• 전기학회논문지
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• 제58권10호
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• pp.2005-2010
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• 2009

Water droplet ejection characteristics of a point-to-plate airgap, with a wet porous point as a corona electrode, has been investigated. And the water droplet traces, charge, mass and number were measured experimentally. More particles are observed with wet porous point than metal point because the corona-discharging wet porous point can eject a number of water droplets. The water droplets ejected from the positive-corona-discharging wet porous point showed very fine traces as compared with those from the negative-corona-discharging wet porous point. Moreover, the water droplets ejected from the AC-corona-discharging wet porous point showed granular-like larger traces. It was shown that the weak corona discharge can eject smaller water droplets with larger ratio of mass-to-charge than the intense corona discharge.

• 천문학회보
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• 제42권2호
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• pp.82.1-82.1
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• 2017

After a coronal mass ejection occur, plasma blobs are often observed along the post-CME ray. Searching for features related to the plasma blobs would be important in understanding their origin. We investigated the morphology of solar flares at EUV wavelengths, around the estimated times when blobs were formed. We focused on three events - 2013 September 21 and 22, 2015 March 7 and 8, and 2017 July 13 and 14 - observed by Atmospheric Imaging Assembly (AIA) aboard Solar Dynamic Observatory (SDO). Around the blob ejection times on 2013 September 21 and 22 and 2017 July 13 and14, we found regions with recurrent events of pronounced flux increase in EUV images. Around those of 2015 March 7 and 8, however, we could not observe such recurrent flux increase. This illustrates that even though blob ejections along different post-CME rays look similar in the high corona, the assocated features in the low corona may differ. We conclude that magnetic morphology and CME triggering process should be carefully examined in order to classify plasma blobs by their nature.

• 천문학회보
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• 제35권1호
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• pp.26.1-26.1
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• 2010

In this talk we outline the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration which generates high-energy particles. The key physical processes producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in a current sheet to cause shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes that affect lower atmosphere such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been develops, where numerical simulation is a strong tool in that it can reproduce the time-dependent, nonlinear evolution of a flare. In this talk we review various models of a flare proposed so far, explaining key features of individual models. We introduce the general properties of flares by referring observational results, then discuss the processes of energy build-up, release, and transport, all of which are responsible for a flare. We will come to a concluding viewpoint that flares are the manifestation of the recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which has been disrupted via interaction with convective plasma while rising through the convection zone.

• 한국위성정보통신학회논문지
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• 제6권2호
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• pp.102-106
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• 2011

태양폭발, 코로나물질방출(Corona Mass Ejection, CME)등의 태양활동을 포함한 우주환경(space environment)은 결코 인간에게 우호적이지만은 않다. 특히 인공위성에게는 치명적일 수 있다. 그 중에서 정지궤도에 있는 통신위성에게는 상기와 같은 급격한 태양활동뿐만 아니라 지속적으로 끊임없이 배출되는 전자, 양성자등 플라즈마 입자들로 인해 수명이 단축되고 있다. 통신위성을 구성하는 능동부품들은 플라즈마 입자들에 특히 약하기 때문이다. 이를 방지하기 위하여 방사능 차폐(Radiation Shielind)등을 하지만 이에 대한 비용이 매우 많이 드는 것이 사실이다. 그러므로 적절한 차폐가 필요하며 이를 위해서는 우주환경의 연구가 필요하다. 본 연구에서는 저궤도부터 우주탐사용 위성까지 모든 궤도영역의 인공위성의 이상현상등을 분석한 후 이것이 태양폭발, 지자기 폭풍등 우주환경이벤트와의 연관성을 조사해보고자 한다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.25.1-25.1
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• 2010

This talk outlines the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes related to a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in current sheets that causes shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes which affect lower atmospheres such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been developed, in which numerical simulation is a strong tool reproducing the time-dependent, nonlinear evolution of plasma before and after the onset of a flare. In this talk we review various models of a flare proposed so far, explaining key features of these models. We show observed properties of flares, and then discuss the processes of energy build-up, release, and transport, all of which are responsible for producing a flare. We come to a concluding view that flares are the manifestation of recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which was disrupted via interaction with convective plasma while it was rising through the convection zone.

• Journal of Astronomy and Space Sciences
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• 제26권4호
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• pp.479-486
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• 2009

태양 주기 23 기간 동안 발생한 태양 고에너지 양성자 이벤트(Solar Proton Events, SPE)와 그와 연관된 코로나 물질 방출(Corona Mass Ejection, CME) 사이의 상관관계를 통계적으로 살펴보았다. 1997-2006년 동안 일어난 63개의 SPE-CME 데이터 쌍을 조사해 본 결과, CME의 속도는 SPE의 상승 시간(rise time) 및 지속 시간(duration time) 등과 상관 계수가 높게 나타났다. 특별히 CME의 지구방향 인자(earthward direction parameter)는 SPE의 최대 플럭스와 높은 상관 계수를 보여 주었다. 기존의 태양 플레어 세기가 SPE의 세기에 미치는 영향은 CME의 지구방향 인자가 SPE의 플럭스의 세기에 미치는 영향과 그 상관계수가 유사하게 나타났다. 특히 SPE와 CME 지구 방향 인자와의 상관관계가 좋은 데이터들의 공통적인 특성은 모두 매우 빠른(>1400km/s) halo CME인 것으로 나타났다.

• 천문학회보
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• 제44권2호
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• pp.43.3-43.3
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• 2019

A coronal mass ejection (CME) mass is generally estimated by the total brightness measured from white-light coronagraph observations. The total brightness are determined from the integration of the Thomson scattering by free electrons of solar corona along the line of sight. It is difficult to estimate the masses of halo CMEs due to the projection effect. To solve this issue, we construct a synthetic halo CME with a power-law density distribution (ρ = ρ₀r^-3) based on a full ice-cream cone model using SOHO/LASCO C3 observations. Then we compute a conversion factor from observed CME mass to CME mass for each CME. The final CME mass is determined as their average value of several CME masses above 10 solar radii. Our preliminary analysis for six CMEs show that their CME mass are well determined within the mean absolute relative error in the range of 4 to 15 %.

• 천문학회보
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• 제37권2호
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• pp.111.1-111.1
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• 2012

We examine the relationship between a type II radio burst that started from an unusually high frequency of 425 MHz (fundamental component) and an associated white-light coronal mass ejection on 2011 February 13. The radio burst had a drift rate of 2.5 MHz/sec, indicating a relatively high shock speed. From SDO AIA observations we find that a loop-like erupting front sweeps across high density coronal loops near the start time of the burst (17:34:15 UT). We find fragmented structures of the type II burst, which indicates the signature of the shock propagating through the multiple loops. The deduced distance of shock formation (0.06 Rs) from flare center and speed of the shock (1100 km $s^{-1}$) using the measured density from AIA/SDO observations are comparable to the height (0.05 Rs, from the solar surface) and speed (700 km $s^{-1}$) of the CME leading edge observed by STEREO/EUVI. We conclude that the type II burst could be onset even in the low corona (41 Mm or 0.06 Rs, above the solar surface) if a fast CME shock passes through the high density loops.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.38.3-39
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• 2010

While major solar proton events (SPEs) come from the coronal mass eject (CME)-driven shocks in solar wind, there are many evidences that potentiality of CMEs to generate SPEs depends on its early evolution near the Sun and on different solar activities observed around the CME liftoff time. To decipher origin of SPE release, we have investigated onset time comparison of the SPE with CME, metric type II radio burst, and hard X-ray flare. For this, we select 30 SPEs observed from 1997 to 2006 by using the particle instrument ERNE onboard SOHO, which allows proton flux anisotropy measurement in the energy range ~10 - 50MeV. Onset time of the SPEs is inferred by considering the energy-dependent proton transport time. As results, we found that (1) SPE onset time is comparable to that of type II but later than type III onset time and HXR start time, (2) SPE onset time is mostly later than the peak time of HXR flare, (3) almost half of the SPE onsets occurred after the HXR emission, and (4) there are two groups of CME height at the onset time of SPE; one is the height below 5 Rs (low corona) and the other is above 5Rs (high corona). In this talk, we will present the onset time comparison and discuss about the origin of the SPE onset.

• 천문학회지
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• 제53권1호
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• pp.1-7
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• 2020

The recent study of Chae et al. (2017) found a one-to-one correspondence between plasma blobs outflowing along a ray formed after a coronal mass ejection (CME) and small X-ray flares. In the present work, we have examined the spatial configuration and the eruption process of the flares that are associated with the blobs by analyzing EUV images and magnetograms taken by the SDO/AIA and HMI. We found that the main flare and the successive small flares took place in a quadrupolar magnetic configuration characterized by predominant magnetic fields of positive polarity, two minor magnetic fragments of negative polarity, and a curved polarity inversion line between them, which suggests that the formation process of the blobs may be similar to that of the parent CME. We also found that the successive flares resulted in a gradual change of the quadrupolar magnetic configuration, and the relevant migration of flaring kernels. The three-dimensional geometry and the property of the current sheet, that is often supposed to be embedded in an observed post-CME ray, seem to keep changing because of mutual feedback between the successive flares and the temporal change of the magnetic field configuration. Our results suggest that the observed post-CME rays may not reflect the characteristics of the current sheet responsible for the impulsive phase of the flare.