Kyung-Suk Cho

The Eruption from a Sigmoidal Solar Active Region on 2005 May 13

This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar NOAA AR 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at the TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption, as evidenced by the multiwavelength data ranging from Hα, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether cutting to allow the flux rope to rise upward, or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Hα data show that the first scenario is relevant to this eruption. As in other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. The radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXRs. Finally, type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001.

Magnetic Field Strength in the Solar Corona from Type II Band Splitting

The phenomenon of band splitting in type II bursts can be a unique diagnostic for the magnetic field in the corona, which is, however, inevitably sensitive to the ambient density. We apply this diagnostic to the CME-flare event on 2004 August 18, for which we are able to locate the propagation of the type II burst and determine the ambient coronal electron density by other means. We measure the width of the band splitting on a dynamic spectrum of the bursts observed with the Green Bank Solar Radio Burst Spectrometer (GBSRBS), and convert it to the Alfven Mach number under the Rankine-Hugoniot relation. We then determine the Alfven speed and magnetic field strength using the coronal background density and shock speed measured with the MLSO/MK4 coronameter. In this way we find that the shock compression ratio is in the range of 1.5-1.6, the Alfvenic Mach number is 1.4-1.5, the Alfven speed is 550-400 km s-1, and finally the magnetic field strength decreases from 1.3 to 0.4 G while the shock passes from 1.6 to 2.1 R☉. The magnetic field strength derived from the type II spectrum is finally compared with the potential field source surface (PFSS) model for further evaluation of this diagnostic.

A study of CME and type II shock kinematics based on coronal density measurement

Aims. The aim of this paper is to determine location and speed of a coronal shock from a typexa0II burst spectrum without relying on any coronal density model, and to use the result to discuss the relationship between the typexa0II burst and Coronal Mass Ejection (CME). Methods. This study is made for the 2004 August 18 solar eruption observed by Green Bank Solar Radio Burst Spectrometer (GBSRBS) and a limb CME/streamer simultaneously detected by Mauna Loa Solar Observatory (MLSO) MK4 coronameter. We determine the background density distribution over the area of interest by inverting the MLSO MK4 polarization map taken just before the CMExa0onset. Using the two-dimensional density distribution and the typexa0II emission frequencies, we calculate the typexa0II shock heights along several radial directions selected to encompass the entire position angles of the CME. We then compare these emission heights with those of the CMExa0to determine at which position angle the typexa0II burst propagated. Along the most plausible position angle, we finally determine the height and speed of the shock as functions of time. Results. It turns out that the typexa0II emission height calculated along a southern streamer best agrees to the observed height of the CMExa0flank. Along this region, both the shock and CMExa0moved at a speed ranging fromxa0800 toxa0600xa0kmu2009

DEVELOPMENT OF DATA INTEGRATION SYSTEM FOR GROUND-BASED SPACE WEATHER OBSERVATIONAL FACILITIES

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Development of the camera lens system for total solar eclipse observation (Conference Presentation)

. We also found that the streamer boundary already had enhanced density compared to other parts before the CME and formed a low Alfvenic region. Conclusions. We therefore conclude that the typexa0II burst was generated at the interface of the CMExa0flank and the streamer, as favorable for the shock formation.

Formation of a large-scale quasi-circular flare ribbon enclosing three-ribbon through two-step eruptive flares

Korea Astronomy and Space Science Institute, Daejeon 305-348, KoreaE-mail: jhbaek@kasi.re.kr(Received September 06, 2013; Accepted September 27, 2013)ABSTRACT We have developed a data integration system for ground-based space weather facilities in Korea Astronomy and Space Science Institute (KASI). The data integration system is necessary to analyze and use ground-based space weather data efficiently, and consists of a server system and data monitoring systems. The server system consists of servers such as data acquisition server or web server, and storage. The data monitoring systems include data collecting and processing applications and data display monitors. With the data integration system we operate the Space Weather Monitoring Lab (SWML) where real-time space weather data are displayed and our ground-based observing facilities are monitored. We expect that this data integration system will be used for the highly efficient processing and analysis of the current and future space weather data at KASI.Key words: space weather; data integration system; ground-based observational system: solar telescope, magnetometer, VHF radar

Relation of CME Speed and Magnetic Helicity in the Source Region during Increasing Phase of Solar Cycle 24

Korea Astronomy and Space Science Institute (KASI) has been developing the Camera Lens System (CLS) for the Total Solar Eclipse (TSE) observation. In 2016 we have assembled a simple camera system including a camera lens, a polarizer, bandpass filters, and CCD to observe the solar corona during the Total Solar Eclipse in Indonesia. Even we could not obtain the satisfactory result in the observation due to poor environment, we obtained some lessons such as poor image quality due to ghost effect from the lens system. For 2017 TSE observation, we have studied and adapted the compact coronagraph design proposed by NASA. The compact coronagraph design dramatically reduces the volume and weight and can be used for TSE observation without an external occulter which blocks the solar disk. We are in developing another camera system using the compact coronagraph design to test and verify key components including bandpass filter, polarizer, and CCD, and it will be used for the Total Solar Eclipse (TSE) in 2017. We plan to adapt this design for a coronagraph mission in the future. In this report we introduce the progress and current status of the project and focus on optical engineering works including designing, analyzing, testing, and building for the TSE observation.