• 천문학회보
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• 제32권1호
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• pp.35.1-35.1
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• 2007

• 천문학회보
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• 제38권1호
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• pp.61.2-61.2
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• 2013

We study chromospheric oscillations including umbral flashes and running penumbral waves in a sunspot using scanning spectroscopy in H-alpha and Ca II 8542A, with the Fast Imaging Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. A bisector method is applied to spectral observations to construct chromospheric Doppler velocity maps. Temporal sequence analysis of these shows enhanced high-frequency oscillations inside the sunspot umbra in both lines. Their peak frequency gradually decreases outward from the umbra. The oscillation power is found to be associated with magnetic-field strength and inclination, with different relationships in different frequency bands.

• 천문학회보
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• 제39권1호
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• pp.71.1-71.1
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• 2014

To investigate physical properties of Solar pores, we use SDO/HMI data from 2010 to 2013. For this, we select single and isolated pores from the active region (Axx, Bxo, Bxi and Bxc-type) listed in Solar Region Summary. Pore is defined by connected pixels satisfying the intensity threshold from pixel of minimum intensity. We try to obtain area, intensity, magnetic field, and Doppler velocity of pores from HMI data. After removing the effects of orbital motion of the SDO satellite and differential rotation of the Sun, we identify that significant daily variations of Doppler velocity with non-zero ordinates still remain in the umbral region, and the artifact is quite dependent on the strength of magnetic field and radial component of velocity of SDO satellite. In this study we develope empirical model to remove the artifact. A preliminary result on the elimination of the artifact will be presented.

• 천문학회보
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• 제35권2호
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• pp.48.1-48.1
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• 2010

A numerical simulation study of the solar coronal plasma reveals that a ballooning instability can develop in the course of flux rope merging. When magnetic field lines from different flux ropes reconnect, a new field line connecting farther footpoints is generated. Since the field line length abruptly increases, the field line expands outward. If the plasma beta is low, this expansion takes place more or less evenly over the whole field line. If, on the other hand, the plasma beta is high enough somewhere in this field line, the outward expansion is not even, but is localized as in a bulging balloon. This ballooning section of the magnetic field penetrates out of the overlying field, and eventually the originally underlying field and the overlying field come to interchange their apex positions. This process may explain how a field structure that has stably been confined by an overlying field can occasionally show a localized eruptive behavior.

• Journal of Astronomy and Space Sciences
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• 제34권2호
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• pp.105-110
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• 2017

Solar wind density depletions are phenomena that solar wind density is rapidly decreased and keep the state. They are generally believed to be caused by the interplanetary (IP) shocks. However, there are other cases that are hardly associated with IP shocks. We set up a hypothesis for this phenomenon and analyze this study. We have collected the solar wind parameters such as density, speed and interplanetary magnetic field (IMF) data related to the solar wind density depletion events during the period from 1996 to 2013 that are obtained with the advanced composition explorer (ACE) and the Wind satellite. We also calculate two pressures (magnetic, dynamic) and analyze the relation with density depletion. As a result, we found total 53 events and the most these phenomena's sources caused by IP shock are interplanetary coronal mass ejection (ICME). We also found that solar wind density depletions are scarcely related with IP shock's parameters. The solar wind density is correlated with solar wind dynamic pressure within density depletion. However, the solar wind density has an little anti-correlation with IMF strength during all events of solar wind density depletion, regardless of the presence of IP shocks. Additionally, In 47 events of IP shocks, we find 6 events that show a feature of blast wave. The quantities of IP shocks are weaker than blast wave from the Sun, they are declined in a short time after increasing rapidly. We thus argue that IMF strength or dynamic pressure are an important factor in understanding the nature of solar wind density depletion. Since IMF strength and solar wind speed varies with solar cycle, we will also investigate the characteristics of solar wind density depletion events in different phases of solar cycle as an additional clue to their physical nature.

• 천문학회보
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• 제37권2호
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• pp.113.2-113.2
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• 2012

An innovative solar observing satellite, Hinode, has successfully observed the detailed evolution of a rapidly developing emerging flux region from the beginning of its appearance at the solar surface. The high spatial and temporal resolution provided by the satellite enables to capture the prominent dynamic processes such as the rotational motion of a polarity region with intense magnetic flux which is reminiscent of a cyclone on the Earth, and a running wave that spreads ahead of this rotating polarity region. This 'solar cyclone' is, on the other hand, generated differently from terrestrial cyclones, and a possible generating mechanism for it is demonstrated with a three-dimensional magnetohydrodynamic simulation of a twisted magnetic flux tube emerging from the solar interior into the solar atmosphere. The simulation shows that the rotational motion is caused by a strong downflow of plasma along the twisted field lines that form a helical pillar standing upright on the Sun.

• 천문학회지
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• 제9권1호
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• pp.1-6
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• 1976

The translational and reactive parts of thermal conductivity of a partially ionized solar magneto-plasma gas have been calculated based on Yun and Wyller's formulation (1972) along with Devoto's theory(1968). The computed results are presented as functions of temperature and pressure for given magnetic field strengths. The results of the calculations show that for most photospheric conditions the magnetic field does not play any important role in characterizing thermal properties of the ionized gas. However, when the gas pressure is low(e.g., P<10 dynes/$cm^2)$) the field becomes extremely effective even if its strength is quite small (e.g., B<0.1 gauss). The reactive part of the thermal transport is found to be very important when the gas is undertaking active ionization.

• 천문학회보
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• 제46권2호
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• pp.47.3-48
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• 2021

We studied the large scale dynamo process in a system forced by helical magnetic field. The dynamo process is basically nonlinear, but can be linearized with 𝛼&𝛽 coefficients and large scale magnetic field $\bar{B}$. This is very useful to the investigation of solar (stellar) dynamo. A coupled semi-analytic equations based on statistical mechanics are used to investigate the exact evolution of 𝛼&𝛽. This equation set needs only magnetic helicity ${\bar{H}}_M({\equiv}{\langle}{\bar{A}}{\cdot}{\bar{B}}{\rangle},\;{\bar{B}}={\nabla}{\times}{\bar{A}})$ and magnetic energy ${\bar{E}}_M({\equiv}{\langle}{\bar{B}}^2{\rangle}/2)$. They are fundamental physics quantities that can be obtained from the dynamo simulation or observation without any artificial modification or assumption. 𝛼 effect is thought to be related to magnetic field amplification. However, in reality the averaged 𝛼 effect decreases very quickly without a significant contribution to ${\bar{B}}$ field amplification. Conversely, 𝛽 effect contributing to the magnetic diffusion maintains a negative value, which plays a key role in the amplification with Laplacian ∇²(= - k²) for the large scale regime. In addition, negative magnetic diffusion accounts for the attenuation of plasma kinetic energy E_V(= 〈 U² 〉/2) (U: plasma velocity) when the system is saturated. The negative magnetic diffusion is from the interaction of advective term - U • ∇ B from magnetic induction equation and the helical velocity field. In more detail, when 'U' is divided into the poloidal component U_pol and toroidal one U_tor in the absence of reflection symmetry, they interact with - B • ∇ U and - U • ∇ B from ∇ × 〈 U × B 〉 leading to 𝛼 effect and (negative) 𝛽 effect, respectively. We discussed this process using the theoretical method and intuitive field structure model supported by the simulation result.

• 천문학논총
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• 제12권1호
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• pp.35-45
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• 1997

SOFT($\underline{So}lar\;\underline{F}lare\;\underline{T}elescope$) installed at BOAO(Bohyunsan Optical Astronomy Observatory) is purposed for observing solar active regions using four refractors on single mount with a $400"\times300"$ field of view: Two refractors with a diameter of 15cm(f15) are observe the white light and $H\alpha$, and the other two refractors with a diameter of 20cm(f8) are observe the magnetic field distribution and Doppler shifts at the solar chromosphere. Three Lyot filters, one of the most important observational instruments, are installed on the optical rails for VMG, LMG, and $H\alpha$ that possible to very narrow pass band observation under high precision stability of temperature. From the combination of KD*P and quarter wave plate in the Lyot filter possible observe the magnetic fields strength and doppler shifts by using the characteristics of polarization components. In this paper, we introduce the basic characteristics, optical system, and monitor system of the SOFT.

• 천문학회보
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• 제37권1호
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• pp.96.2-96.2
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• 2012

We statistically examined ULF Pc 3-5 wave power in the regions of undisturbed upstream solar wind, quasi-parallel shock (and foreshock), quasi-perpendicular shock, and the magnetosheath to understand how and to what extent the wave power changes as the solar wind propagates to the magnetosheath. For this study, we used the magnetic field data from the THEMIS spacecraft and Wind (as shifted to the bow shock nose) for May-November in 2008 and 2009. The statistical results show that, in the case of the Pc5 wave power, the sheath power is roughly proportional to the upstream power for both quasi-parallel (and foreshock) and quasi-perpendicular shock regions. Also we identified undisturbed upstream condition from WIND as being well away from foreshock region, and found that the sheath power can be larger for quasi-parallel shock region by a factor of 5-15 than for quasi-perpendicular shock region. In the cases of Pc 3 and Pc4 waves, we found the higher sheath power when associated with the foreshock than with the quasi-perpendicular shock region.