• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.50.4-50.4
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• 2019

We detect a new population of chromospheric jets in a polar coronal hole observed by Hinode/SOT. The propagating speed of the jets ranges in 30 - 490 km/s whose duration time is 3 - 52 s. The recurrent rate is approximately 3/min for a give segment of 1 arc-second horizontal interval. These jets are seemed to be more transient and faster than type II spicules at chromosphere, while the properties are compatible with the network jets seen in emission lines of transition region. We will discuss the implication of these jets for a coronal heating.

• Journal of Korean Neurosurgical Society
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• v.56 no.3
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• pp.243-247
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• 2014

Objective : To analyze the clinical data and surgical results from symptomatic chronic subdural hematoma (CSDH) patients who underwent burr-hole drainage (BHD) at the maximal thickness area and twist-drill craniostomy (TDC) at the precoronal point. Methods : We analyzed data from 65 symptomatic CSDH patients who underwent TDC at the pre-coronal point or BHD at the maximal thickness area. For TDC, we defined the pre-coronal point to be 1 cm anterior to the coronal suture at the level of the superior temporal line. TDC was performed in patients with CSDH that extended beyond the coronal suture, as confirmed by preoperative CT scans. Medical records, radiological findings, and clinical performance were reviewed and analyzed. Results : Of the 65 CSDH patients, 13/17 (76.4%) with BHD and 42/48 (87.5%) with TDC showed improved clinical performance and radiological findings after surgery. Catheter failure was seen in 1/48 (2.4%) cases of TDC. Five patients (29.4%) in the BHD group and four patients (8.33%) in the TDC group underwent reoperations due to remaining hematomas, and they improved with a second operation, BHD or TDC. Conclusion : Both BHD at the maximal thickness area and TDC at the pre-coronal point are safe and effective drainage methods for symptomatic CSDHs with reasonable indications.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.85.2-85.2
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• 2017

The coronal electron density is a fundamental and important physical quantity in solar physics for estimating coronal magnetic fields and analyzing solar radio bursts. To check a validation of coronal electron density distributions (CEDDs) from polarized brightness (pB) measurements with Van de Hulst inversions, we compare CEDDs derived from a polarized brightness (pB) observation [MLSO/MK4 coronameter] and one spectroscopic observation [SOHO/UVCS]. For this, we consider data observed in 2005 with the following conditions: (1) the observation time differences from each other are less than 1 minutes; and (2) O VI doublet (O VI $1031.9{\AA}$ and $1037.6{\AA}$) is well identified. In the pB observation, the CEDDs can be estimated by using Van de Hulst inversion methods. In the spectroscopic observation, we use the ratio of radiative and collisional components of the O VI doublet to estimate the CEDDs. We find that the CEDDs obtained from pB measurements are higher than those based on UVCS observations at the heights between 1.6 and 1.8 Rs (${\times}1.9$ for coronal streamer, 1.2 ~ 1.8 for background corona, and 1.5 for coronal hole), while they are lower than those based on UVCS at the heights between 1.9 and 2.6 Rs (${\times}0.1{\sim}0.6$ for coronal streamer, 0.5 ~ 0.7 for background corona, and 0.6 for coronal hole). The CEDDs of coronal streamers are higher than those of background corona at the between 1.6 and 2.0 Rs: ${\times}1.2{\sim}2.4$ for MK4 and 1.5 ~ 1.9 for UVCS.

• Journal of Astronomy and Space Sciences
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• v.33 no.3
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• pp.197-205
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• 2016

We investigated two flares in the solar atmosphere that occurred on June 3, 2012 and July 6, 2012 and caused propagation of Moreton and EIT waves. In the June 3 event, we noticed a filament winking which presumably was caused by the wave propagation from the flare. An interesting feature of this event is that there was a reflection of this wave by a coronal hole located alongside the wave propagation, but not all of this wave was transmitted by the coronal hole. Using the running difference method, we calculated the speed of Moreton and EIT waves and we found values of 926 km/s before the reflection and 276 km/s after the reflection (Moreton wave) and 1,127 km/s before the reflection and 46 km/s after the reflection (EIT wave). In the July 6 event, this phenomenon was accompanied by type II and type III solar radio bursts, and we also performed a running difference analysis to find the speed of the Moreton wave, obtaining a value of 988 km/s. The speed derived from the analysis of the solar radio burst was 1,200 km/s, and we assume that this difference was caused by the different nature of the motions in these phenomena, where the solar radio burst was caused by the propagating particles, not waves.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.1
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• pp.83.1-83.1
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.99-99
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• 2011

A statistical study of coronal hole merging and splitting has been performed through Solar Cycle 23. The NOAA/SESC solar synoptic maps are examined to identify inarguably clear events of coronal hole merging and splitting. The numbers of merging events and splitting events are more or less comparable regardless of the phase in the solar cycle. The number of both events, however, definitely shows the phase dependence in the solar cycle. It apparently has a minimum at the solar minimum whereas its maximum is located in the declining phase of the sunspot activity, about a year after the second peak in Solar Cycle 23. There are more events of merging and splitting in the descending phase than in the ascending phase. Interestingly, no event is found at the local minimum between the two peaks of the sunspot activity. This trend can be compared with the variation of the average magnetic field strength and the radial field component in the solar wind through the solar cycle. In Ulysses observations, both of these quantities have a minimum at the solar minimum while their maximum is located in the descending phase, a while after the second peak of the sunspot activity. At the local minimum between the two peaks in the solar cycle, the field strength and the radial component both have a shallow local minimum or an inflection point. At the moment, the physical reason for these resembling tendencies is difficult to understand with existing theories. Seeing that merging and splitting of coronal holes are possible by passage of opposite polarity magnetic structures, we may suggest that the energizing activities in the solar surface such as motions of flux tubes are not exactly in phase with sunspot generation, but are more active some time after the sunspot maximum.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.27.2-27.2
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• 2010

We have studied the formation of coronal holes (CHs) associated with halo CMEs. For this study, we used multi-wavelength data from Yohkoh Soft X-ray Telescope (SXT), GOES Soft X-ray Imager (SXI), SOHO EIT 195 ${\AA}$, SOHO MDI magnetogram, MLSO He I 10830 ${\AA}$, and BBSO H-alpha. The CHs are characterized by open magentic field regions with low emission, density, and temperature and their open fields drive high speed solar winds which cause geomagnetic storms. So far, the formation and the evolution of CHs are not well understood. The formation of the dark region associated with the eruption of a CME is well known as "coronal dimming" which may be caused by the mass depletion near the CME footpoint. It is different from a typical CH since it persists for only one or two days. In this study, we present three cases that show the formation of coronal holes which are associated with three halo CMEs: 1) 2000 Jul 14, 2) 2003 Oct 28, 3) 2005 May 13. In the first case, hot plasma was ejected during a weak eruption and then filled out the pre-existing CH. After the halo CME occurred, the hot plasma region becomes a CH again. In the second and the third cases, we found newly formed CHs just after their associated CMEs. All three coronal holes are associated with strong flares and persist over 3 days until they disappeared by the solar rotation. Examining the MDI magnetograms, we found that the magnetic polarity of each CH region has one polarity. Based on these results, we suggest that the coronal holes can be formed by the CMEs and they should be distinguished from the coronal dimming.

• Journal of Astronomy and Space Sciences
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• v.26 no.3
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• pp.305-316
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• 2009

In this study, we suggest an empirical forecast of CIR (Corotating Interaction Regions) and geomagnetic storm based on the information of coronal holes (CH). For this we used CH data obtained from He I $10830{\AA}$ maps at National Solar Observatory-Kitt Peak from January 1996 to November 2003 and the CIR and storm data that Choi et al. (2009) identified. Considering the relationship among coronal holes, CIRs, and geomagnetic storms (Choi et al. 2009), we propose the criteria for geoeffective coronal holes; the center of CH is located between $N40^{\circ}$ and $S40^{\circ}$ and between $E40^{\circ}$ and $W20^{\circ}$, and its area in percentage of solar hemispheric area is larger than the following areas: (1) case 1: 0.36%, (2) case 2: 0.66%, (3) case 3: 0.36% for 1996-2000, and 0.66% for 2001-2003. Then we present contingency tables between prediction and observation for three cases and their dependence on solar cycle phase. From the contingency tables, we determined several statistical parameters for forecast evaluation such as PODy (the probability of detection yes), FAR (the false alarm ratio), Bias (the ratio of "yes" predictions to "yes" observations) and CSI (critical success index). Considering the importance of PODy and CSI, we found that the best criterion is case 3; CH-CIR: PODy=0.77, FAR=0.66, Bias=2.28, CSI=0.30. CH-storm: PODy=0.81, FAR=0.84, Bias=5.00, CSI=0.16. It is also found that the parameters after the solar maximum are much better than those before the solar maximum. Our results show that the forecasting of CIR based on coronal hole information is meaningful but the forecast of goemagnetic storm is challenging.

• Bulletin of the Korean Space Science Society
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• 2009.04a
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• pp.46.2-46.2
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• 2009

• Journal of Korean Neurosurgical Society
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• v.52 no.2
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• pp.133-137
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• 2012

Objective : Twist-drill craniostomy (TDC) with closed-system drainage and burr-hole drainage (BHD) with a closed system are effective treatment options for chronic subdural hematoma (CSDH). The aim of this study was to analyze clinical data and surgical results from symptomatic CSDH patients who underwent TDC with closed-system drainage at the pre-coronal point (PCP). Methods : We analyzed data for 134 symptomatic CSDH patients who underwent TDC at the PCP with closed-system drainage. We defined the PCP for TDC to be 1 cm anterior to the coronal suture at the level of superior temporal line. TDC at the PCP with closed-system drainage was selected in patients with CSDH that extended beyond the coronal suture, confirmed by preoperative CT scans. Medical records, radiological findings, and clinical performance were reviewed retrospectively. Results : Of the 134 CSDH patients, 114 (85.1%) showed improved clinical performance and imaging findings after surgery. Catheter failures were seen in two cases (1.4%); the catheters were inserted in the epidural space. Recurrent cases were seen in eight patients (5.6%), and they were improved with a second BHD with a closed-system operation. Conclusion : TDC at the PCP with closed-system drainage is safe and effective for patients with symptomatic CSDH whose hematomas extend beyond the coronal suture.