• 천문학회보
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• 제38권2호
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• pp.92.2-92.2
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• 2013

We revisit the 1.3-year (yr) signals observed on the Sun, in the interplanetary space, and in the Earth's magnetosphere to study the coupling among signals from the three regions for about forty years (1970--2007) covering three solar cycles 21, 22, and 23. For this, we make dynamic spectra of datasets including three different regions. From this, we estimate the peak frequency around 1.3 yr for each region and the corresponding band power. We found that coherent power only appears during 1987-1995 and the coherent behavior is found only in the interplanetary space and Earth, not in the Sun. Although the solar surface magnetic field shows significant power around 1.3 yr, their peak frequencies are statistically different from those of the outer regions, which make us to dismiss the existence of coherence among the three regions. But it is notable that the peaks in band power corresponding to the 1.3-yr period are clearly simultaneous in the interplanetary space and Earth.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2004년도 한국우주과학회보 제13권1호
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• pp.70-70
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• 2004

Lower thermospheric winds are forced primarily by non-uniform solar heating, atmospheric tides and other waves coming from below, and energy and momentum forcing associated with high-latitude magnetosphere-ionosphere coupling, particularly ion drag and Joule heating. To understand the physical processes that control the thermospheric dynamics, we quantify the momentum forces that are mainly responsible for maintaining the high-latitude lower thermospheric wind system and examine the resulting momentum balance with the aid of the Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM) developed by the National Center for Atmospheric Research. (omitted)

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2004년도 한국우주과학회보 제13권1호
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• pp.84-84
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• 2004

Using a one-dimensional MHD code of Total Variation Diminishing (TVD) scheme, we perform simulations of propagation of nonlinear magnetosonic waves. A magnetosonic wave is a longitudinal wave propagating perpendicularly to the magnetic field lines, and involves compression and rarefaction of the magnetic field lines and the plasma. We first confirm the theoretical solution of Lee and Kim (2000) for the evolution of nonlinear magnetosonic waves in the homogeneous space. (omitted)

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 1992년도 한국우주과학회보 제2권1호
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• pp.7.2-7
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• 1993

The interaction between the magnetic field and the accreting matter in the magnetic compact star has taken into account in order to find some constraints between physical paramerters in these systems. We show that the interaction radius, where the matter begins to funnel in the magnetosphere, can be described as a function of the magnetic moment acctetion rate and the width of the interaction zone. This radius, after estimated iteratively for a given parameter set has been used in order to study the radiation of X-rays in the magnetic compact star. Some results of such study in context with the interaction radius in the intermediate polar have been discussed.

• Journal of Astronomy and Space Sciences
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• 제16권2호
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• pp.293-306
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• 1999

태양 활동에 의해 방출된 고에너지 입자들은 위성 및 전기, 전파 통신 등의 기기의 작동에 여러 가지 영향을 끼치고 지구 자기권을 크게 섭동시킨다. 태양 활동의 영향에 따른 지구 근접 우주 환경의 변화를 이해하기 위해서는 지구 자기권과 전리층 및 대기에 관한 연구가 선행되어야 한다. 이러한 연구의 일환으로 지구의 자기장과 전리층 및 대기에 대한 여러 모델들을 제시하고 널리 사용되는 대표적인 모델들의 특징을 분석하였다. 본 연구에서는 국내 최초로 전리층 및 지자기 모델용 GUI 프로그램을 개발하였으며 특히 WEB 상에서 종합적인 자료 분석이 가능한 시스템을 개발하였다.

• 천문학회보
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• 제42권1호
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• pp.37.1-37.1
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• 2017

We consider a magnetic dipole model of a pulsar and investigate general relativistic effects on electromagnetic radiation from the pulsar. The general relativistic modifications should be found applicable to many well-known issues in pulsar astronomy. Among other things, the modifications of Goldreich-Julian model and subpulse drift would be of significant interest and challenging issues. The electromagnetic fields in the pulsar magnetosphere are computed by solving Maxwell's equations defined in the strongly curved spacetime around the pulsar, hence containing the properties of strong gravitational effects. On top of these effects, we also investigate the effects from rotation and obliqueness of the pulsar to work out the general relativistic versions of Goldreich-Julian model and subpulse drift.

• Journal of Astronomy and Space Sciences
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• 제17권2호
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• pp.233-240
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• 2000

Five scientific instruments are planned on KAISTSAT-4 that is scheduled to be launched in 2002. A far ultra-violet imaging spectrograph and a set of space plasma instruments are currently being designed. The imaging spectrograph will make observations of astronomical objects and Earth's upper atmosphere. The plasma instrumentation is capable of fast measuring the thermal magnetosphere plasmas, cold ionospheric plasmas and the Earth's magnetic fields. Major system drivers and constraints on the payloads as well as the spacecraft are identified. A preliminary analysis of the K-4 mission has been undertaken with the system requirements that are derived from the system drivers. Detailed investigation shows that Sun-synchronous orbits with approximate altitudes of 800km are optimal to satisfy the identified requirements. Comparisons with other orbits of different inclinations are also shown. Four operation modes and a daily schedule of spacecraft maneuver are found from the Sun-synchronous orbital model. It is shown that the scientific objectives of K-4 can be achieved with moderate levels of design and operation risks.

• 항공우주기술
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• 제3권1호
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• pp.86-96
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• 2004

우주 환경은 두꺼운 대기층에 의해 보호되는 지표 환경에서는 경험할 수 없는 여러 가지 위험 요소가 있다. 근 지구 궤도에서는 플라스마 대기 및 원자 산소 등에 의해 부식이 발생할 수 있으며, 강한 자외선과 입자 복사 등에 의해 위성을 구성하고 있는 재료나 전자 부품 등이 손상을 입을 수 있다. 따라서 위성의 설계 시에는 운용궤도에서 예상되는 환경요인을 적절히 예측하여 이에 대응하는 설계가 이루어지도록 해야 한다.

• 천문학회보
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• 제36권2호
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• pp.95.1-95.1
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• 2011

Halo Coronal Mass Ejections (HCMEs) are crucial for space weather, since they can produce severe geomagnetic storms when they interact with the Earth's magnetosphere. It is thus very important to infer their directions, radial velocities, and their three-dimensional structures. In this study, we apply two different models to HCMEs since 2008 : (1) an ice cream cone model by Xue et al (2005) using SOHO/LASCO data, (2) a flux rope model by Thernisien et al. (2009) using STEREO/SECCHI data. In addition, we use the flux rope model with zero separation angle of flux rope, which is morphologically similar to the ice cream cone model. The comparison shows that the CME radial velocities from three models have very good correlations (R>0.9) one another. We are extending this comparison to other partial halo CMEs observed by STEREO and SOHO.

• 천문학회지
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• 제23권1호
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• pp.63-70
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• 1990

The original axisymmetric, stationary electrodynamic model of the central engine in an active galactic nucleus proposed by Macdonald and Thorne consists of a supermassive black hole with magnetic field lines that pass through the region just outside the event horizon of the black hole. Each magnetic field line rotates with a constant angular velocity which will exceed the speed of light at large radii. Even though the field lines are purely mathematical entities this condition sets a stringent physical constraint on the motion of the magnetic field lines and the particles on them. In this paper we will show that we can remove this auxiliary constraint in our model by allowing nonstationary processes. As a result the magnetic field lines can be twisted and wound up in a region lying outside of the quasi-stationary magnetosphere of the black hole. We conclude that astrophysical jets are formed in that region due to the twisted and wound magnetic field lines powered by the Blandford-Znajek process and the other driving forces.