• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.321-322
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• 1996

Using the data on the occurrences of the Ho: and soft X-ray flares for the time interval of January 1, 1986-May :31, 1994, we have studied the middle term(30-300days) pericities of the solar flare production during the activity cycle 22. Power analysis of the time seies of daily H$\alpha$ flare index in the northern hemisphere shows prominent periodicities at 220, 120, 109, and 92 days(see Figures l(a) and l(b)), while in the southern hemisphere, those at 267, 213, 183, 167, and 107 days are apparent, though their peaks are not so distint as those in the northern hemisphere. Periodogram of daily soft X-ray flare index also reveal the periodicities at 279, 205, 164, 117, and 91 days in the northern hemisphere, and at 266, 220, 199, 162, 120, and 100 days in the southern hemisphere. Howeer, the 155-day periodicity reported for the earlier cycles, 19, 20, and 21, could not be confirmed in our analysis. to be submitted to Solar Physics; an extended abstract.

• 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.38 no.2
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• pp.90.2-90.2
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• 2013

Filament eruptions are one of the energetic phenomena on the solar surface with flares and coronal mass ejections (CMEs). We observed the whole process of filament eruption that occurred in AR 11305 in association with a C5.6 flare on 2011 September 29th using the Fast Imaging Solar Spectrograph (FISS) and the Solar Dynamics Observatory (SDO). The eruption consists of a slow phase with a transverse speed of ~10 km $s^{-1}$ in 16 minutes and a fast phase with a transverse speed of ~200 km $s^{-1}$ in 3 minutes. Near the beginning of slow phase eruption, preflare brightening occurred beneath the filament in $H{\alpha}$ and some EUV images. The preflare brightening region is associated with a blue-shifted $H{\alpha}$ feature with a speed of ~60 km $s^{-1}$. It appears that this is the outflow from magnetic reconnection which may have occurred at relatively low atmosphere. Our result support the notion that the preflare brightening is a process of magnetic reconnection playing an important role in triggering the filament eruption by deformative the magnetic field lines under the eruptive filament.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.51.2-51.2
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• 2019

Multi-wavelength observations become very popular in astronomy. Even though there are some correlations among different sensor images, it is not easy to translate from one to the other one. In this study, we apply a deep learning method for image-to-image translation, based on conditional generative adversarial networks (cGANs), to solar images. To examine the validity of the method for scientific data, we consider several different types of pairs: (1) Generation of SDO/EUV images from SDO/HMI magnetograms, (2) Generation of backside magnetograms from STEREO/EUVI images, (3) Generation of EUV & X-ray images from Carrington sunspot drawing, and (4) Generation of solar magnetograms from Ca II images. It is very impressive that AI-generated ones are quite consistent with actual ones. In addition, we apply the convolution neural network to the forecast of solar flares and find that our method is better than the conventional method. Our study also shows that the forecast of solar proton flux profiles using Long and Short Term Memory method is better than the autoregressive method. We will discuss several applications of these methodologies for scientific research.

• Bulletin of the Korean Space Science Society
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• 1999.09a
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• pp.85-85
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• 1999

No Abstract, See Full Text

• Bulletin of the Korean Space Science Society
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• 2008.04a
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• pp.24.3-24.3
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• 2008

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.331-332
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• 1996

We present 3 rare subtypes of the FFSs observed with high temporal resolution at 4-frequency (1.42, 2.13, 2.84 and 4.2G GHz). The various FFSs occurred during the main and post-flare phase can demonstrate that coronal nonthermal electron acceleration/injection may go through the whole development process of flares, and deduce that there may exist the re-forming of loop-like structures in the post-flare phase, and the complex multi-type magnetic structures in corona.

• The Bulletin of The Korean Astronomical Society
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• v.33 no.2
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• pp.36.1-36.1
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• 2008

• Journal of Navigation and Port Research
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• v.35 no.9
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• pp.701-706
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• 2011

Radio waves including GPS signals, various TV communications, and radio broadcasting can be disturbed by a strong solar storm, which may occur due to solar flares and produce an ionospheric delay anomaly in the ionosphere according to the change of total electron content. Electron density irregularities can cause deep signal fading, frequently known as ionospheric scintillation, which can result in the positioning error using GPS signal. This paper proposes a detection algorithm for the ionosphere delay anomaly during a solar storm by using multi-reference stations. Different TEC grid which has irregular electron density was applied above one reference station. Then the ionospheric delay in zenith direction applied different TEC will show comparatively large ionospheric zenith delay due to the electron irregularity. The ionospheric slant delay applied an elevation angle at reference station was analyzed to detect the ionospheric delay anomaly that can result in positioning error. A simulation test was implemented and a proposed detection algorithm using data logged by four reference stations was applied to detect the ionospheric delay anomaly compared to a criterion.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.110.1-110.1
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• 2012

We studied the source regions of 12 solar energetic particle (SEP) events seen between 2010 August and 2012 January at STEREO-A, B and ACE, when the two STEREO spacecraft were separated by about $180^{\circ}$. All events were associated with strong flares (C1 - X6) and fast coronal mass ejections (CMEs) accompanied by type II radio bursts. We have determined the arrival times of the SEP events at the three spacecraft. EUV waves observed in $195{\AA}$ and $193{\AA}$ channels of STEREO and SDO/AIA are tracked across the Sun and the arrival time of the EUV wave at the photospheric source of open field lines extending to the spacecraft connection points at 2.5 Rsun estimated. We found 7 events with flux enhancements in all spacecraft and 4 in two spacecraft. Most events came from a single source. The results show that magnetic field connections between source regions and the spacecraft play an important role in abrupt flux enhancements. In the most cases, EUV waves at the Sun are associated with a wide longitudinal spread of the SEPs.