• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.62.1-62.1
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• 2017

In space weather forecast, it is important to determine three-dimensional properties of CMEs. Using 29 limb CMEs, we examine which cone type is close to a CME three-dimensional structure. We find that most CMEs have near full ice-cream cone structure which is a symmetrical circular cone combined with a hemisphere. We develop a full ice-cream cone model based on a new methodology that the full ice-cream cone consists of many flat cones with different heights and angular widths. By applying this model to 12 SOHO/LASCO halo CMEs, we find that 3D parameters from our method are similar to those from other stereoscopic methods (i.e., a triangulation method and a Graduated Cylindrical Shell model). In addition, we derive CME mean density (${\bar{\rho}_{CME}}={\frac{M_{total}}{V_{cone}}}$) based on the full ice-cream cone structure. For several limb events, we determine CME mass by applying the Solarsoft procedure (e.g., cme_mass.pro) to SOHO/LASCO C3 images. CME volumes are estimated from the full ice-cream cone structure. For the first time, we derive average CME densities as a function of CME height for several CMEs, which are well fitted to power-law functions. We will compare densities (front and average) of geoeffective CMEs and their corresponding ICME ones.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.61.4-62
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• 2017

In this study we have made a statistical investigation on the kinematic classification of coronal mass ejections (CMEs) using about 4,000 SOHO/LASCO CMEs from 1996 to 2015. For this we use their SOHO/LASCO C3 data and exclude all poor events. Using the constant acceleration model, we classify these CMEs into three groups: Acceleration group, Constant Velocity group, and Deceleration group. For classification we adopt four different methods: Acceleration method, Velocity Variation method, Height Contribution method, and Visual Inspection method. Our major results are as follows. First, the fractions of three groups depend on the method used. Second, the results of the Height Contribution method are most consistent with those of the Visual Inspection method, which is thought to be most promising. Third, the fractions of different kinematic groups for the Height contribution method are: Acceleration (35%), Constant speed (47%), and Deceleration (18%). Fourth, the fraction strongly depend on CME speed; the fraction of Acceleration decreases from 0.6 to 0.05 with CME speed; the fraction of Constant increases from 0.3 to 0.7; the fraction of Deceleration increases from 0.1 to 0.3. Finally we present dozens of CMEs with non-constant accelerations. It is found that about 40 % of these CMEs show quasi-periodic oscillations.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.50.2-50.2
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• 2019

Understanding three-dimensional structure and parameters (e.g., radial velocity, angular width, source location and density) of coronal mass ejections (CMEs) is essential for space weather forecast. In this study, we determine CME mean density in solar corona and near the Earth. We select 38 halo CMEs, which have the corresponding interplanetary CMEs (ICMEs), by SOHO/LASCO from 2000 to 2014. To estimate a CME volume, we assume that a CME structure is a full ice-cream cone which is a symmetrical circular cone combined with a hemisphere. We derive CME mean density as a function of radial height, which are approximately fitted to power-law functions. The average of power-law indexes is about 2.1 in the LASCO C3 field of view. We also obtain power-law functions for both CME mean density at 21 solar radii and ICME mean density at 1AU, with the average power-law index of 2.6. We estimate a ratio of CME density to background density based on the Leblanc et al.(1998) at 21 solar radii. Interestingly, the average of the ratios is 4.0, which is the same as a default value used in the WSA-ENLIL model.

• Journal of The Korean Astronomical Society
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• v.55 no.3
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• pp.67-74
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• 2022

In this study, we perform a statistical investigation of the kinematic classification of 4,264 coronal mass ejections (CMEs) from 1996 to 2015 observed by SOHO/LASCO C3. Using the constant acceleration model, we classify these CMEs into three groups: deceleration, constant velocity, and acceleration motion. For this, we devise three different classification methods using fractional speed variation, height contribution, and visual inspection. The main results of this study can be summarized as follows. First, the fractions of three groups depend on the method used. Second, about half of the events belong to the groups of acceleration and deceleration. Third, the fractions of three motion groups as a function of CME speed are consistent with one another. Fourth, the fraction of acceleration motion decreases as CME speed increases, while the fractions of other motions increase with speed. In addition, the acceleration motions are dominant in low speed CMEs whereas the constant velocity motions are dominant in high speed CMEs.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2021.11a
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• pp.195-197
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• 2021

한국의 현대 해운업이 불과 반세기 만에 세계적인 수준으로 성장하는 데 해기사가 주도적인 역할을 했음은 주지의 사실이다. 이는 1960년대 중반에 시작된 해외취업과 외화획득, 선원송출업, 해운대리점업, 선박소유 등의 연관 산업의 발전을 통해 해운산업의 성장에 '내부 '파급효과'와 '외부경제 효과'를 미쳤기 때문이다. 그 중에서도 해외취업선원의 외화획득은 경제발전 초창기에 절대적으로 필요했던 외화를 제공했다는 점에서 그 경제적 의의가 컸다고 할 수 있다. 1965년부터 1999년까지 해외취업 선원들은 82억 6178달러를 벌어들인 데 반해, 파독 근로자들은 1963년부터 1977년까지 1억 15만달러를 국내로 송금한 데 그쳤다. 이 연구에서는 1978년에서 1992년까지 미국선사인 Lasco에 취업했던 해기사의 월급여명세서를 분석해 해기사의 평생 임금수입액을 계산해 볼 것이다. 분석 결과, 11년 5개월간 승선기간 동안 24만 3230달러(1억 6606만 7839원)을 벌어들인 것으로 나타났다. 이는 승선기간 월평균 120만 5282원의 수입을 올린 것으로 우리나라 제조업 월평균임금의 약 3.8배에 상당하는 것이고, 1963-1977년까지 파독근로자 1인의 평균외화송금액 5273달러에 비해 46배에 상응하는 것이다.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.72.2-72.2
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• 2014

We have made a comparison of three cone models (an asymmetric cone model, an ice-cream cone model, and an elliptical cone model) in terms of space weather application. We found that CME angular widths obtained by three cone models are quite different one another even though their radial velocities are comparable with one another. In this study, we investigate which cone model is proper for halo CME morphology and whether cone model parameters are similar to observations. For this, we look for CMEs which are identified as halo CMEs by one spacecraft and as limb CMEs by the other ones. For this we use SOHO/LASCO and STEREO/SECCHI data during the period from 2010 December to 2011 June when two spacecraft were separated by $90{\pm}10$ degrees. From geometrical parameters of these CMEs such as their front curvature, we classify them into two groups: shallow cone (5 events) and near full-cone (28 events). Noting that the previous cone models are based on flat cone or shallow cone shapes, our results imply that a cone model based on full cone shape should be developed. For further analysis, we are estimating the angular widths of these CMEs near the limb to compare them with those from the cone models. This result shows that the angular widths of the ice-cream cone model are well correlated (CC = 0.81) with those of observations.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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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.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.37.1-37.1
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• 2009

Solar type II radio burst is regarded as a signature of coronal shock. However its association with coronal mass ejections (CMEs)-driven shock and/or flare blast waves remains controversial. On December 31 2007, SOHO/LASCO and STEREO/COR observed a CME that occurred on the east limb of the Sun. Meanwhile, two type II bursts were observed sequently by KASI/E-Callisto and the Culgoora radio observatory during the CME apparence time. In this study, we estimate kinematics of the two coronal shocks from dynamic spectrum of the multiple type II bursts and compare with the kinematics of the CME derived from the space observations. An origin of the multiple type II bursts is inspected and discussed briefly.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.76.2-76.2
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• 2014

코로나그래프는 우주환경의 변화의 주요원인인 코로나물질방출을 관측할 수 있는 핵심우주관측기이다. 지난 약 18여년간 운용되어 왔던 SOHO 위성의 LASCO (Large Angle and Spectrometric Coronagraph) 탑재체의 노후화로 인한 운용 종료를 앞두고 있어 새로운 코로나그래프의 개발이 시급하다. 본 연구에서는 우주환경예보의 활용과 태양코로나와 코로나물질 방출에 관한 새로운 과학적 발견을 위해 적합한 위성용 코로나그래프의 개발방향을 제안하고 국제우주정거장이나 우리나라 위성을 활용하여 개발하는 경우에 극복해야 할 현실적인 기술 한계와 극복 방안에 대해 토의한다.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.49.3-49.3
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• 2019

햇무리(halo) 모양 코로나질량방출(coroanl mass ejection) 현상은 1970년대 후반 처음 발견된 이후, 그 물리적 본질에 대해 많은 논쟁이 있었다. 우주 망원경 SOHO LASCO의 고분해능 관측이후, 햇무리 모양은 시선방향에 나란한 방향으로 팽창하며 진행하는 고깔모양의 자기 구조(cone-shaped magnetic flux rope)가 2차원 관측이미지에 투영된 것으로 해석하는 것이 정설이다. 우리는 이러한 해석이 사실인지 관측을 이용해 검증하고, 타당한 물리적 해석을 찾는다. 이를 위해 STEREO 우주선이 SOHO에서 관측한 태양의 측면을 관측했던 2010년부터 2012년 관측자료를 사용하고, SOHO에서 관측한 햇무리 모양의 코로나질량방출 현상의 측면 모습이 예전의 해석대로 고깔모양을 보여주는지 STEREO 우주선의 관측자료와 비교한다. 우리는 햇무리 모양이 시선방향에 상관없는 이 현상 고유의 모양임을 확인 했으며 극자외선 관측결과와 수치계산 결과와 비교하여 이 햇무리 모양은 파동 현상의 결과임을 알았다. 이는 코로나질량방출 현상과 관련한 해석에 많은 변화가 필요함을 의미한다.