Journal articles on the topic 'Magnetosphere dynamo'
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Lopez, R. E., V. G. Merkin, and J. G. Lyon. "The role of the bow shock in solar wind-magnetosphere coupling." Annales Geophysicae 29, no. 6 (June 25, 2011): 1129–35. http://dx.doi.org/10.5194/angeo-29-1129-2011.
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Abstract. In this paper we examine the role of the bow shock in coupling solar wind energy to the magnetosphere using global magnetohydrodynamic simulations of the solar wind-magnetosphere interaction with southward IMF. During typical solar wind conditions, there are two significant dynamo currents in the magnetospheric system, one in the high-latitude mantle region tailward of the cusp and the other in the bow shock. As the magnitude of the (southward) IMF increases and the solar wind becomes a low Mach number flow, there is a significant change in solar wind-magnetosphere coupling. The high-latitude magnetopause dynamo becomes insignificant compared to the bow shock and a large load appears right outside the magnetopause. This leaves the bow shock current as the only substantial dynamo current in the system, and the only place where a significant amount of mechanical energy is extracted from the solar wind. That energy appears primarily as electromagnetic energy, and the Poynting flux generated at the bow shock feeds energy back into the plasma, reaccelerating it to solar wind speeds. Some small fraction of that Poynting flux is directed into the magnetosphere, supplying the energy needed for magnetospheric dynamics. Thus during periods when the solar wind flow has a low Mach number, the main dynamo in the solar wind-magnetosphere system is the bow shock.
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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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Simon, P. A., and J. P. Legrand. "Dipole Field, Sunspot Cycle and Solar Dynamo." Symposium - International Astronomical Union 157 (1993): 97–106. http://dx.doi.org/10.1017/s0074180900173930.
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From the analysis of a series of data concerning phenomena taking place in the high corona, in the interplanetary medium and in the magnetosphere, we came to the conclusion that we have to take into consideration a two-component solar cycle in which, with a 5–6 yr delay, the cycle of the dipole component of the solar magnetic field and the following sunspot cycle are closely correlated. In order to show the new mechanisms to incorporate into a model of a two-component solar cycle, we discuss several other relevant solar data.
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Egi, Masashi, Akira Tomimatsu, and Masaaki Takahashi. "8.13. The dynamo effect in magnetohydrodynamic accretion onto a rotating black hole." Symposium - International Astronomical Union 184 (1998): 369–70. http://dx.doi.org/10.1017/s0074180900085260.
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A rotaing black hole has interesting features which can't be seen in nonrotating cases. The most characteristic one is to induce differential rotaions at angular velocity ω in inertial frames. Astrophysically it might have various impacts on its surrounding accretion plasmas. In a stationary and axisymmetric magnetohydrodynamic picture, it enables to directly extract the rotation energy of the black hole in the form of the outgoing Poynting flux. This process needs a condition ΩF(ΩH – ΩF) > 0 on the horizon r = rH, where ΩH ≡ ω|rH, and ΩF is the angular velocity of magnetosphere. However, it is not so clear how the extracted energy activates the magnetosphere. Recently, Kahnna and Camenzind (KC 1994,1995) proposed a possibility of a self-excitation mechanism of the electromagnetic fields, supported by a coupling between ω and the angular velocity of plasma Ω, through the magnetic diffusivity e of accretion plasmas. They called it ωΩ dynamo and tried to confirm this effect by numerical simulations. However no such growing cases were found in the initial conditions employed in the simulations (Brandenbrug 1996, KC 1996).
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Amory-Mazaudier, Christine. "Magnetic Signatures of Large-Scale Electric Currents in the Earth’s Environment at Middle and Low Latitudes." Atmosphere 13, no. 10 (October 17, 2022): 1699. http://dx.doi.org/10.3390/atmos13101699.
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The purpose of space weather is the systemic study of the Sun–Earth system, in order to determine the impact of solar events on the electromagnetic environment of the Earth. This article proposes a new transdisciplinary approach of the Sun–Earth system based on the universal physical process of the dynamo. The dynamo process is based on two important parameters of the different plasmas of the Sun–Earth system, the motion and the magnetic field. There are four permanent dynamos in the Sun–Earth system: the solar dynamo, the Earth dynamo, the solar wind-magnetosphere dynamo, and the ionospheric dynamo. These four permanent dynamos are part of different scientific disciplines. This transdisciplinary approach links all of these dynamos in order to understand the variations in the Earth’s magnetic field. During a magnetic disturbed period, other dynamos exist. We focused on the ionospheric disturbed dynamo generated by Joule energy dissipated in the high latitude ionosphere during magnetic storms. Joule heating disrupts the circulation of thermospheric winds and in turn generates disturbances in the Earth’s magnetic field. This systemic approach makes it possible to understand magnetic disturbances previously not well understood.
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Hellier, Coel. "Disc–magnetosphere interactions in cataclysmic variable stars." Proceedings of the International Astronomical Union 3, S243 (May 2007): 325–36. http://dx.doi.org/10.1017/s1743921307009684.
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AbstractI review, from an observational perspective, the interactions of accretion discs with magnetic fields in cataclysmic variable stars. I start with systems where the accretion flows via a stream, and discuss the circumstances in which the stream forms into an accretion disc, pointing to stars which are close to this transition. I then turn to disc-fed systems and discuss what we know about how material threads on to field lines, as deduced from the pattern of accretion footprints on the white dwarf. I discuss whether distortions of the field lines are related to accretion torques and the changing spin periods of the white dwarfs. I also review the effect on the disc–magnetosphere interaction of disc-instability outbursts. Lastly, I discuss the temporary, dynamo-driven magnetospheres thought to occur in dwarf-nova outbursts, and whether slow-moving waves are excited at the inner edges of the disc.
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Belenkaya, Elena, and Igor Alexeev. "Sliding Contacts in Planetary Magnetospheres." Symmetry 13, no. 2 (February 7, 2021): 283. http://dx.doi.org/10.3390/sym13020283.
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In the planetary magnetospheres there are specific places connected with velocity breakdown, reconnection, and dynamo processes. Here we pay attention to sliding layers. Sliding layers are formed in the ionosphere, on separatrix surfaces, at the magnetopauses and boundaries of stellar astrospheres, and at the Alfvén radius in the equatorial magnetosphere of rapidly rotating strongly magnetized giant planets. Although sliding contacts usually occur in thin local layers, their influence on the global structure of the surrounding space is very great. Therefore, they are associated with non-local processes that play a key role on a large scale. There can be an exchange between different forms of energy, a generation of strong field-aligned currents and emissions, and an amplification of magnetic fields. Depending on the conditions in the magnetosphere of the planet/exoplanet and in the flow of magnetized plasma passing it, different numbers of sliding layers with different configurations appear. Some are associated with regions of auroras and possible radio emissions. The search for planetary radio emissions is a current task in the detection of exoplanets.
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Poplavsky, A. L., O. P. Kuznechik, and N. I. Stetyukevich. "Large-scale dynamo of accretion disks around supermassive nonrotating black holes." Serbian Astronomical Journal, no. 173 (2006): 49–55. http://dx.doi.org/10.2298/saj0673049p.
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In this paper one presents an analytical model of accretion disk magnetosphere dynamics around supermassive nonrotating black holes in the centers of active galactic nuclei. Based on general relativistic equations of magneto hydrodynamics, the nonstationary solutions for time-dependent dynamo action in the accretion disks, spatial and temporal distribution of magnetic field are found. It is shown that there are two distinct stages of dynamo process: the transient and the steady-state regimes, the induction of magnetic field at t > 6:6665 x 1011GM/c3 s becomes stationary, magnetic field is located near the innermost stable circular orbit, and its value rises up to ~ 105 G. Applications of such systems with nonrotating black holes in real active galactic nuclei are discussed.
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Dimant, Y. S., and M. M. Oppenheim. "Interaction of plasma cloud with external electric field in lower ionosphere." Annales Geophysicae 28, no. 3 (March 11, 2010): 719–36. http://dx.doi.org/10.5194/angeo-28-719-2010.
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Abstract. In the auroral lower-E and upper-D region of the ionosphere, plasma clouds, such as sporadic-E layers and meteor plasma trails, occur daily. Large-scale electric fields, created by the magnetospheric dynamo, will polarize these highly conducting clouds, redistributing the electrostatic potential and generating anisotropic currents both within and around the cloud. Using a simplified model of the cloud and the background ionosphere, we develop the first self-consistent three-dimensional analytical theory of these phenomena. For dense clouds, this theory predicts highly amplified electric fields around the cloud, along with strong currents collected from the ionosphere and circulated through the cloud. This has implications for the generation of plasma instabilities, electron heating, and global MHD modeling of magnetosphere-ionosphere coupling via modifications of conductances induced by sporadic-E clouds.
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von Rekowski, B., and A. Brandenburg. "Outflows and accretion in a star-disc system with stellar magnetosphere and disc dynamo." Astronomy & Astrophysics 420, no. 1 (May 14, 2004): 17–32. http://dx.doi.org/10.1051/0004-6361:20034065.
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Suji, K. J., and P. R. Prince. "Energetics of Magnetosphere-Ionosphere system during Main Phase of Intense Geomagnetic Storms over three Solar Cycles." Proceedings of the International Astronomical Union 13, S340 (February 2018): 69–70. http://dx.doi.org/10.1017/s1743921318001928.
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AbstractSolar wind kinetic energy gets transferred into the Earth’s magnetosphere as a result of dynamo action between magnetosphere and solar wind. Energy is then dissipated among various dissipation channels in the MI system. In the present study, energetics of 59 intense geomagnetic storms are analyzed for the period between 1986 and 2015, which covers the three consecutive solar cycles SC 22, 23 and 24. The average solar wind energy impinging the MI system is estimated using Epsilon parameter, the coupling function. Moreover, the relative importance of different energy sinks in the MI system are quantified and is found that more than 60% of solar wind energy is dissipated in the form of ionospheric Joule heating.
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Tomei, Niccolò, Luca Del Zanna, Matteo Bugli, and Niccolò Bucciantini. "Are GRMHD Mean-Field Dynamo Models of Thick Accretion Disks SANE?" Universe 7, no. 8 (July 23, 2021): 259. http://dx.doi.org/10.3390/universe7080259.
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The remarkable results by the Event Horizon Telescope collaboration concerning the emission from M87* and, more recently, its polarization properties, require an increasingly accurate modeling of the plasma flows around the accreting black hole. Radiatively inefficient sources such as M87* and Sgr A* are typically modeled with the SANE (standard and normal evolution) paradigm, if the accretion dynamics is smooth, or with the MAD (magnetically arrested disk) paradigm, if the black hole’s magnetosphere reacts by halting the accretion sporadically, resulting in a highly dynamical process. While the recent polarization studies seem to favor MAD models, this may not be true for all sources, and SANE accretion surely still deserves attention. In this work, we investigate the possibility of reaching the typical degree of magnetization and other accretion properties expected for SANE disks by resorting to the mean-field dynamo process in axisymmetric GRMHD simulations, which are supposed to mimic the amplifying action of an unresolved magnetorotational instability-driven turbulence. We show that it is possible to reproduce the main diagnostics present in the literature by starting from very unfavorable initial configurations, such as a purely toroidal magnetic field with negligible magnetization.
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Kabin, K., M. H. Heimpel, R. Rankin, J. M. Aurnou, N. Gómez-Pérez, J. Paral, T. I. Gombosi, T. H. Zurbuchen, P. L. Koehn, and D. L. DeZeeuw. "Global MHD modeling of Mercury's magnetosphere with applications to the MESSENGER mission and dynamo theory." Icarus 195, no. 1 (May 2008): 1–15. http://dx.doi.org/10.1016/j.icarus.2007.11.028.
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Korth, H., B. J. Anderson, H. U. Frey, and C. L. Waters. "High-latitude electromagnetic and particle energy flux during an event with sustained strongly northward IMF." Annales Geophysicae 23, no. 4 (June 3, 2005): 1295–310. http://dx.doi.org/10.5194/angeo-23-1295-2005.
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Abstract. We present a case study of a prolonged interval of strongly northward orientation of the interplanetary magnetic field on 16 July 2000, 16:00-19:00 UT to characterize the energy exchange between the magnetosphere and ionosphere for conditions associated with minimum solar wind-magnetosphere coupling. With reconnection occurring tailward of the cusp under northward IMF conditions, the reconnection dynamo should be separated from the viscous dynamo, presumably driven by the Kelvin-Helmholtz (KH) instability. Thus, these conditions are also ideal for evaluating the contribution of a viscous interaction to the coupling process. We derive the two-dimensional distribution of the Poynting vector radial component in the northern sunlit polar ionosphere from magnetic field observations by the constellation of Iridium satellites together with drift meter and magnetometer observations from the Defense Meteorological Satellite Program (DMSP) F13 and F15 satellites. The electromagnetic energy flux is then compared with the particle energy flux obtained from auroral images taken by the far-ultraviolet (FUV) instrument on the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft. The electromagnetic energy input to the ionosphere of 51 GW calculated from the Iridium/DMSP observations is eight times larger than the 6 GW due to particle precipitation all poleward of 78° MLAT. This result indicates that the energy transport is significant, particularly as it is concentrated in a small region near the magnetic pole, even under conditions traditionally considered to be quiet and is dominated by the electromagnetic flux. We estimate the contributions of the high and mid-latitude dynamos to both the Birkeland currents and electric potentials finding that high-latitude reconnection accounts for 0.8 MA and 45kV while we attribute <0.2MA and ~5kV to an interaction at lower latitudes having the sense of a viscous interaction. Given that these conditions are ideal for the occurrence of the KH instability at the magnetopause and hence the viscous interaction, this result suggests that the viscous interaction is a small contributor to coupling solar wind energy to the magnetosphere-ionosphere system.
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Buchert, Stephan C. "Entangled dynamos and Joule heating in the Earth's ionosphere." Annales Geophysicae 38, no. 5 (September 24, 2020): 1019–30. http://dx.doi.org/10.5194/angeo-38-1019-2020.
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Abstract. The Earth's neutral atmosphere is the driver of the well-known solar quiet (Sq) and other magnetic variations observed for more than 100 years. Yet the understanding of how the neutral wind can accomplish a dynamo effect has been incomplete. A new viable model is presented where a dynamo effect is obtained only in the case of winds perpendicular to the magnetic field B that do not map along B. Winds where u×B is constant have no effect. We identify Sq as being driven by wind differences at magnetically conjugate points and not by a neutral wind per se. The view of two different but entangled dynamos is favoured, with some conceptual analogy to quantum mechanical states. Because of the large preponderance of the neutral gas mass over the ionized component in the Earth's ionosphere, the dominant effect of the plasma adjusting to the winds is Joule heating. The amount of global Joule heating power from Sq is estimated, with uncertainties, to be much lower than Joule heating from ionosphere–magnetosphere coupling at high latitudes in periods of strong geomagnetic activity. However, on average both contributions could be relatively comparable. The global contribution of heating by ionizing solar radiation in the same height range should be 2–3 orders of magnitude larger.
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Tarduno, John A., Rory D. Cottrell, Kristin Lawrence, Richard K. Bono, Wentao Huang, Catherine L. Johnson, Eric G. Blackman, et al. "Absence of a long-lived lunar paleomagnetosphere." Science Advances 7, no. 32 (August 2021): eabi7647. http://dx.doi.org/10.1126/sciadv.abi7647.
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Determining the presence or absence of a past long-lived lunar magnetic field is crucial for understanding how the Moon’s interior and surface evolved. Here, we show that Apollo impact glass associated with a young 2 million–year–old crater records a strong Earth-like magnetization, providing evidence that impacts can impart intense signals to samples recovered from the Moon and other planetary bodies. Moreover, we show that silicate crystals bearing magnetic inclusions from Apollo samples formed at ∼3.9, 3.6, 3.3, and 3.2 billion years ago are capable of recording strong core dynamo–like fields but do not. Together, these data indicate that the Moon did not have a long-lived core dynamo. As a result, the Moon was not sheltered by a sustained paleomagnetosphere, and the lunar regolith should hold buried 3He, water, and other volatile resources acquired from solar winds and Earth’s magnetosphere over some 4 billion years.
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Vilela, Conrad, John Southworth, and Carlos del Burgo. "Stellar Magnetism and starspots: the implications for exoplanets." Proceedings of the International Astronomical Union 9, S302 (August 2013): 247–50. http://dx.doi.org/10.1017/s1743921314002208.
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AbstractStellar variability induced by starspots can hamper the detection of exoplanets and bias planet property estimations. These features can also be used to study star-planet interactions as well as inferring properties from the underlying stellar dynamo. However, typical techniques, such as ZDI, are not possible for most host-stars. We present a robust method based on spot modelling to map the surface of active star allowing us to statistically study the effects and interactions of stellar magnetism with transiting exoplanets. The method is applied to the active Kepler-9 star where we find small evidence for a possible interaction between planet and stellar magnetosphere which leads to a 2:1 resonance between spot rotation and orbital period.
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Hairston, M., N. Maruyama, W. R. Coley, and R. Stoneback. "Storm-time meridional flows: a comparison of CINDI observations and model results." Annales Geophysicae 32, no. 6 (June 17, 2014): 659–68. http://dx.doi.org/10.5194/angeo-32-659-2014.
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Abstract. During a large geomagnetic storm, the electric field from the polar ionosphere can expand far enough to affect the mid-latitude and equatorial electric fields. These changes in the equatorial zonal electric field, called the penetration field, will cause changes in the meridional ion flows that can be observed by radars and spacecraft. In general this E × B ion flow near the equator caused by the penetration field during undershielding conditions will be upward on the dayside and downward on the nightside of the Earth. Previous analysis of the equatorial meridional flows observed by CINDI instrument on the C/NOFS spacecraft during the 26 September 2011 storm showed that all of the response flows on the dayside were excess downward flows instead of the expected upward flows. These observed storm-time responses are compared to a prediction from a physics-based coupled model of thermosphere–ionosphere–inner-magnetosphere in an effort to explain these observations. The model results suggest that the equatorial downward flow could be attributed to a combined effect of the overshielding and disturbance dynamo processes. However, some discrepancy between the model and observation indicates a need for improving our understanding of how sensitive the equatorial electric field is to various model input parameters that describe the magnetosphere–ionosphere coupling processes.
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Carpenter, D. L., and J. Lemaire. "The Plasmasphere Boundary Layer." Annales Geophysicae 22, no. 12 (December 22, 2004): 4291–98. http://dx.doi.org/10.5194/angeo-22-4291-2004.
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Abstract. As an inner magnetospheric phenomenon the plasmapause region is of interest for a number of reasons, one being the occurrence there of geophysically important interactions between the plasmas of the hot plasma sheet and of the cool plasmasphere. There is a need for a conceptual framework within which to examine and discuss these interactions and their consequences, and we therefore suggest that the plasmapause region be called the Plasmasphere Boundary Layer, or PBL. Such a term has been slow to emerge because of the complexity and variability of the plasma populations that can exist near the plasmapause and because of the variety of criteria used to identify the plasmapause in experimental data. Furthermore, and quite importantly in our view, a substantial obstacle to the consideration of the plasmapause region as a boundary layer has been the longstanding tendency of textbooks on space physics to limit introductory material on the plasmapause phenomenon to zeroth order descriptions in terms of ideal MHD theory, thus implying that the plasmasphere is relatively well understood. A textbook may introduce the concept of shielding of the inner magnetosphere from perturbing convection electric fields, but attention is not usually paid to the variety of physical processes reported to occur in the PBL, such as heating, instabilities, and fast longitudinal flows, processes which must play roles in plasmasphere dynamics in concert with the flow regimes associated with the major dynamo sources of electric fields. We believe that through the use of the PBL concept in future textbook discussions of the plasmasphere and in scientific communications, much progress can be made on longstanding questions about the physics involved in the formation of the plasmapause and in the cycles of erosion and recovery of the plasmasphere. Key words. Magnetospheric physics (plasmasphere; plasma convection; MHD waves and instabilities)
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Dehingia, Bharat. "ALTERNATING -SPACE TECHNOLOGY FOR MARS." International Journal of Scientific & Engineering Research 14, no. 1 (January 25, 2023): 730–44. http://dx.doi.org/10.14299/ijser.2023.01.03.
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Discovery of Phobos by Asaph Hall in 1877 is a key signature to study alternating space technology for Mars.Phobos is the largest and closest moon-let of Mars.Mars has a weak magnetic strength to shield harmful radiation and solar wind.To terraform Mars like our Earth we need 48 sextillion joule of seismic energy.The aim of this study is to deploy Phobos at a true anomaly of 300 degree of Mars. Phobos has 48 septillion joule of kinetic energy above a mean zenith of 6000 km.We can convert this kinetic energy into seismic energy by deploying phobos at a significant coordinate near the equator of Mars.Hence it will create a Mars-quack of amplitude 51.84 for a time interval of 5 years to terraform.It gives an outcome of convection current about 669A during my simulation.It was enough to drive the tectonic plates of Mars to enlarge the magnetosphere as well as to erupt Olympus mons and Elysium mons.During this simulation I also noticed that it activated the Dynamo effect of Mars accordingly in the direction of Magnetic field lines.The presence of magnetosphere is a responsible discovery to sustain humanity on Mars before the age of Asteroids and coronal mass ejection from our Sun.The simulation showed that after volcanic eruption on Mars ,air-aqua-atmosphere came into existence naturally. After deployment of Phobos , Deimos orbits Mars to continue it's binary relation like our Earth -Moon system.
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Matsui, H., P. A. Puhl-Quinn, V. K. Jordanova, Y. Khotyaintsev, P. A. Lindqvist, and R. B. Torbert. "Derivation of inner magnetospheric electric field (UNH-IMEF) model using Cluster data set." Annales Geophysicae 26, no. 9 (September 23, 2008): 2887–98. http://dx.doi.org/10.5194/angeo-26-2887-2008.
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Abstract. We derive an inner magnetospheric electric field (UNH-IMEF) model at L=2–10 using primarily Cluster electric field data for more than 5 years between February 2001 and October 2006. This electric field data set is divided into several ranges of the interplanetary electric field (IEF) values measured by ACE. As ring current simulations which require electric field as an input parameter are often performed at L=2–6.6, we have included statistical results from ground radars and low altitude satellites inside the perigee of Cluster in our data set (L~4). Electric potential patterns are derived from the average electric fields by solving an inverse problem. The electric potential pattern for small IEF values is probably affected by the ionospheric dynamo. The magnitudes of the electric field increase around the evening local time as IEF increases, presumably due to the sub-auroral polarization stream (SAPS). Another region with enhanced electric fields during large IEF periods is located around 9 MLT at L>8, which is possibly related to solar wind-magnetosphere coupling. Our potential patterns are consistent with those derived from self-consistent simulations. As the potential patterns can be interpolated/extrapolated to any discrete IEF value within measured ranges, we thus derive an empirical electric potential model. The performance of the model is evaluated by comparing the electric field derived from the model with original one measured by Cluster and mapped to the equator. The model is open to the public through our website.
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Brain, David A. "The Response of the Martian Atmosphere to Space Weather." Proceedings of the International Astronomical Union 13, S335 (July 2017): 114–20. http://dx.doi.org/10.1017/s1743921317010924.
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AbstractMars lacks a global dynamo magnetic field to shield it from the solar wind and solar storms, so may be especially sensitive to changing space weather compared to Earth. Inputs from the Sun and solar wind have been measured continuously at Mars for 20 years, and intermittently for more than 50 years. Observations of the influence of the variable space weather at Mars include compression and reconfiguration of the magnetosphere in response to solar storms, increased likelihood of aurora and increased auroral electron energies, increased particle precipitation and ionospheric densities during flare and energetic particle events, and increased ion escape during coronal mass ejection events. Continuing measurements at Mars provide a useful vantage point for studying space weather propagation into the heliosphere, and are providing insight into the evolution of the Martian atmosphere and the role that planetary magnetic fields play in helping planets to retain habitable conditions near their surface.
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Bolton, S. J. "The Juno Mission." Proceedings of the International Astronomical Union 6, S269 (January 2010): 92–100. http://dx.doi.org/10.1017/s1743921310007313.
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AbstractJuno is the next NASA New Frontiers mission which will launch in August 2011. The mission is a solar powered spacecraft scheduled to arrive at Jupiter in 2016 and be placed into polar orbit around Jupiter. The goal of the Juno mission is to explore the origin and evolution of the planet Jupiter. Juno's science themes include (1) origin, (2) interior structure, (3) atmospheric composition and dynamics, and (4) polar magnetosphere and aurora. A total of nine instruments on-board provide specific measurements designed to investigate Juno's science themes. The primary objective of investigating the origin of Jupiter includes 1) determine Jupiter's internal mass distribution by measuring gravity with Doppler tracking, 2) determine the nature of its internal dynamo by measuring its magnetic fields with a magnetometer, and 3) determine the deep composition (in particular the global water abundance) and dynamics of the sub-cloud atmosphere around Jupiter, by measuring its thermal microwave emission.
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Heikkila, W. J. "Comment on Lockwood and Davis, "On the longitudinal extent of magnetopause reconnection pulses"." Annales Geophysicae 17, no. 2 (February 28, 1999): 173–77. http://dx.doi.org/10.1007/s00585-999-0173-7.
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Abstract. Lockwood and Davis (1996) present a concise description of magnetopause reconnection pulses, with the claimed support of three types of observations: (1) flux transfer events (FTE), (2) poleward-moving auroral forms on the dayside, and (3) steps in cusp ion dispersion characteristics. However, there are a number of errors and misconceptions in the paper that make their conclusions untenable. They do not properly take account of the fact that the relevant processes operate in the presence of a plasma. They fail to notice that the source of energy (a dynamo with E · J<0) must be close to the region of dissipation (the electrical load with E · J>0) in transient phenomena, since energy (or information) cannot travel faster than the group velocity of waves in the medium (here the Alfvén velocity VA). In short, Lockwood and Davis use the wrong contour in their attempt to evaluate the electromotive force (emf). This criticism goes beyond their article: a dynamo is not included in the usual definition of reconnection, only the reconnection load. Without an explicit source of energy in the assumed model, the idea of magnetic reconnection is improperly posed. Recent research has carried out a superposed epoch analysis of conditions near the dayside magnetopause and has found the dynamo and the load, both within the magnetopause current sheet. Since the magnetopause current is from dawn to dusk, the sign of E · J reflects the sign of the electric field. The electric field reverses, within the magnetopause; this can be discovered by an application of Lenz's law using the concept of erosion of the magnetopause. The net result is plasma transfer across the magnetopause to feed the low latitude boundary layer, at least partly on closed field lines, and viscous interaction as the mechanism by which solar wind plasma couples to the magnetosphere.
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Ayres, Thomas R. "Fossil Magnetospheres Confront Newborn Dynamos in the Rapid Braking Zone." Symposium - International Astronomical Union 215 (2004): 280–86. http://dx.doi.org/10.1017/s0074180900195725.
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Fast spinning Hertzsprung gap giants display super-rotational broadening of UV “hot” lines like Fe XXI λ1354 and C IV λ1548, with FWHM's up to twice that expected from the photospheric v sin i. This possibly is the result of extended fossil magnetospheres enveloping the gap giants, a new type of stellar corona. The magnetospheric phase is short-lived, however, as the rapidly evolving giants develop a competing dynamo-generated surface field in the so-called Rapid Braking Zone.
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Crinquand, B., B. Cerutti, G. Dubus, K. Parfrey, and A. Philippov. "Synthetic gamma-ray light curves of Kerr black hole magnetospheric activity from particle-in-cell simulations." Astronomy & Astrophysics 650 (June 2021): A163. http://dx.doi.org/10.1051/0004-6361/202040158.
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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. 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.
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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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Sandholt, P. E., C. J. Farrugia, and W. F. Denig. "Detailed dayside auroral morphology as a function of local time for southeast IMF orientation: implications for solar wind-magnetosphere coupling." Annales Geophysicae 22, no. 10 (November 3, 2004): 3537–60. http://dx.doi.org/10.5194/angeo-22-3537-2004.
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Abstract. In two case studies we elaborate on spatial and temporal structures of the dayside aurora within 08:00-16:00 magnetic local time (MLT) and discuss the relationship of this structure to solar wind-magnetosphere interconnection topology and the different stages of evolution of open field lines in the Dungey convection cycle. The detailed 2-D auroral morphology is obtained from continuous ground observations at Ny Ålesund (76° magnetic latitude (MLAT)), Svalbard during two days when the interplanetary magnetic field (IMF) is directed southeast (By>0; Bz<0). The auroral activity consists of the successive activations of the following forms: (i) latitudinally separated, sunward moving, arcs/bands of dayside boundary plasma sheet (BPS) origin, in the prenoon (08:00-11:00 MLT) and postnoon (12:00-16:00 MLT) sectors, within 70-75° MLAT, (ii) poleward moving auroral forms (PMAFs) emanating from the pre- and postnoon brightening events, and (iii) a specific activity appearing in the 07:00-10:00 MLT/75-80° MLAT during the prevailing IMF By>0 conditions. The pre- and postnoon activations are separated by a region of strongly attenuated auroral activity/intensity within the 11:00-12:00 MLT sector, often referred to as the midday gap aurora. The latter aurora is attributed to the presence of component reconnection at the subsolar magnetopause where the stagnant magnetosheath flow lead to field-aligned currents (FACs) which are of only moderate intensity. The much more active and intense aurorae in the prenoon (07:00-11:00 MLT) and postnoon (12:00-16:00 MLT) sectors originate in magnetopause reconnection events that are initiated well away from the subsolar point. The high-latitude auroral activity in the prenoon sector (feature iii) is found to be accompanied by a convection channel at the polar cap boundary. The associated ground magnetic deflection (DPY) is a Svalgaard-Mansurov effect. The convection channel is attributed to effective momentum transfer from the solar wind-magnetosphere dynamo in the high-latitude boundary layer (HBL), on the downstream side of the cusp.
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Namgaladze, A. A., M. Förster, and R. Y. Yurik. "Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model." Annales Geophysicae 18, no. 4 (April 30, 2000): 461–77. http://dx.doi.org/10.1007/s00585-000-0461-8.
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Abstract. Current theories of F-layer storms are discussed using numerical simulations with the Upper Atmosphere Model, a global self-consistent, time dependent numerical model of the thermosphere-ionosphere-plasmasphere-magnetosphere system including electrodynamical coupling effects. A case study of a moderate geomagnetic storm at low solar activity during the northern winter solstice exemplifies the complex storm phenomena. The study focuses on positive ionospheric storm effects in relation to thermospheric disturbances in general and thermospheric composition changes in particular. It investigates the dynamical effects of both neutral meridional winds and electric fields caused by the disturbance dynamo effect. The penetration of short-time electric fields of magnetospheric origin during storm intensification phases is shown for the first time in this model study. Comparisons of the calculated thermospheric composition changes with satellite observations of AE-C and ESRO-4 during storm time show a good agreement. The empirical MSISE90 model, however, is less consistent with the simulations. It does not show the equatorward propagation of the disturbances and predicts that they have a gentler latitudinal gradient. Both theoretical and experimental data reveal that although the ratio of [O]/[N2] at high latitudes decreases significantly during the magnetic storm compared with the quiet time level, at mid to low latitudes it does not increase (at fixed altitudes) above the quiet reference level. Meanwhile, the ionospheric storm is positive there. We conclude that the positive phase of the ionospheric storm is mainly due to uplifting of ionospheric F2-region plasma at mid latitudes and its equatorward movement at low latitudes along geomagnetic field lines caused by large-scale neutral wind circulation and the passage of travelling atmospheric disturbances (TADs). The calculated zonal electric field disturbances also help to create the positive ionospheric disturbances both at middle and low latitudes. Minor contributions arise from the general density enhancement of all constituents during geomagnetic storms, which favours ion production processes above ion losses at fixed height under day-light conditions.Key words: Atmospheric composition and structure (thermosphere · composition and chemistry) · Ionosphere (ionosphere · atmosphere interactions; modelling and forecasting)
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Kronberg, E. A., J. Woch, N. Krupp, and A. Lagg. "A summary of observational records on periodicities above the rotational period in the Jovian magnetosphere." Annales Geophysicae 27, no. 6 (June 25, 2009): 2565–73. http://dx.doi.org/10.5194/angeo-27-2565-2009.
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Abstract. The Jovian magnetosphere is a very dynamic system. The plasma mass-loading from the moon Io and the fast planetary rotation lead to regular release of mass from the Jovian magnetosphere and to a change of the magnetic topology. These regular variations, most commonly on several (2.5–4) days scale, were derived from various data sets obtained by different spacecraft missions and instruments ranging from auroral images to in situ measurements of magnetospheric particles. Specifically, ion measurements from the Galileo spacecraft represent the periodicities, very distinctively, namely the periodic thinning of the plasma sheet and subsequent dipolarization, and explosive mass release occurring mainly during the transition between these two phases. We present a review of these periodicities, particularly concentrating on those observed in energetic particle data. The most distinct periodicities are observed for ions of sulfur and oxygen. The periodic topological change of the Jovian magnetosphere, the associated mass-release process and auroral signatures can be interpreted as a global magnetospheric instability with analogies to the two step concept of terrestrial substorms. Different views on the triggering mechanism of this magnetospheric instability are discussed.
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Palmroth, Minna, Maxime Grandin, Theodoros Sarris, Eelco Doornbos, Stelios Tourgaidis, Anita Aikio, Stephan Buchert, et al. "Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models." Annales Geophysicae 39, no. 1 (February 25, 2021): 189–237. http://dx.doi.org/10.5194/angeo-39-189-2021.
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Abstract. The lower-thermosphere–ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200 km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI.
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Stellmacher, M., K. H. Glassmeier, R. L. Lysak, and M. G. Kivelson. "Field line resonances in discretized magnetospheric models: an artifact study." Annales Geophysicae 15, no. 6 (June 30, 1997): 614–24. http://dx.doi.org/10.1007/s00585-997-0614-0.
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Abstract. For more than two decades numerical models of the Earth's magnetosphere have been used successfully to study magnetospheric dynamic features such as the excitation of ULF pulsations and the mechanism of field line resonance. However, numerical formulations simplify important properties of the real system. For instance the Alfvén continuum becomes discrete because of a finite grid size. This discretization can be a possible source of numerical artefacts. Therefore a careful interpretation of any observed features is required. Examples of such artefacts are presented using results from a three dimensional dipole model of the magnetosphere, including an inhomogeneous distribution of the Alfvén velocity.
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Uritsky, V. M., and M. I. Pudovkin. "Low frequency 1/<i>f</i>-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere." Annales Geophysicae 16, no. 12 (December 31, 1998): 1580–88. http://dx.doi.org/10.1007/s00585-998-1580-x.
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Abstract. Low frequency stochastic variations of the geomagnetic AE-index characterized by 1/f b-like power spectrum (where f is a frequency) are studied. Based on the analysis of experimental data we show that the Bz-component of IMF, velocity of solar wind plasma, and the coupling function of Akasofu are insufficient factors to explain these behaviors of the AE-index together with the 1/f b fluctuations of geomagnetic intensity. The effect of self-organized criticality (SOC) is proposed as an internal mechanism to generate 1/f b fluctuations in the magnetosphere. It is suggested that localized spatially current instabilities, developing in the magnetospheric tail at the initial substorm phase can be considered as SOC avalanches or dynamic clusters, superposition of which leads to the 1/f b fluctuations of macroscopic characteristics in the system. Using the sandpile model of SOC, we undertake numerical modeling of space-localized and global disturbances of magnetospheric current layer. Qualitative conformity between the disturbed dynamics of self-organized critical state of the model and the main phases of real magnetospheric substorm development is demonstrated. It is also shown that power spectrum of sandpile model fluctuations controlled by real solar wind parameters reproduces all distinctive spectral features of the AE fluctuations.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind · magnetosphere interactions; storms and substroms).
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Moiseev, Aleksey, Sergei Starodubtsev, and Vladimir Mishin. "FEATURES OF EXCITATION AND AZIMUTHAL AND MERIDIONAL PROPAGATION OF LONG-PERIOD Pi3 OSCILLATIONS OF THE GEOMAGNETIC FIELD ON DECEMBER 8, 2017." Solar-Terrestrial Physics 6, no. 3 (September 22, 2020): 46–59. http://dx.doi.org/10.12737/stp-63202007.
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We study the Pi3 pulsations (with a period T=15–30 min) that were recorded on December 8, 2017 at ground stations in the midnight sector of the magnetosphere at the latitude range of DP2 current system convective electrojets. We have found that Pi3 are especially pronounced in the pre-midnight sector with amplitude of up to 300 nT and duration of up to 2.5 hrs. The pulsation amplitude rapidly decreased with decreasing latitude from F′=72° to F′=63°. The event was recorded during the steady magnetospheric convection. In the southward Bz component of the interplanetary magnetic field, irregular oscillations were detected in the Pi3 frequency range. They correspond to slow magnetosonic waves occurring without noticeable variations in the dynamic pressure Pd. Ground-based geomagnetic observations have shown azimuthal propagation of pulsations with a 0.6–10.6 km/s velocity east and west of the midnight meridian. An analysis of the dynamics of pulsations along the meridian has revealed their propagation to the equator at a velocity 0.75–7.87 km/s. In the projection onto the magnetosphere, the velocities are close in magnitude to the observed propagation velocities of substorm injected electrons. In the dawn-side magnetosphere during ground-observed Pi3 pulsations, compression mode oscillations were recorded.
We conclude that propagation of geomagnetic field oscillations in this event depends on the dynamics of particle injections under the action of a large-scale electric field of magnetospheric convection, which causes the plasma to move to Earth due to reconnection in the magnetotail. Small-scale oscillations in the magnetosphere were secondary, excited by the solar wind oscillations penetrating into the magnetosphere.
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Moiseev, Aleksey, Sergei Starodubtsev, and Vladimir Mishin. "FEATURES OF EXCITATION AND AZIMUTHAL AND MERIDIONAL PROPAGATION OF LONG-PERIOD Pi3 OSCILLATIONS OF THE GEOMAGNETIC FIELD ON DECEMBER 8, 2017." Solnechno-Zemnaya Fizika 6, no. 3 (September 22, 2020): 56–72. http://dx.doi.org/10.12737/szf-63202007.
Full textAbstract:
We study the Pi3 pulsations (with a period T=15–30 min) that were recorded on December 8, 2017 at ground stations in the midnight sector of the magnetosphere at the latitude range of DP2 current system convective electrojets. We have found that Pi3 are especially pronounced in the pre-midnight sector with amplitude of up to 300 nT and duration of up to 2.5 hrs. The pulsation amplitude rapidly decreased with decreasing latitude from F′=72° to F′=63°. The event was recorded during the steady magnetospheric convection. In the southward Bz component of the interplanetary magnetic field, irregular oscillations were detected in the Pi3 frequency range. They correspond to slow magnetosonic waves occurring without noticeable variations in the dynamic pressure Pd. Ground-based geomagnetic observations have shown azimuthal propagation of pulsations with a 0.6–10.6 km/s velocity east and west of the midnight meridian. An analysis of the dynamics of pulsations along the meridian has revealed their propagation to the equator at a velocity 0.75–7.87 km/s. In the projection onto the magnetosphere, the velocities are close in magnitude to the observed propagation velocities of substorm injected electrons. In the dawn-side magnetosphere during ground-observed Pi3 pulsations, compression mode oscillations were recorded.
We conclude that propagation of geomagnetic field oscillations in this event depends on the dynamics of particle injections under the action of a large-scale electric field of magnetospheric convection, which causes the plasma to move to Earth due to reconnection in the magnetotail. Small-scale oscillations in the magnetosphere were secondary, excited by the solar wind oscillations penetrating into the magnetosphere.
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Korth, H., B. J. Anderson, and C. L. Waters. "Statistical analysis of the dependence of large-scale Birkeland currents on solar wind parameters." Annales Geophysicae 28, no. 2 (February 10, 2010): 515–30. http://dx.doi.org/10.5194/angeo-28-515-2010.
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Abstract. The spatial distributions of large-scale field-aligned Birkeland currents have been derived using magnetic field data obtained from the Iridium constellation of satellites from February 1999 to December 2007. From this database, we selected intervals that had at least 45% overlap in the large-scale currents between successive hours. The consistency in the current distributions is taken to indicate stability of the large-scale magnetosphere–ionosphere system to within the spatial and temporal resolution of the Iridium observations. The resulting data set of about 1500 two-hour intervals (4% of the data) was sorted first by the interplanetary magnetic field (IMF) GSM clock angle (arctan(By/Bz)) since this governs the spatial morphology of the currents. The Birkeland current densities were then corrected for variations in EUV-produced ionospheric conductance by normalizing the current densities to those occurring for 0° dipole tilt. To determine the dependence of the currents on other solar wind variables for a given IMF clock angle, the data were then sorted sequentially by the following parameters: the solar wind electric field in the plane normal to the Earth–Sun line, Eyz; the solar wind ram pressure; and the solar wind Alfvén Mach number. The solar wind electric field is the dominant factor determining the Birkeland current intensities. The currents shift toward noon and expand equatorward with increasing solar wind electric field. The total current increases by 0.8 MA per mV m−1 increase in Eyz for southward IMF, while for northward IMF it is nearly independent of the electric field, increasing by only 0.1 MA per mV m−1 increase in Eyz. The dependence on solar wind pressure is comparatively modest. After correcting for the solar dynamo dependencies in intensity and distribution, the total current intensity increases with solar wind dynamic pressure by 0.4 MA/nPa for southward IMF. Normalizing the Birkeland current densities to both the median solar wind electric field and dynamic pressure effects, we find no significant dependence of the Birkeland currents on solar wind Alfvén Mach number.
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Mendillo, M., and C. Narvaez. "Ionospheric storms at geophysically-equivalent sites – Part 1: Storm-time patterns for sub-auroral ionospheres." Annales Geophysicae 27, no. 4 (April 7, 2009): 1679–94. http://dx.doi.org/10.5194/angeo-27-1679-2009.
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Abstract. The systematic study of ionospheric storms has been conducted primarily with groundbased data from the Northern Hemisphere. Significant progress has been made in defining typical morphology patterns at all latitudes; mechanisms have been identified and tested via modeling. At higher mid-latitudes (sites that are typically sub-auroral during non-storm conditions), the processes that change significantly during storms can be of comparable magnitudes, but with different time constants. These include ionospheric plasma dynamics from the penetration of magnetospheric electric fields, enhancements to thermospheric winds due to auroral and Joule heating inputs, disturbance dynamo electrodynamics driven by such winds, and thermospheric composition changes due to the changed circulation patterns. The ~12° tilt of the geomagnetic field axis causes significant longitude effects in all of these processes in the Northern Hemisphere. A complementary series of longitude effects would be expected to occur in the Southern Hemisphere. In this paper we begin a series of studies to investigate the longitudinal-hemispheric similarities and differences in the response of the ionosphere's peak electron density to geomagnetic storms. The ionosonde stations at Wallops Island (VA) and Hobart (Tasmania) have comparable geographic and geomagnetic latitudes for sub-auroral locations, are situated at longitudes close to that of the dipole tilt, and thus serve as our candidate station-pair choice for studies of ionospheric storms at geophysically-comparable locations. They have an excellent record of observations of the ionospheric penetration frequency (foF2) spanning several solar cycles, and thus are suitable for long-term studies. During solar cycle #20 (1964–1976), 206 geomagnetic storms occurred that had Ap≥30 or Kp≥5 for at least one day of the storm. Our analysis of average storm-time perturbations (percent deviations from the monthly means) showed a remarkable agreement at both sites under a variety of conditions. Yet, small differences do appear, and in systematic ways. We attempt to relate these to stresses imposed over a few days of a storm that mimic longer term morphology patterns occurring over seasonal and solar cycle time spans. Storm effects versus season point to possible mechanisms having hemispheric differences (as opposed to simply seasonal differences) in how solar wind energy is transmitted through the magnetosphere into the thermosphere-ionosphere system. Storm effects versus the strength of a geomagnetic storm may, similarly, be related to patterns seen during years of maximum versus minimum solar activity.
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Correia, Emilia, Luca Spogli, Lucilla Alfonsi, Claudio Cesaroni, Adriana M. Gulisano, Evan G. Thomas, Ray F. Hidalgo Ramirez, and Alexandre A. Rodel. "Ionospheric F-region response to the 26 September 2011 geomagnetic storm in the Antarctica American and Australian sectors." Annales Geophysicae 35, no. 5 (October 5, 2017): 1113–29. http://dx.doi.org/10.5194/angeo-35-1113-2017.
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Abstract. The ionospheric response at middle and high latitudes in the Antarctica American and Australian sectors to the 26–27 September 2011 moderately intense geomagnetic storm was investigated using instruments including an ionosonde, riometer, and GNSS receivers. The multi-instrument observations permitted us to characterize the ionospheric storm-enhanced density (SED) and tongues of ionization (TOIs) as a function of storm time and location, considering the effect of prompt penetration electric fields (PPEFs). During the main phase of the geomagnetic storm, dayside SEDs were observed at middle latitudes, and in the nightside only density depletions were observed from middle to high latitudes. Both the increase and decrease in ionospheric density at middle latitudes can be attributed to a combination of processes, including the PPEF effect just after the storm onset, dominated by disturbance dynamo processes during the evolution of the main phase. Two SEDs–TOIs were identified in the Southern Hemisphere, but only the first episode had a counterpart in the Northern Hemisphere. This difference can be explained by the interhemispheric asymmetry caused by the high-latitude coupling between solar wind and the magnetosphere, which drives the dawn-to-dusk component of the interplanetary magnetic field. The formation of polar TOI is a function of the SED plume location that might be near the dayside cusp from which it can enter the polar cap, which was the case in the Southern Hemisphere. Strong GNSS scintillations were observed at stations collocated with SED plumes at middle latitudes and cusp on the dayside and at polar cap TOIs on the nightside.
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Pokhotelov, D., I. J. Rae, K. R. Murphy, and I. R. Mann. "The influence of solar wind variability on magnetospheric ULF wave power." Annales Geophysicae 33, no. 6 (June 8, 2015): 697–701. http://dx.doi.org/10.5194/angeo-33-697-2015.
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Abstract. Magnetospheric ultra-low frequency (ULF) oscillations in the Pc 4–5 frequency range play an important role in the dynamics of Earth's radiation belts, both by enhancing the radial diffusion through incoherent interactions and through the coherent drift-resonant interactions with trapped radiation belt electrons. The statistical distributions of magnetospheric ULF wave power are known to be strongly dependent on solar wind parameters such as solar wind speed and interplanetary magnetic field (IMF) orientation. Statistical characterisation of ULF wave power in the magnetosphere traditionally relies on average solar wind–IMF conditions over a specific time period. In this brief report, we perform an alternative characterisation of the solar wind influence on magnetospheric ULF wave activity through the characterisation of the solar wind driver by its variability using the standard deviation of solar wind parameters rather than a simple time average. We present a statistical study of nearly one solar cycle (1996–2004) of geosynchronous observations of magnetic ULF wave power and find that there is significant variation in ULF wave powers as a function of the dynamic properties of the solar wind. In particular, we find that the variability in IMF vector, rather than variabilities in other parameters (solar wind density, bulk velocity and ion temperature), plays the strongest role in controlling geosynchronous ULF power. We conclude that, although time-averaged bulk properties of the solar wind are a key factor in driving ULF powers in the magnetosphere, the solar wind variability can be an important contributor as well. This highlights the potential importance of including solar wind variability especially in studies of ULF wave dynamics in order to assess the efficiency of solar wind–magnetosphere coupling.
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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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Stubbs, T. J., M. Lockwood, P. Cargill, M. Grande, B. Kellett, and C. Perry. "A comparison between ion characteristics observed by the POLAR and DMSP spacecraft in the high-latitude magnetosphere." Annales Geophysicae 22, no. 3 (March 19, 2004): 1033–46. http://dx.doi.org/10.5194/angeo-22-1033-2004.
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Abstract. We study here the injection and transport of ions in the convection-dominated region of the Earth's magnetosphere. The total ion counts from the CAMMICE MICS instrument aboard the POLAR spacecraft are used to generate occurrence probability distributions of magnetospheric ion populations. MICS ion spectra are characterised by both the peak in the differential energy flux, and the average energy of ions striking the detector. The former permits a comparison with the Stubbs et al. (2001) survey of He2+ ions of solar wind origin within the magnetosphere. The latter can address the occurrences of various classifications of precipitating particle fluxes observed in the topside ionosphere by DMSP satellites (Newell and Meng, 1992). The peak energy occurrences are consistent with our earlier work, including the dawn-dusk asymmetry with enhanced occurrences on the dawn flank at low energies, switching to the dusk flank at higher energies. The differences in the ion energies observed in these two studies can be explained by drift orbit effects and acceleration processes at the magnetopause, and in the tail current sheet. Near noon at average ion energies of ≈1keV, the cusp and open LLBL occur further poleward here than in the Newell and Meng survey, probably due to convection- related time-of-flight effects. An important new result is that the pre-noon bias previously observed in the LLBL is most likely due to the component of this population on closed field lines, formed largely by low energy ions drifting earthward from the tail. There is no evidence here of mass and momentum transfer from the solar wind to the LLBL by non-reconnection coupling. At higher energies ≈2–20keV), we observe ions mapping to the auroral oval and can distinguish between the boundary and central plasma sheets. We show that ions at these energies relate to a transition from dawnward to duskward dominated flow, this is evidence of how ion drift orbits in the tail influence the location and behaviour of the plasma populations in the magnetosphere. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions; magnetospheric configuration and dynamic)
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Watanabe, Masakazu, Takashi Tanaka, and Shigeru Fujita. "Magnetospheric Dynamo Driving Large‐scale Birkeland Currents." Journal of Geophysical Research: Space Physics 124, no. 6 (June 2019): 4249–65. http://dx.doi.org/10.1029/2018ja026025.
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Rème, H., C. Aoustin, J. M. Bosqued, I. Dandouras, B. Lavraud, J. A. Sauvaud, A. Barthe, et al. "First multispacecraft ion measurements in and near the Earth’s magnetosphere with the identical Cluster ion spectrometry (CIS) experiment." Annales Geophysicae 19, no. 10/12 (September 30, 2001): 1303–54. http://dx.doi.org/10.5194/angeo-19-1303-2001.
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Abstract. On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)
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Chernogor, L. F. "PHYSICAL EFFECTS OF THE POWERFUL TONGA VOLCANO EXPLOSION IN THE EARTH – ATMOSPHERE – IONOSPHERE – MAGNETOSPHERE SYSTEM ON JANUARY 15, 2022." Kosmìčna nauka ì tehnologìâ 29, no. 2 (April 28, 2023): 54–77. http://dx.doi.org/10.15407/knit2023.02.054.
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The Tonga volcano explosion has already been considered in many papers, which investigate the effects of tsunamis, explosiveatmospheric waves, traveling ionospheric disturbances, the perturbations of the equatorial anomaly, rearrangement of the ionospheric currents and of the atmospheric wind pattern, disturbances in the geomagnetic field, etc. It is reliably established that the explosion of the Tonga volcano caused a number of processes on a global scale. However, the mo deling of these processes is absent in the literature. The volcano is able to launch a whole complex of physical processes in all geophysical fields of the Earth (lithosphere, tectonosphere, ocean) – atmosphere – ionosphere – magnetosphere (EAIM) system. Analysis of the entire set of processes in the system caused by a unique explosion and volcanic eruption is a pressing scientific issue. The scientific objective of this study is to perform a comprehensive analysis and modeling of the main physical processes within the EAIM system, which accompanied the powerful explosion of the Tonga volcano on January 15, 2022. The article attempts to model or estimate the magnitude of the main effects caused by the explosion and eruption of the Tonga volcano. A comprehensive analysis and modeling of the main physical processes in the EAIM system, which accompanied the powerful explosi on and eruption of the Tonga volcano on January 15, 2022, has been performed. The energetics of the volcano and the explosive atmospheric wave has been estimated. The thermal energy of the volcano attained ~ 3.9×1018 J, while the mean thermal power has been estimated to be 9.1×1013 W. The energy of the explosive atmospheric wave was about 16–17 Mt TNT. The volcanic flow with an initial pressure of tens of atmospheres was determined to reach a few kilometers height, while the volcanic plume attained the peak altitude of 50–58 k m and moved 15 Mm we stward. The main parameters of the plume have been estimated. The plume’s mean power was 7.5 TW, and its heat flux was 15 MW/m2. With such a flux, one should have expected the appearance of a fire tornado with an ~0.17 s–1 angular frequency or a 37 s tornado rotation period. An analytical relation has been derived for estimating the maximum altitude of the plume rise. The main contribution to the magnitude of this altitude makes the volumetric discharge rate. The volcano explosion was accompanied by the generation of seismic and explosive atmospheric waves, tsunamis, Lamb waves, atmospheric gravity waves, infrasound, and sound, which propagated on a global scale. It is important to note that the powerful explosiveatmospheric wave could launch a secondary seismic wave and a secondary tsunami, which was one of the manifestations of subsystem couplings in the EAIM system. The propagation of powerful waves was accompanied by non-linear distortions of the wave profiles and non-linear attenuation as a result of the self-action of the waves. The electric processes in the troposphere are associated with spraying the eruption products, the electrification of the constituent particles in the plume, a charge separation, perturbations in the global electric circuit, and with an increase in the atmospheric electric field, the electric conductivity, and the electric current. The electric effect in the ionosphere is due to an increase in the strength of the ionospheric electric field by one or two orders of magnitude, which resulted in the secondary processes in the magnetosphere and the inner radiation belt. The magnetic effect of the submarine volcano explosion and eruption was established to be significant (~100–1,000 nT) but local. The magnetic effect in the ionosphere was due to the perturbations of the ionospheric dynamo current system under the action of the ionospheric hole (B ~ 0.1–1 nT) and due to the generation of the external current in the field of atmospheric waves (B ~ 1–10 nT). Dusting the atmosphere with the eruption plume led to the scattering of solar radiation by aerosols, the disturbance of the radiation balance in the Earth’s surface–ocean–atmosphere system, the cooling of the atmosphere at the airearth boundary, and the trigger effect. The volcano explosion caused the generation of aperiodic (ionospheric hole) and quasisinusoidal (wave) perturbations. Wave perturbations exhibited two characteristic speeds, ~300 m/s, which is close to the speed of the Lamb wave, and 700–1,000 m/s, which are typical for atmospheric gravity waves at ionospheric heights. The magnetospheric effects, first of all, are caused by powerful electromagnetic waves in the ~ 10–100 kHz range from tens to hundreds of thousands of lightning discharges that occurred in the volcanic plume. The energy and power of these radio emissions have been estimated to be 40–400 GJ and 40–400 GW, respectively. These emissions acted to cause precipitation of relativistic electrons from the radiation belt into the ionosphere and to enhance the ionization in the ~70–120 km altitude range. It is important to note that the burs t of precipitation was triggered. The Alfvén waves that propagated from their source along magnetic field lines had a certain effect on the magnetosphere. The direct and reverse, positive and negative couplings between the components of the EAIM system have been determined and validated.
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Zong, Qiugang. "Magnetospheric response to solar wind forcing: ultra-low-frequency wave–particle interaction perspective." Annales Geophysicae 40, no. 1 (February 28, 2022): 121–50. http://dx.doi.org/10.5194/angeo-40-121-2022.
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Abstract. Solar wind forcing, e.g., interplanetary shock and/or solar wind dynamic pressure pulses impacting Earth's magnetosphere, manifests many fundamental important space physics phenomena, including producing electromagnetic waves, plasma heating, and energetic particle acceleration. This paper summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma physics based on in situ spacecraft measurements, ground-based magnetometer data, magnetohydrodynamics (MHD) and kinetic simulations. Magnetosphere response to solar wind forcing is not just a “one-kick” scenario. It is found that after the impact of solar wind forcing on Earth's magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change in interplanetary shock or solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to generation of a series of waves, including poloidal-mode ultra-low-frequency (ULF) waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region response to the impact usually contains two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression, (2) followed by the wave–particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. Generalized theory of drift and drift–bounce resonance with growth- or decay-localized ULF waves has been developed to explain in situ spacecraft observations. The wave-related observational features like distorted energy spectrum, “boomerang” and “fishbone” pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the framework of this generalized theory. It is worth pointing out here that poloidal ULF waves are much more efficient at accelerating and modulating electrons (fundamental mode) in the radiation belt and charged ions (second harmonic) in the ring current region. The results presented in this paper can be widely used in solar wind interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune and other astrophysical objects with magnetic fields.
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Sandholt, P. E., C. J. Farrugia, and W. F. Denig. "Transitions between states of magnetotail–ionosphere coupling and the role of solar wind dynamic pressure: the 25 July 2004 interplanetary CME case." Annales Geophysicae 33, no. 4 (April 1, 2015): 427–36. http://dx.doi.org/10.5194/angeo-33-427-2015.
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Abstract. In a case study, we investigate transitions between fundamental magnetosphere–ionosphere (M-I) coupling modes during storm-time conditions (SYM-H between −100 and −160 nT) driven by an interplanetary coronal mass ejection (ICME). We combine observations from the near tail, at geostationary altitude (GOES-10), and electrojet activities across the auroral oval at postnoon-to-dusk and midnight. After an interval of strong westward electrojet (WEJ) activity, a 3 h long state of attenuated/quenched WEJ activity was initiated by abrupt drops in the solar wind density and dynamic pressure. The attenuated substorm activity consisted of brief phases of magnetic field perturbation and electron flux decrease at GOES-10 near midnight and moderately strong conjugate events of WEJ enhancements at the southern boundary of the oval, as well as a series of very strong eastward electrojet (EEJ) events at dusk, during a phase of enhanced ring current evolution, i.e., enhanced SYM-H deflection within −120 to −150 nT. Each of these M-I coupling events was preceded by poleward boundary intensifications and auroral streamers at higher oval latitudes. We identify this mode of attenuated substorm activity as being due to a magnetotail state characterized by bursty reconnection and bursty bulk flows/dipolarization fronts (multiple current wedgelets) with associated injection dynamo in the near tail, in their braking phase. The latter process is associated with activations of the Bostrøm type II (meridional) current system. A transition to the next state of M-I coupling, when a full substorm expansion took place, was triggered by an abrupt increase of the ICME dynamic pressure from 1 to 5 nPa. The brief field deflection events at GOES-10 were then replaced by a 20 min long interval of extreme field stretching (Bz approaching 5 nT and Bx ≈ 100 nT) followed by a major dipolarization (Δ Bz ≈ 100 nT). In the ionosphere the latter stage appeared as a "full-size" stepwise poleward expansion of the WEJ. It thus appears that the ICME passage led to fundamentally different M-I coupling states corresponding to different levels of dynamic pressure (Pdyn) under otherwise very similar ICME conditions. Full WEJ activity, covering a wide latitude range across the auroral oval in the midnight sector, was attenuated by the abrupt dynamic pressure decrease and resumed after the subsequent abrupt increase.
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Burne, Sofía, César Bertucci, Nick Sergis, Laura F. Morales, Nicholas Achilleos, Beatriz Sánchez-Cano, Yaireska Collado-Vega, Sergio Dasso, Niklas J. T. Edberg, and Bill S. Kurth. "Space Weather in the Saturn–Titan System." Astrophysical Journal 948, no. 1 (May 1, 2023): 37. http://dx.doi.org/10.3847/1538-4357/acc738.
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Abstract New evidence based on Cassini magnetic field and plasma data has revealed that the discovery of Titan outside Saturn’s magnetosphere during the T96 flyby on 2013 December 1 was the result of the impact of two consecutive interplanetary coronal mass ejections (ICMEs) that left the Sun in 2013 early November and interacted with the moon and the planet. We study the dynamic evolution of Saturn's magnetopause and bow shock, which evidences a magnetospheric compression from late November 28 to December 4 (at least), under prevailing solar wind dynamic pressures of 0.16–0.3 nPa. During this interval, transient disturbances associated with the two ICMEs are observed, allowing for the identification of their magnetic structures. By analyzing the magnetic field direction, and the pressure balance in Titan’s induced magnetosphere, we show that Cassini finds Saturn’s moon embedded in the second ICME after being swept by its interplanetary shock and amid a shower of solar energetic particles that may have caused dramatic changes in the moon’s lower ionosphere. Analyzing a list of Saturn's bow shock crossings during 2004–2016, we find that the magnetospheric compression needed for Titan to be in the supersonic solar wind can be generally associated with the presence of an ICME or a corotating interaction region. This leads to the conclusion that Titan would rarely face the pristine solar wind, but would rather interact with transient solar structures under extreme space weather conditions.
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Sandholt, P. E., Y. Andalsvik, and C. J. Farrugia. "Polar cap convection/precipitation states during Earth passage of two ICMEs at solar minimum." Annales Geophysicae 28, no. 4 (April 30, 2010): 1023–42. http://dx.doi.org/10.5194/angeo-28-1023-2010.
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Abstract. We report important new aspects of polar cap convection and precipitation (dawn-dusk and inter-hemisphere asymmetries) associated with the different levels of forcing of the magnetosphere by two interplanetary (IP) magnetic clouds on 20 November 2007 and 17 December 2008 during solar minimum. Focus is placed on two intervals of southward magnetic cloud field with large negative By components (Bx=−5 versus 0 nT) and with high and low plasma densities, respectively, as detected by spacecraft Wind. The convection/precipitation states are documented by DMSP spacecraft (Southern Hemisphere) and SuperDARN radars (Northern Hemisphere). The (negative) By component of the cloud field is accompanied by a newly-discovered flow channel (called here FC 2) threaded by old open field lines (in polar rain precipitation) at the dusk and dawn sides of the polar cap in the Northern and Southern Hemispheres, respectively, and a corresponding Svalgaard-Mansurov (S-M) effect in ground magnetic deflections. On 20 November 2007 the latter S-M effect in the Northern winter Hemisphere appears in the form of a sequence of six 5–10 min long magnetic deflection events in the 71–74° MLAT/14:30–16:00 MLT sector. The X-deflections are consistent with the flow direction in FC 2 (i.e. caused by Hall currents) in both IP cloud cases. The presence of a lobe cell and associated polar arcs in the Southern (summer) Hemisphere in the low density (1–2 cm−3) and Bx=0 ICME case is accompanied by the dropout of polar rain precipitation in the dusk-side regime of sunward polar cap convection and inward-directed Birkeland current. The low-altitude observations are discussed in terms of momentum transfer via dynamo processes in the high- and low-latitude boundary layers and Birkeland currents located poleward of the traditional R1-R2 system.
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Volwerk, M., J. Berchem, Y. V. Bogdanova, O. D. Constantinescu, M. W. Dunlop, J. P. Eastwood, P. Escoubet, et al. "Interplanetary magnetic field rotations followed from L1 to the ground: the response of the Earth's magnetosphere as seen by multi-spacecraft and ground-based observations." Annales Geophysicae 29, no. 9 (September 8, 2011): 1549–69. http://dx.doi.org/10.5194/angeo-29-1549-2011.
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Abstract. A study of the interaction of solar wind magnetic field rotations with the Earth's magnetosphere is performed. For this event there is, for the first time, a full coverage over the dayside magnetosphere with multiple (multi)spacecraft missions from dawn to dusk, combined with ground magnetometers, radar and an auroral camera, this gives a unique coverage of the response of the Earth's magnetosphere. After a long period of southward IMF Bz and high dynamic pressure of the solar wind, the Earth's magnetosphere is eroded and compressed and reacts quickly to the turning of the magnetic field. We use data from the solar wind monitors ACE and Wind and from magnetospheric missions Cluster, THEMIS, DoubleStar and Geotail to investigate the behaviour of the magnetic rotations as they move through the bow shock and magnetosheath. The response of the magnetosphere is investigated through ground magnetometers and auroral keograms. It is found that the solar wind magnetic field drapes over the magnetopause, while still co-moving with the plasma flow at the flanks. The magnetopause reacts quickly to IMF Bz changes, setting up field aligned currents, poleward moving aurorae and strong ionospheric convection. Timing of the structures between the solar wind, magnetosheath and the ground shows that the advection time of the structures, using the solar wind velocity, correlates well with the timing differences between the spacecraft. The reaction time of the magnetopause and the ionospheric current systems to changes in the magnetosheath Bz seem to be almost immediate, allowing for the advection of the structure measured by the spacecraft closest to the magnetopause.
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Hudson, M. K., R. E. Denton, M. R. Lessard, E. G. Miftakhova, and R. R. Anderson. "A study of Pc-5 ULF oscillations." Annales Geophysicae 22, no. 1 (January 1, 2004): 289–302. http://dx.doi.org/10.5194/angeo-22-289-2004.
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Abstract. A study of Pc-5 magnetic pulsations using data from the Combined Release and Radiation Effects Satellite (CRRES) was carried out. Three-component dynamic magnetic field spectrograms have been used to survey ULF pulsation activity for the approximate fourteen month lifetime of CRRES. Two-hour panels of dynamic spectra were examined to find events which fall into two basic categories: 1) toroidal modes (fundamental and harmonic resonances) and 2) poloidal modes, which include compressional oscillations. The occurence rates were determined as a function of L value and local time. The main result is a comparable probability of occurence of toroidal mode oscillations on the dawn and dusk sides of the magnetosphere inside geosynchronous orbit, while poloidal mode oscillations occur predominantly along the dusk side, consistent with high azimuthal mode number excitation by ring current ions. Pc-5 pulsations following Storm Sudden Commencements (SSCs) were examined separately. The spatial distribution of modes for the SSC events was consistent with the statistical study for the lifetime of CRRES. The toroidal fundamental (and harmonic) resonances are the dominant mode seen on the dawn-side of the magnetosphere following SSCs. Power is mixed in all three components. In the 21 dusk side SSC events there were only a few examples of purely compressional (two) or radial (one) power in the CRRES study, a few more examples of purely toroidal modes (six), with all three components predominant in about half (ten) of the events. Key words. Magnetospheric physics (MHD waves and instabilities; magnetospheric configuration and dynamics) – Space plasma physics (waves and instabilities)