that the steady-state distribution function of the energetic protons is bi-Maxwellian. As in the uniform magnetic field case, the growth rate of the proton-cyclotron instability (PCI) in the 2-D magnetospheric plasmas is defined by the contribution of the energetic ions/protons to the imaginary part of the transverse permittivity elements. We demonstrate that the PCI growth rate in the 2-D axisymmetric plasmasphere can be significantly smaller than that for the straight magnetic field case with the same macroscopic bulk parameters.
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Varela, J., V. Réville, A. S. Brun, P. Zarka, and F. Pantellini. "Effect of the exoplanet magnetic field topology on its magnetospheric radio emission." Astronomy & Astrophysics 616 (August 2018): A182. http://dx.doi.org/10.1051/0004-6361/201732091.
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Context. The magnetized wind from stars that impact exoplanets should lead to radio emissions. According to the scaling laws derived in the solar system, the radio emission should depend on the stellar wind, interplanetary magnetic field, and topology of the exoplanet magnetosphere. Aims. The aim of this study is to calculate the dissipated power and subsequent radio emission from exoplanet magnetospheres with different topologies perturbed by the interplanetary magnetic field and stellar wind, to refine the predictions from scaling laws, and to prepare the interpretation of future radio detections. Methods. We use the magnetohydrodynamic (MHD) code PLUTO in spherical coordinates to analyze the total radio emission level resulting from the dissipation of the kinetic and magnetic (Poynting flux) energies inside the exoplanet’s magnetospheres. We apply a formalism to infer the detailed contribution in the exoplanet radio emission on the exoplanet’s day side and magnetotail. The model is based on Mercury-like conditions, although the study results are extrapolated to exoplanets with stronger magnetic fields, providing the lower bound of the radio emission. Results. The predicted dissipated powers and resulting radio emissions depend critically on the exoplanet magnetosphere topology and interplanetary magnetic field (IMF) orientation. The radio emission on the exoplanet’s night and day sides should thus contain information on the exoplanet magnetic field topology. In addition, if the topology of an exoplanet magnetosphere is known, the radio emission measurements can be used as a proxy of the instantaneous dynamic pressure of the stellar wind, IMF orientation, and intensity.
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Lepidi, S., P. Francia, U. Villante, A. Meloni, A. J. Lazarus, and R. P. Lepping. "The Earth's passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions." Annales Geophysicae 17, no. 10 (October 31, 1999): 1245–50. http://dx.doi.org/10.1007/s00585-999-1245-4.
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Abstract. An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L'Aquila, Italy) station during the Earth's passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth's magnetosphere. Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetosphere interactions)
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Takasao, Shinsuke, Kengo Tomida, Kazunari Iwasaki, and Takeru K. Suzuki. "Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around the Star." Astrophysical Journal 941, no. 1 (December 1, 2022): 73. http://dx.doi.org/10.3847/1538-4357/ac9eb1.
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Abstract We perform three-dimensional (3D) magnetohydrodynamic simulations of magnetospheric accretion in a T Tauri star to study the accretion and wind structures in the close vicinity of the star. The gas accreting onto the star consists of the gas from the magnetospheric boundary and the failed disk winds. The accreting gas is commonly found as a multi-column accretion, which is consistent with observations. A significant fraction of the angular momentum of the accreting flows is removed by the magnetic fields of conical disk winds and turbulent failed winds inside and near the magnetosphere. As a result, the accretion torque is significantly reduced compared to the simple estimation based on the mass accretion rate. The stellar spin affects the time variability of the conical disk wind by changing the stability condition of the magnetospheric boundary. However, the time-averaged magnetospheric radius only weakly depends on the stellar spin, which is unlike the prediction of classical theories that the stellar spin controls the magnetospheric radius through the magnetic torque. The ratio of the toroidal to the poloidal field strengths at the magnetospheric boundary, which is a key parameter for the magnetic torque, is also insensitive to the spin; it is rather determined by the disk dynamics. Considering newly found 3D effects, we obtain a scaling relation of the magnetospheric radius very similar to the Ghosh & Lamb relation from the steady angular momentum transport equation.
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Leonovich, A. S., D. A. Kozlov, and V. A. Pilipenko. "Magnetosonic resonance in a dipole-like magnetosphere." Annales Geophysicae 24, no. 8 (September 13, 2006): 2277–89. http://dx.doi.org/10.5194/angeo-24-2277-2006.
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Abstract. A theory of resonant conversion of fast magnetosonic (FMS) waves into slow magnetosonic (SMS) oscillations in a magnetosphere with dipole-like magnetic field has been constructed. Monochromatic FMS waves are shown to drive standing (along magnetic field lines) SMS oscillations, narrowly localized across magnetic shells. The longitudinal and transverse structures, as well as spectrum of resonant SMS waves are determined. Frequencies of fundamental harmonics of standing SMS waves lie in the range of 0.1–1 mHz, and are about two orders of magnitude lower than frequencies of similar Alfvén field line resonance harmonics. This difference makes an effective interaction between these MHD modes impossible. The amplitude of SMS oscillations rapidly decreases along the field lines from the magnetospheric equator towards the ionosphere. In this context, magnetospheric SMS oscillations cannot be observed on the ground, and the ionosphere does not play any role either in their generation or dissipation. The theory developed can be used to interpret the occurrence of compressional Pc5 waves in a quiet magnetosphere with a weak ring current.
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Delcourt, D. C., T. E. Moore, and M. C. H. Fok. "Ion dynamics during compression of Mercury's magnetosphere." Annales Geophysicae 28, no. 8 (August 3, 2010): 1467–74. http://dx.doi.org/10.5194/angeo-28-1467-2010.
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Abstract. Because of the small planetary magnetic field as well as proximity to the Sun that leads to enhanced solar wind pressure as compared to Earth, the magnetosphere of Mercury is very dynamical and at times subjected to prominent compression. We investigate the dynamics of magnetospheric ions during such compression events. Using three-dimensional single-particle simulations, we show that the electric field induced by the time varying magnetic field can lead to significant ion energization, up to several hundreds of eVs or a few keVs. This energization occurs in a nonadiabatic manner, being characterized by large enhancements of the ion magnetic moment and bunching in gyration phase. It is obtained when the ion cyclotron period is comparable to the field variation time scale. This condition for nonadiabatic heating is realized in distinct regions of space for ions with different mass-to-charge ratios. During compression of Mercury's magnetosphere, heavy ions originating from the planetary exosphere may be subjected to such an abrupt energization, leading to loading of the magnetospheric lobes with energetic material.
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Romanova, Marina M., M. Long, A. K. Kulkarni, R. Kurosawa, G. V. Ustyugova, A. K. Koldoba, and R. V. E. Lovelace. "MHD simulations of disk-star interaction." Proceedings of the International Astronomical Union 3, S243 (May 2007): 277–90. http://dx.doi.org/10.1017/s1743921307009635.
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AbstractWe discuss a number of topics relevant to disk-magnetosphere interaction and how numerical simulations illuminate them. The topics include: (1) disk-magnetosphere interaction and the problem of disk-locking; (2) the wind problem; (3) structure of the magnetospheric flow, hot spots at the star's surface, and the inner disk region; (4) modeling of spectra from 3D funnel streams; (5) accretion to a star with a complex magnetic field; (6) accretion through 3D instabilities; (7) magnetospheric gap and survival of protoplanets. Results of both 2D and 3D simulations are discussed.
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Feygin, F. Z., N. G. Kleimenova, O. A. Pokhotelov, M. Parrot, K. Prikner, K. Mursula, J. Kangas, and T. Pikkarainen. "Nonstationary pearl pulsations as a signature of magnetospheric disturbances." Annales Geophysicae 18, no. 5 (May 31, 2000): 517–22. http://dx.doi.org/10.1007/s00585-000-0517-9.
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Abstract. We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequencies. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric field based on the variation of the central frequency of pearl pulsations.Key words: Magnetospheric physics (magnetospheric configuration and dynamics; plasma waves and instabilities)
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Zhang, Y. C., C. Shen, Z. X. Liu, and Y. Narita. "Magnetic helicity of a flux rope in the magnetotail: THEMIS results." Annales Geophysicae 28, no. 9 (September 20, 2010): 1687–93. http://dx.doi.org/10.5194/angeo-28-1687-2010.
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Abstract. The magnetic field in many regions of magnetosphere has a complex topological structure. As a parameter to measure the topological complexity, the concept of magnetic helicity is a useful tool in magnetospheric physics. Here we present a case study of magnetic helicity in the flux rope (FR) in the near-Earth plasma sheet (PS) based on the in-situ observation from THEMIS for the first time. With the help of the Grad-Shafranov reconstruction technique, we determine the spatial distribution of magnetic field and evaluate the magnetic helicity in the flux rope. The conservation of magnetic helicity during multiple X-line reconnections and the transport of magnetic helicity between different magnetic field configurations are also discussed. The further application of helicity in magnetosphere will provide us more knowledge about the topologic property of the magnetic fields there and more attention should be paid to that.
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Pudovkin, M. I., B. P. Besser, and S. A. Zaitseva. "Magnetopause stand-off distance in dependence on the magnetosheath and solar wind parameters." Annales Geophysicae 16, no. 4 (April 30, 1998): 388–96. http://dx.doi.org/10.1007/s00585-998-0388-z.
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Abstract. A model of the magnetosheath structure proposed in a recent paper from the authors is extended to estimate the magnetopause stand-off distance from solar wind data. For this purpose, the relationship of the magnetopause location to the magnetosheath and solar wind parameters is studied. It is shown that magnetopause erosion may be explained in terms of the magnetosheath magnetic field penetration into the magnetosphere. The coefficient of penetration (the ratio of the magnetospheric magnetic field depression to the intensity of the magnetosheath magnetic field Bm⊥z=–Bmsin2Θ/2, is estimated and found approximately to equal 1. It is shown that having combined a magnetosheath model presented in an earlier paper and the magnetosheath field penetration model presented in this paper, it is possible to predict the magnetopause stand-off distance from solar wind parameters.Key words. Magnetospheric physics · Magnetopause · Cusp and boundary layers-Magnetosheath
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Tang, Binbin, Wenya Li, Chi Wang, Lei Dai, Yuri Khotyaintsev, Per-Arne Lindqvist, Robert Ergun, et al. "Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin–Helmholtz waves." Annales Geophysicae 36, no. 3 (June 15, 2018): 879–89. http://dx.doi.org/10.5194/angeo-36-879-2018.
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Abstract. We report an ion-scale magnetic flux rope (the size of the flux rope is ∼ 8.5 ion inertial lengths) at the trailing edge of Kelvin–Helmholtz (KH) waves observed by the Magnetospheric Multiscale (MMS) mission on 27 September 2016, which is likely generated by multiple X-line reconnection. The currents of this flux rope are highly filamentary: in the central flux rope, the current flows are mainly parallel to the magnetic field, supporting a local magnetic field increase at about 7 nT, while at the edges the current filaments are predominantly along the antiparallel direction, which induce an opposing field that causes a significant magnetic depression along the axis direction (> 20 nT), meaning the overall magnetic field of this flux rope is depressed compared to the ambient magnetic field. Thus, this flux rope, accompanied by the plasma thermal pressure enhancement in the center, is referred to as a crater type. Intense lower hybrid drift waves (LHDWs) are found at the magnetospheric edge of the flux rope, and the wave potential is estimated to be ∼ 17 % of the electron temperature. Though LHDWs may be stabilized by the mechanism of electron resonance broadening, these waves could still effectively enable diffusive electron transports in the cross-field direction, corresponding to a local density dip. This indicates LHDWs could play important roles in the evolution of crater flux ropes. Keywords. Magnetospheric physics (magnetopause, cusp, and boundary layers; solar wind–magnetosphere interactions)
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Akasofu, S. I. "The relationship between the magnetosphere and magnetospheric/auroral substorms." Annales Geophysicae 31, no. 3 (March 4, 2013): 387–94. http://dx.doi.org/10.5194/angeo-31-387-2013.
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Abstract. On the basis of auroral and polar magnetic substorm studies, the relationship between the solar wind-magnetosphere dynamo (the DD dynamo) current and the substorm dynamo (the UL dynamo) current is studied. The characteristics of both the DD and UL currents reveal why auroral substorms consist of the three distinct phases after the input power ε is increased above 1018 erg s−1. (a) The growth phase; the magnetosphere can accumulate magnetic energy for auroral substorms, when the ionosphere cannot dissipate the power before the expansion phase. (b) The expansion phase; the magnetosphere releases the accumulated magnetic energy during the growth phase in a pulse-like manner in a few hours, because it tries to stabilize itself when the accumulated energy reaches to about 1023 erg s−1. (c) The recovery phase; the magnetosphere becomes an ordinary dissipative system after the expansion phase, because the ionosphere becomes capable of dissipating the power with the rate of 1018 ~ 1019 erg s−1. On the basis of the above conclusion, it is suggested that the magnetosphere accomplishes the pulse-like release process (resulting in spectacular auroral activities) by producing plasma instabilities in the current sheet, thus reducing the current. The resulting contraction of the magnetic field lines (expending the accumulated magnetic energy), together with break down of the "frozen-in" field condition at distances of less than 10 RE, establishes the substorm dynamo that generates an earthward electric field (Lui and Kamide, 2003; Akasofu, 2011). It is this electric field which manifests as the expansion phase. A recent satellite observation at a distance of as close as 8.1 RE by Lui (2011) seems to support strongly the occurrence of the chain of processes suggested in the above. It is hoped that although the concept presented here is very crude, it will serve in providing one way of studying the three phases of auroral substorms. In turn, a better understanding of auroral substorms will also be useful in studying the magnetosphere, because various auroral activities can be the visible guide for this endeavor.
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Nordheim, T. A., L. H. Regoli, C. D. K. Harris, C. Paranicas, K. P. Hand, and X. Jia. "Magnetospheric Ion Bombardment of Europa’s Surface." Planetary Science Journal 3, no. 1 (January 1, 2022): 5. http://dx.doi.org/10.3847/psj/ac382a.
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Abstract Jupiter’s moon Europa is exposed to constant bombardment by magnetospheric charged particles, which are expected to be a major source of physical and chemical surface modification. Here we have investigated the flux of magnetospheric ions at Europa’s surface by carrying out single particle tracing within realistic electromagnetic fields from multifluid magnetohydrodynamic simulations of the moon’s interaction with Jupiter’s magnetosphere. We find that magnetic field line draping and pileup leads to shielding and drastically reduced flux at low latitudes across Europa’s trailing (upstream) hemisphere. Furthermore, we find that magnetic induction within Europa’s subsurface ocean leads to additional shielding when the moon is located at high magnetic latitudes in Jupiter’s magnetosphere. Overall, we find that the high-latitude and polar regions on Europa receive the largest flux of magnetospheric ions. Both spacecraft and ground-based observations have previously identified a non–water ice surface species concentrated at Europa’s trailing (upstream) hemisphere, possibly hydrated sulfuric acid formed from radiolysis of water ice with implanted S ions. Our results demonstrate that the S ion flux across Europa’s equatorial trailing (upstream) hemisphere is strongly reduced, possibly indicating that the formation of the observed non–water ice species is controlled primarily by energy input from magnetospheric electrons, rather than the flux of S ions. We find that that O and S ions at >1 MeV energies have nearly uniform access to the surface, while energetic protons in this energy range are constrained to a “bull’s-eye” centered on the trailing (upstream) hemisphere.
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Dunlop, M. W., A. Balogh, P. Cargill, R. C. Elphic, K. H. Fornaçon, E. Georgescu, and F. Sedgemore-Schulthess. "Cluster observes the Earth’s magnetopause: coordinated four-point magnetic field measurements." Annales Geophysicae 19, no. 10/12 (September 30, 2001): 1449–60. http://dx.doi.org/10.5194/angeo-19-1449-2001.
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Abstract. The four-spacecraft Cluster mission has provided high-time resolution measurements of the magnetic field from closely maintained separation distances (200–600 km). Four-point coverage of the Earth’s magnetopause began on the 9 and 10 November 2000 when all spacecraft first exited the dusk-side magnetosphere at about 19:00 LT, providing extensive coverage of the near flank magnetosheath and magnetopause boundary layer on re-entry to the magnetosphere. The traversals on this occasion were caused by the arrival of an intense CME at the Earth, which produced a large compression of the magnetopause and high magnetic activity. The magnetopause traversals represent an unprecedented data set, allowing detailed analysis of the local magnetic structure (gradients) and dynamics of the magnetopause boundary. By performing minimum variance analysis (MVA) on the magnetic field data from all four spacecraft, we demonstrate that the magnetopause was planar on the scale of the spacecraft separation scales and that the transverse scale size of the magnetopause boundary layer was 1000–1100 km. We also show that the motion of the boundary (defined by the magnetic shear at the current layer), is changing over the sequence of spacecraft crossings so that acceleration of the magnetopause can be very high in this region of the magnetosphere. Indeed, the magnetopause speed reaches the order of 300 km/s in response to the arrival of the interplanetary shock. Using MVA coordinates, we have identified a number of magnetospheric and magnetosheath FTE signatures, which are sampled simultaneously by all spacecraft at different distances from and on either side of the magnetopause. The signatures show a variation of scale with distance from the boundary.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers) Space plasma physics (discontinuities; magnetic reconnection)
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Biktash, L. Z. "Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms." Annales Geophysicae 22, no. 9 (September 23, 2004): 3195–202. http://dx.doi.org/10.5194/angeo-22-3195-2004.
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Abstract. The equatorial ionosphere parameters, Kp, Dst, AU and AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the geomagnetic activity effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict near 70% of scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind - magnetosphere - ionosphere during magnetic storms have progressed greatly. According to present view, the intensity of the electric fields and currents at the polar regions, as well as the magnetospheric ring current intensity, are strongly dependent on the variations of the interplanetary magnetic field. The magnetospheric ring current cannot directly penetrate the equatorial ionosphere and because of this difficulties emerge in explaining its relation to scintillation activity. On the other hand, the equatorial scintillations can be observed in the absence of the magnetospheric ring current. It is shown that in addition to Aarons' criteria for the prediction of the ionospheric scintillations, models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind.
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Antonova, E. E., I. P. Kirpichev, I. L. Ovchinnikov, K. G. Orlova, and M. V. Stepanova. "High latitude magnetospheric topology and magnetospheric substorm." Annales Geophysicae 27, no. 10 (October 28, 2009): 4069–73. http://dx.doi.org/10.5194/angeo-27-4069-2009.
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Abstract. This study is focused on the problem of the localization of substorm expansion onset. In this context, the high latitude topology of transverse magnetospheric currents has been analyzed. This study has included the radial distribution of plasma pressure near noon, obtained using the THEMIS-B satellite data, the daytime compression of magnetic field lines and the existence of magnetic field minima far from the equatorial plane, given by all geomagnetic field models. As a result, the dayside integral transverse currents at the geocentric distances 7–10 RE has been estimated. It is suggested, that nightside transverse currents at geocentric distances ~7–10 RE are closed inside the magnetosphere and with dayside transverse currents form surrounding the Earth current system (cut ring current or CRC) which topologically is the high latitude continuation of ordinary ring current. A possibility of localization of substorm expansion onset at the nighside CRC region is analyzed using the experimental evidences that the onset is localized at geocentric distances <10 RE.
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Takasao, Shinsuke, Kengo Tomida, Kazunari Iwasaki, and Takeru K. Suzuki. "3D simulations of accretion onto a star: Fast funnel-wall accretion." Proceedings of the International Astronomical Union 14, A30 (August 2018): 138. http://dx.doi.org/10.1017/s1743921319003892.
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AbstractWe show the results of global 3D magnetohydrodynamics simulations of an accretion disk with a rotating, weakly magnetized central star (Takasao et al. 2018). The disk is threaded by a weak large-scale poloidal magnetic field. The central star has no strong stellar magnetosphere initially and is only weakly magnetized. We investigate the structure of the accretion flows from a turbulent accretion disk onto the star. Our simulations reveal that fast accretion onto the star at high latitudes is established even without a stellar magnetosphere. We find that the failed disk wind becomes the fast, high-latitude accretion as a result of angular momentum exchange mediated by magnetic fields. The rapid angular momentum exchange occurs well above the disk, where the Lorentz force that decelerates the rotational motion of gas can be comparable to the centrifugal force. Unlike the classical magnetospheric accretion model, fast accretion streams are not guided by magnetic fields of the stellar magnetosphere. Nevertheless, the accretion velocity reaches the free-fall velocity at the stellar surface owing to the efficient angular momentum loss at a distant place from the star. Our model can be applied to Herbig Ae/Be stars whose magnetic fields are generally not strong enough to form magnetospheres, and also provides a possible explanation why Herbig Ae/Be stars show indications of fast accretion.
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Eriksson, S., L. G. Blomberg, N. Ivchenko, T. Karlsson, and G. T. Marklund. "Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field." Annales Geophysicae 19, no. 6 (June 30, 2001): 649–53. http://dx.doi.org/10.5194/angeo-19-649-2001.
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Abstract. The cross-polar potential drop Φpc and the low-latitude asymmetric geomagnetic disturbance field, as indicated by the mid-latitude ASY-H magnetic index, are used to study the average magnetospheric response to the solar wind forcing for southward interplanetary magnetic field conditions. The state of the solar wind is monitored by the ACE spacecraft and the ionospheric convection is measured by the double probe electric field instrument on the Astrid-2 satellite. The solar wind-magnetosphere coupling is examined for 77 cases in February and from mid-May to mid-June 1999 by using the interplanetary magnetic field Bz component and the reconnection electric field. Our results show that the maximum correlation between Φpc and the reconnection electric field is obtained approximately 25 min after the solar wind has reached a distance of 11 RE from the Earth, which is the assumed average position of the magnetopause. The corresponding correlation for ASY-H shows two separate responses to the reconnection electric field, delayed by about 35 and 65 min, respectively. We suggest that the combination of the occurrence of a large magnetic storm on 18 February 1999 and the enhanced level of geomagnetic activity which peaks at Kp = 7- may explain the fast direct response of ASY-H to the solar wind at 35 min, as well as the lack of any clear secondary responses of Φpc to the driving solar wind at time delays longer than 25 min.Key words. Magnetospheric physics (solar wind-magnetosphere interactions; plasma convection) – Ionosphere (electric fields and currents)
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Belenkaya, Elena S., Igor I. Alexeev, and Marina S. Blokhina. "Modeling of Magnetospheres of Terrestrial Exoplanets in the Habitable Zone around G-Type Stars." Universe 8, no. 4 (April 8, 2022): 231. http://dx.doi.org/10.3390/universe8040231.
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Using a paraboloid model of an Earth-like exoplanetary magnetospheric magnetic field, developed from a model of the Earth, we investigate the magnetospheric structure of planets located in the habitable zone around G-type stars. Different directions of the stellar wind magnetic field are considered and the corresponding variations in the magnetospheric structure are obtained. It is shown that the exoplanetary environment significantly depends on stellar wind magnetic field orientation and that the parameters of magnetospheric current systems depend on the distance to the stand-off magnetopause point.
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Miller, M. Coleman, Frederick K. Lamb, and Russell J. Hamilton. "Electrodynamics of Disk-Accreting Magnetic Neutron Stars." International Astronomical Union Colloquium 142 (1994): 833–35. http://dx.doi.org/10.1017/s0252921100078179.
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AbstractWe have investigated the electrodynamics of magnetic neutron stars accreting from Keplerian disks and the implications for particle acceleration and γ-ray emission by such systems. We argue that the particle density in the magnetospheres of such stars is larger by orders of magnitude than the Goldreich-Julian density, so that the formation of vacuum gaps is unlikely. We show that even if the star rotates slowly, electromotive forces ( EMFs ) of order 1015 V are produced by the interaction of plasma in the accretion disk with the magnetic field of the neutron star. The resistance of the disk-magnetosphere-star circuit is small, and hence these EMFs drive very large conduction currents. Such large currents are likely to produce magnetospheric instabilities, such as relativistic double layers and reconnection events, that can accelerate electrons or ions to very high energies.Subject headings: acceleration of particles — accretion, accretion disks — MHD — stars: neutron
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Belenkaya, E. S., I. I. Alexeev, M. S. Blokhina, S. W. H. Cowley, S. V. Badman, V. V. Kalegaev, and M. S. Grigoryan. "IMF dependence of the open-closed field line boundary in Saturn's ionosphere, and its relation to the UV auroral oval observed by the Hubble Space Telescope." Annales Geophysicae 25, no. 5 (June 4, 2007): 1215–26. http://dx.doi.org/10.5194/angeo-25-1215-2007.
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Abstract. We study the dependence of Saturn's magnetospheric magnetic field structure on the interplanetary magnetic field (IMF), together with the corresponding variations of the open-closed field line boundary in the ionosphere. Specifically we investigate the interval from 8 to 30 January 2004, when UV images of Saturn's southern aurora were obtained by the Hubble Space Telescope (HST), and simultaneous interplanetary measurements were provided by the Cassini spacecraft located near the ecliptic ~0.2 AU upstream of Saturn and ~0.5 AU off the planet-Sun line towards dawn. Using the paraboloid model of Saturn's magnetosphere, we calculate the magnetospheric magnetic field structure for several values of the IMF vector representative of interplanetary compression regions. Variations in the magnetic structure lead to different shapes and areas of the open field line region in the ionosphere. Comparison with the HST auroral images shows that the area of the computed open flux region is generally comparable to that enclosed by the auroral oval, and sometimes agrees in detail with its poleward boundary, though more typically being displaced by a few degrees in the tailward direction.