• Title, Summary, Keyword: magnetosphere

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Evolution of the Magnetosphere in Response to a Sudden Ring Current Injection

  • Choe, G.S.;Park, Geun-Seok;Lee, Jung-Gi
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.100.2-100.2
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    • 2011
  • The dynamical evolution of the Earth's magnetosphere loaded with a transiently enhanced ring current is studied by numerical magnetohydrodynamic (MHD) simulation. Two cases with different values of the primitive ring current are considered. In one case, the initial ring current is strong enough to create a magnetic island in the magnetosphere. The magnetic island readily reconnects with the earth-connected ambient field and is destroyed as the system approaches a steady equilibrium. In the other case, the initial ring current is not so strong, and the initial magnetic field configuration bears no magnetic island, but a wake of bent field lines, which is smoothed out through the relaxing evolution of the magnetosphere. The relaxation time of the magnetosphere is found to be about five to six minutes, over which the ring current is reduced to about a quarter of its initial value. Before reaching a steady state, the magnetosphere is found to undergo an overshooting expansion and a subsequent contraction. Fast and slow magnetosonic waves are identified to play an important role in the relaxation toward equilibrium.

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PROPAGATION OF SUDDEN IMPULSES IN A DIPOLAR MAGNETOSPHERE

  • LEE DONG-HUN;SUNG SUK-KYUNG
    • Journal of The Korean Astronomical Society
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    • v.36 no.spc1
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    • pp.101-107
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    • 2003
  • The magnetosphere is often perturbed by impulsive input such as interplanetary shocks and solar wind discontinuities. We study how these initial perturbations are propagating within the magnetosphere over various latitude regions by adopting a three-dimensional numerical dipole model. We examine the wave propagation on a meridional plane in a time-dependent manner and compare the numerical results with multi-satellite and ground observations. The dipole model is used to represent the plasmasphere and magnetosphere with a realistic Alfven speed profile. It is found that the effects of refraction, which result from magnetic field curvature and inhomogeneous Alfven speed, are' found to become important near the plasmapause. Our results show that, when the disturbances are assumed at the subsolar point of the dayside magnetosphere, the travel time becomes smaller to the polar ionosphere compared to the equatorial ionosphere.

Magnetopause Waves Controlling the Dynamics of Earth's Magnetosphere

  • Hwang, Kyoung-Joo
    • Journal of Astronomy and Space Sciences
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    • v.32 no.1
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    • pp.1-11
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    • 2015
  • Earth's magnetopause separating the fast and often turbulent magnetosheath and the relatively stagnant magnetosphere provides various forms of free energy that generate low-frequency surface waves. The source mechanism of this energy includes current-driven kinetic physical processes such as magnetic reconnection on the dayside magnetopause and flux transfer events drifting along the magnetopause, and velocity shear-driven (Kelvin-Helmholtz instability) or density/pressure gradient-driven (Rayleigh-Taylor instability) magnetohydro-dynamics (MHD) instabilities. The solar wind external perturbations (impulsive transient pressure pulses or quasi-periodic dynamic pressure variations) act as seed fluctuations for the magnetopause waves and trigger ULF pulsations inside the magnetosphere via global modes or mode conversion at the magnetopause. The magnetopause waves thus play an important role in the solar wind-magnetosphere coupling, which is the key to space weather. This paper presents recent findings regarding the generation of surface waves (e.g., Kelvin-Helmholtz waves) at the Earth's magnetopause and analytic and observational studies accountable for the linking of the magnetopause waves and inner magnetospheric ULF pulsations, and the impacts of magnetopause waves on the dynamics of the magnetopause and on the inner magnetosphere.

THEMIS Pi2 observations near dawn and dusk sectors in the inner magnetosphere

  • Kwon, Hyuck-Jin;Kim, Khan-Hyuk;Lee, Dong-Hun;Takahashi, K.;Park, Young-Deuk;Bonnell, J.W.
    • Bulletin of the Korean Space Science Society
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    • pp.40.3-40.3
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    • 2010
  • The most frequently suggested source for Pi2 pulsations in the inner magnetosphere (L < 4) is standing fast-mode waves trapped in the plasmasphere (i.e., plasmaspheric resonances). They have been considered as the source of low-latitude Pi2 pulsations. The plasmaspheric resonance model suggests that compressional fast-mode waves can be detected at all local times inside the plasmasphere provided reflection of the wave energy is efficient. Until now, however, there are no reports about compressional Pi2s observed in the dayside inner magnetosphere. That is, there is longitudinal limit of inner magnetosphere. In February 2008, THEMIS probes were near dawn and/or dusk sides, which are the transition regions between the nightside and dayside, in the inner magnetosphere (L = 2-4) when low-altitude Pi2s were identified at Bohyun (L = 1.35) station in Korea. Using the THEMIS electric field data, we examined if Pi2s are excited by longitudinally localized disturbances. We found that compressional Pi2s having high coherence with a low-latitude Pi2 pulsation occur on dawnside. However, any compressional pulsations in the Pi2 frequency band were not detected on duskside. This indicates that compressional Pi2s disappear near the duskside. Our observations are discussed with spatial plasmaspheric structure and possible Pi2 mechanisms.

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The Development of the Black Hole Magnetosphere Model in the Last Thirty Years (블랙홀 자기권 모델 30년)

  • PARK SEOK JAE
    • Publications of The Korean Astronomical Society
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    • v.15 no.1
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    • pp.1-13
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    • 2000
  • Since Goldreich and Julian's pioneering work in 1969, the pulsar magnetosphere theory has been dramatically developed for theorists to possess an elegant axisymmetric, stationary model. Based on this development the black hole magnetosphere theory has also been established in the last 30 years. Such theoretical developments will be reviewd equation by equation in this paper.

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Global MHD Simulation of the Earth's Magnetosphere Event on October, 1999

  • PARK KYUNG SUN;OGINO TATSUKI
    • Journal of The Korean Astronomical Society
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    • v.34 no.4
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    • pp.317-319
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    • 2001
  • The response of the earth's magnetosphere to the variation of the solar wind parameters and Interplanetary magnetic field (IMF) has been stud}ed by using a high-resolution, three-dimension magnetohydrodynamic (MHD) simulation when the WIND data of velocity Vx, plasma density, dynamic pressure, By and Bz every 1 minute were used as input. Large electrojet and magnetic storm which occurred on October 21 and 22 are reproduced in the simulation (fig. 1). We have studied the energy transfer and tail reconnect ion in association with geomagnetic storms.

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LINE EMISSION FROM THE MAGNETOSPHERE OF MAGNETIC CATACLYSMIC VARIABLES (MCV 자기구에서의 선방출)

  • KIM YONGGI
    • Publications of The Korean Astronomical Society
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    • v.15 no.spc1
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    • pp.113-118
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    • 2000
  • A magnetic cataclysmic variable has a rotating magnetic white dwarf which accretes matter from its late type companion. Kim & Beuermann (1995) presented a phenomenological model of the accretion from its surrounding structure e.g., a disk into the magnetosphere of the white dwarf, and presented results for the spin modulated X-ray spectrum and light curves. Using this model, we calculate the optical continuum and line emission which result from reprocessing of X-rays in the accretion stream within the magnetosphere. Penning (1985) suggested the observed spin-modulated radial-velocity variations might result from reprocession of X-rays in the disk. We, however, find the radiation can be originated from the magnetosphere accretion stream. We use the same geometrical model to calculate the optical and the X-ray behaviour. The results from the two wavelength bands are internally consistent. We conclude that this approach will increase the diagnostic accuracies of the results.

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Simulation Study of Solar Wind Interaction with Lunar Magnetic Fields

  • Choi, Cheong Rim;Dokgo, Kyunghwan;Woo, Chang Ho;Min, Kyoung Wook
    • Journal of Astronomy and Space Sciences
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    • v.37 no.1
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    • pp.35-42
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    • 2020
  • Particle-in-cell simulations were performed to understand the interaction of the solar wind with localized magnetic fields on the sunlit surface of the Moon. The results indicated a mini-magnetosphere was formed which had a thin magnetopause with the thickness of the electron skin depth. It was also found that the solar wind penetrated into the cavity of the magnetosphere intermittently rather than in a steady manner. The solar wind that moved around the magnetosphere was observed to hit the surface of the Moon, implying that it may be the cause of the lunar swirl formation on the surface.

THE GRAD-SHAFRANOV EQUATION IN THE MACDONALD-THORNE MAGNETOSPHERE (MACDONALD-THORNE 자기권의 GRAD-SHAFRANOV 방정식)

  • PARK SEOK JAE
    • Publications of The Korean Astronomical Society
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    • v.14 no.2
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    • pp.57-60
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    • 1999
  • We derive the Grad-Shafranov equation in the Macdonald-Thorne magnetosphere of the super-massive black hole in an active galactic nucleus. Our major assumption is that the plasma velocity is not only toroidal but also poloidal. As a result, we get the correction terms which are related to the poloidal motion of plasma like electrodynamic jets.

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