• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.39.1-39.1
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• 2011

Coronal mass ejection (CME) plasmas have been observed in EUV and X-ray passbands as well as in white light. Mass of CME has been determined using polarized brightness observed by the Large Angle and Spectrometric Coronagraph Experiment (LASCO) on board Solar and Heliospheric Observatory (SOHO). Therefore, this mass obtained from the LASCO observation indicates the total CME mass. However, the mass of CME plasma in different temperatures can be determined in EUV and X-ray passbands using observations by SOHO/EIT, STEREO/EUVI, and Hinode/XRT. Prominence/CME plasmas have been observed as absorption or emission features in EUV and X-ray passbands. The absorption features provide a lower limit to cold mass. In addition, the emission features provide an upper limit to the mass of plasmas in temperature ranges of EUV and X-ray. We determine the mass constraints using the emission measure obtained by assuming the prominence/CME structures. This work will address the mass constraints of hot and cold plasmas in CMEs, comparing to total CME mass.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.85.1-85.1
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• 2015

We investigate the mass and energy of erupting plasma observed in X-rays and EUV, which is associated with a coronal mass ejection (CME) and an X-class flare. The erupting plasma was observed by both the X-ray telescope (XRT) on Hinode and the Atmospheric Imaging Assembly (AIA) on Solar Dynamic Observatory (SDO). We estimate the emission measures of the erupting plasma using a differential emission measure method. The plasma erupts with a loop-like structure in X-ray and EUV. We estimate the mass of erupting plasma assuming a cylinder structure. In addition, we estimate the radiative loss, thermal conduction, thermal, and kinetic energies of the eruptive hot plasma. We find that the thermal conduction timescale is much shorter than the duration of the eruption. This result implies that additional heating during the eruption may be required to explain the hot plasma observations in X-rays.

• Journal of The Korean Astronomical Society
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• v.56 no.1
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• pp.117-124
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• 2023

A Forbush decrease (FD) is a depression of cosmic ray (CR) intensity observed by ground-based neutron monitors (NMs). The CR intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection (ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of the NM station. However, sometimes NMs of almost the same cutoff rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on CR intensity modulation of FD event recorded at different NMs due to different ICME propagation directions as an additional parameter in the model explaining the CR modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We suggest the hypothesis that the asymmetric CR modulations of FD events are determined by the propagation directions of the associated ICMEs.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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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.

• Journal of The Korean Astronomical Society
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• v.42 no.6
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• pp.175-184
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• 2009

A method of estimating the lower bound of coronal magnetic field strength in the neighborhood of an ejecting plasmoid is presented. Based on the assumption that the plasma ejecta is within a magnetic island, an analytical expression for the force acting on the ejecta is derived. The method is applied to a limb coronal mass ejection event, and a lower bound of the magnetic field strength just below the CME core is estimated. The method is expected to provide useful information on the strength of reconnecting magnetic field if applied to X-ray plasma ejecta.

• The Bulletin of The Korean Astronomical Society
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• v.32 no.2
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• pp.68.1-68.1
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.32 no.1
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• pp.34.1-34.1
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.65.2-65.2
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• 2015

We developed a three-dimensional magnetohydrodynamic (MHD) code to reproduce the structure of a solar wind, the properties of a coronal mass ejection (CME) and the interaction between them. This MHD code is based on the finite volume method incorporating total variation diminishing (TVD) scheme with an unstructured grid system. In particular, this grid system can avoid the singularity at the north and south poles and relax tight CFL conditions around the poles, both of which would arise in a spherical coordinate system (Tanaka 1994). In this model, we first apply an MHD tomographic method (Hayashi et al. 2003) to interplanetary scintillation (IPS) observational data and derive a solar wind from the physical values obtained at 50 solar radii away from the Sun. By comparing the properties of this solar wind to observational data obtained near the Earth orbit, we confirmed that our model captures the velocity, temperature and density profiles of a solar wind near the Earth orbit. We then insert a spheromak-type CME (Kataoka et al. 2009) into the solar wind to reproduce an actual CME event. This has been done by introducing a time-dependent boundary condition to the inner boundary of our simulation domain. On the basis of a comparison between a simulated CME and observations near the Earth, we discuss the physics involved in an ICME interacting with a solar wind.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.97.1-97.1
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• 2014

We clarify the dynamics connecting a solar flare and a coronal mass ejection (CME) based on the results of a magnetohydrodynamic (MHD) simulation starting from a nonlinear force-free field (NLFFF) in Inoue et al. 2014. In previous studies, many authors proposed numerous candidates for triggering processes of a solar flare and the associated CME. Among them, the tether-cutting reconnection or the torus instability has been supported by recent simulations and observations. On the other hand, our MHD simulation in accordance with more realistic situations show that highly twisted field lines are first produced through a tether-cutting reconnection between the twisted field lines in the NLFFF, and then the newly formed, strongly twisted field erupts away from the solar surface because of a loss of equilibrium. This dynamics corresponds to the onset of a solar flare. Furthermore we have found that the strongly twisted erupting field reconnect with the weakly twisted ambient field during the eruption, creating a large flux tube, and then it rises over a critical height of the torus instability to trigger a CME. From these results, we conclude that the coupled process of tether-cutting reconnection and torus instability is important in the flare-CME relationship.

• Journal of The Korean Astronomical Society
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• v.35 no.3
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• pp.151-157
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• 2002

From the data of solar wind observation by ACE spacecraft orbiting the Earth-Sun Lagrangian point, we selected 48 forward interplanetary shocks(IPSs) occurred in 2000, maximum solar activity period. Examining the profiles of solar wind parameters, the IPSs are classified by their shock drivers. The significant shock drivers are the interplanetary coronal mass ejection(ICME) and the high speed stream(HSS). The IPSs driven by the ICMEs are classified into shocks driven by magnetic clouds and by ejectas based on the existence of magnetic flux rope structure and magnetic field strength. Some IPSs could be formed as the blast wave by the smaller energy and shorter duration of shock drivers such as type II radio burst. Out of selected 48 forward IPSs, $56.2\%$ of the IPSs are driven by ICME, $16.7\%$ by HSS, and $16.7\%$ of the shocks are classified into blast-wave type shocks. However, the shock drivers of remaining $10\%$ of the IPSs are unidentified. The classification of the IPSs by their driver is a first step toward investigating the critical magnitudes of the IPS drivers commencing the magnetic storms in each class.