• Title, Summary, Keyword: sun: active regions

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A METHOD FOR DETERMINING MAGNETIC HELICITY OF SOLAR ACTIVE REGIONS FROM SOHO/MDI MAGNETO GRAMS

  • CHAE JONGCHUL;JEONG HYEWON
    • Journal of The Korean Astronomical Society
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    • v.38 no.2
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    • pp.295-298
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    • 2005
  • Recently a big progress has been made on the measurements of magnetic helicity of solar active regions based on photospheric magnetograms . In this paper, we present the details of Chae's method of determining the rate of helicity transfer using line-of-sight magnetograms such as taken by SORO /MDI. The method is specifically applied to full-disk magnetograms that are routinely taken at 96-minute cadence.

SPECTROSCOPIC OBSERVATION OF THE SOLAR ACTIVE REGIONS IN HeI 10830 ${\AA}$ LINE

  • TOHMURA ICHIROH;KITAI REIZABURO;SUEMATSU YOSHINORI;SOLTAU DIRK
    • Journal of The Korean Astronomical Society
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    • v.29 no.spc1
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    • pp.333-335
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    • 1996
  • Here we report the results from spectroscopic observations of soloar active regions in the HeI 10830 ${\AA}$ line at the German Vacuum Tower Telescope(VTT) in Tenerife during the August 199:3 International EFR(Emerging Flux Region) Campaign. Four active regions in various stages of their evolution, i.e., NOAA7558, 7560, 7561, and 7562, were ovserved on 10 August 1993. From the observed HeI 10830 ${\AA}$ spectra in these active regions, spectroscopic quantities such as equivalent width(EW), doppler shift, doppler width, etc., were derived(see Figure l(a)) and the correlation between them were studied(see Figure l(b)). Our main results are as follows: (I)In NOAA7562, which is a young and evolving EFR, the EW is large, while it is small around a simple and roundish spot of NOAA7558. (2)In these active regions, redshift in the 10830 line is dominant when the EW is larger. (3)As the doppler width increases, the line tends to shift redward. (4)When the EW is smaller, it seems to exist another component which have dynamic characteristics different from the redshifting component. In NOAA7560 and NOAA7561, regions which have several small spots, the values of the EW are intermediate. Results (2) and (3) may suggest the possible existence of downflow above active regions, if the HeI 10830 ${\AA}$line is formed in the upper chromopshere, and it is consistent with the earlyer result from the SMM extreme-ultraviolet observation by Klimchuk(1987, Astrophys. J., 323, 368) (to be submitted. to Astronomy and Astrophysics; an extended abstract)

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MERGING AND FRAGMENTATION IN THE SOLAR ACTIVE REGION 10930 CAUSED BY AN EMERGING MAGNETIC FLUX TUBE WITH ASYMMETRIC FIELD-LINE TWIST DISTRIBUTION ALONG ITS AXIS

  • Magara, Tetsuya
    • Journal of The Korean Astronomical Society
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    • v.52 no.4
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    • pp.89-97
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    • 2019
  • We demonstrate the subsurface origin of the observed evolution of the solar active region 10930 (AR10930) associated with merging and breakup of magnetic polarity regions at the solar surface. We performed a magnetohydrodynamic simulation of an emerging magnetic flux tube whose field-line twist is asymmetrically distributed along its axis, which is a key to merging and fragmentation in this active region. While emerging into the surface, the flux tube is subjected to partial splitting of its weakly twisted portion, forming separate polarity regions at the solar surface. As emergence proceeds, these separate polarity regions start to merge and then break up, while in the corona sigmoidal structures form and a solar eruption occurs. We discuss what physical processes could be involved in the characteristic evolution of an active region magnetic field that leads to the formation of a sunspot surrounded by satellite polarity regions.

MAGNETIC HELICITY OF SOLAR ACTIVE REGIONS AND ITS IMPLICATIONS

  • SAKURAI T.;HAGINO M.
    • Journal of The Korean Astronomical Society
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    • v.36 no.spc1
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    • pp.7-12
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    • 2003
  • We have studied the magnetic helicity of active regions by using the data from (1) the photo-electric magnetograph of the Okayama Observatory (1983-1995) and (2) the video magnetograph of NAOJ/Mitaka (1992-2000). The latitude distribution of helicity showed a tendency that the regions in the north (south) hemisphere have negative (positive) helicities, respectively, which is already known as the hemispheric sign rule. If we look into the sign of helicity as a function of time, the sign rule was less definite or was reversed sometimes in the sunspot minimum phase. We also studied the relation between the magnetic helicity and the sunspot tilt angles, and found that these two quantities are positively correlated, which is opposite to the expectation of a theoretical model. The implications of this cycle-phase dependence of helicity signs and the correlation between magnetic he Ii city and sunspot tilt angles are discussed.

MAGNETIC HELICITY CHANGES OF SOLAR ACTIVE REGIONS BY PHOTOSPHERIC HORIZONTAL MOTIONS

  • MOON Y.-J.;CHAE JONGCHUL;PARK Y. D.
    • Journal of The Korean Astronomical Society
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    • v.36 no.spc1
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    • pp.37-44
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    • 2003
  • In this paper, we review recent studies on the magnetic helicity changes of solar active regions by photospheric horizontal motions. Recently, Chae(200l) developed a methodology to determine the magnetic helicity change rate via photospheric horizontal motions. We have applied this methodology to four cases: (1) NOAA AR 8100 which has a series of homologous X-ray flares, (2) three active regions which have four eruptive major X-ray flares, (3) NOAA AR 9236 which has three eruptive X-class flares, and (4) NOAA AR 8668 in which a large filament was under formation. As a result, we have found several interesting results. First, the rate of magnetic helicity injection strongly depends on an active region and its evolution. Its mean rate ranges from 4 to $17 {\times} 10^{40}\;Mx^2\;h^{-1}$. Especially when the homologous flares occurred and when the filament was formed, significant rates of magnetic helicity were continuously deposited in the corona via photospheric shear flows. Second, there is a strong positive correlation between the magnetic helicity accumulated during the flaring time interval of the homologous flares in AR 8100 and the GOES X-ray flux integrated over the flaring time. This indicates that the occurrence of a series of homologous flares is physically related to the accumulation of magnetic helicity in the corona by photospheric shearing motions. Third, impulsive helicity variations took place near the flaring times of some strong flares. These impulsive variations whose time scales are less than one hour are attributed to localized velocity kernels around the polarity inversion line. Fourth, considering the filament eruption associated with an X1.8 flare started about 10 minutes before the impulsive variation of the helicity change rate, we suggest that the impulsive helicity variation is not a cause of the eruptive solar flare but its result. Finally, we discuss the physical implications on these results and our future plans.

A NEAR-INFRARED STUDY OF THE HIGHLY-OBSCURED ACTIVE STAR-FORMING REGION W51B

  • Kim, Hyo-Sun;Nakajima, Yasushi;Sung, Hwan-Kyung;Moon, Dae-Sik;Koo, Bon-Chul
    • Journal of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.17-28
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    • 2007
  • We present wide-field $JHK_s$-band photometric observations of the three compact H II regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming region W51B. The star clusters inside the three compact H II regions show the excess number of stars in the $J-K_s$ histograms compared with reference fields. While the mean color excess ratio $(E_{J-H}/E_{H-K_s})$ of the three compact H II regions are similar to ${\sim}2.07$, the visual extinctions toward them are somewhat different: ${\sim}17$ mag for G48.9-0.3 and G49.0-0.3; ${\sim}23$ mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact H II region is ${\leq}2\;Myr$. The inferred total stellar mass, ${\sim}1.4{\times}10^4M_{\odot}$, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of ${\sim}10%$.

AN INVERSION METHOD FOR DERIVING PHYSICAL PROPERTIES OF A SUBSURFACE MAGNETIC FIELD FROM SURFACE MAGNETIC FIELD EVOLUTION I. APPLICATION TO SIMULATED DATA

  • Magara, Tetsuya
    • Journal of The Korean Astronomical Society
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    • v.50 no.6
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    • pp.179-184
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    • 2017
  • We present a new method for solving an inverse problem of flux emergence which transports subsurface magnetic flux from an inaccessible interior to the surface where magnetic structures may be observed to form, such as solar active regions. To make a quantitative evaluation of magnetic structures having various characteristics, we derive physical properties of subsurface magnetic field that characterize those structures formed through flux emergence. The derivation is performed by inversion from an evolutionary relation between two observables obtained at the surface, emerged magnetic flux and injected magnetic helicity, the former of which provides scale information while the latter represents the configuration of magnetic field.

MULTIPLE FLUX SYSTEMS AND THEIR WINDING ANGLES IN HALO CME SOURCE REGIONS

  • Kim, Hye- Rim;Moon, Y.J.;Jang, Min-Hwan;Kim, R.S.;Kim, Su-Jin;Choe, G.S.
    • Journal of The Korean Astronomical Society
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    • v.41 no.6
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    • pp.181-186
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    • 2008
  • Recently, Choe & Cheng (2002) have demonstrated that multiple magnetic flux systems with closed configurations can have more magnetic energy than the corresponding open magnetic fields. In relation to this issue, we have addressed two questions: (1) how much fraction of eruptive solar active regions shows multiple flux system features, and (2) what winding angle could be an eruption threshold. For this investigation, we have taken a sample of 105 front-side halo CMEs, which occurred from 1996 to 2001, and whose source regions were located near the disk center, for which magnetic polarities in SOHO/MDI magnetograms are clearly discernible. Examining their soft X-ray images taken by Yohkoh SXT in pre-eruption stages, we have classified these events into two groups: multiple flux system events and single flux system events. It is found that 74% (78/105) of the sample events show multiple flux system features. Comparing the field configuration of an active region with a numerical model, we have also found that the winding angle of the eruptive flux system is slightly above $1.5{\pi}$.

Face detection using active contours

  • Chang, Jae-Sik;Lee, Mu-Youl;Moon, Chae-Hyun;Park, Hye-Sun;Lee, Kyung-Mi;Kim, Hang-Joon
    • Proceedings of the IEEK Conference
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    • pp.1515-1518
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    • 2002
  • This paper proposes an active contour model to detect facial regions in a given image. Accordingly we use the color information human faces which is represented by a skin color model. We evolve the active contour using the level set method which allows for cusps, corners, and automatic topological changes. Experimental results show the effectiveness of the proposed method.

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STUDY OF SOLAR ACTIVE REGIONS BASED ON BOAO VECTOR MAGNETOGRAMS

  • MOON YONG-JAE;PARK YOUNG DEUK;YUN HONG SIK;CHO EUN-AH
    • Journal of The Korean Astronomical Society
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    • v.32 no.2
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    • pp.127-136
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    • 1999
  • In this study we present the study of solar active regions based on BOAO vector magnetograms and H$\alpha$ filtergrams. With the new calibration method we analyzed BOAO vector magnetograms taken from the SOFT observational system to compare with those of other observing systems. In this study it has been demonstrated that (1) our longitudinal magnetogram matches very well the corresponding Mitaka's magnetogram to the extent that the maximum correlation yields r=0.962 between our re-scaled longitudinal magnetogram and the Mitaka's magnetogram; (2) according to a comparison of our magnetograms of AR 8422 with those taken at Mitaka solar observatory their longitudinal fields are very similar to each other while transverse fields are a little different possibly due to large noise level; (3) main features seen by our longitudinal magnetograms of AR 8422 and AR 8419 and the corresponding Kitt Peak magnetograms are very similar to each other; (4) time series of our vector magnetograms and H-alpha observations of AR 8419 during its flaring (M3.1/1B) activity show that the filament eruption followed the sheared inversion line of the quadrupolar configuration of sunspots, indicating that the flare should be associated with the quadrupolar field configuration and its interaction with new filament eruption. Finally, it may be concluded that the Solar Flare Telescope at BOAO works normally and it is ready to do numerous observational and theoretical works associated with solar activities such as flares.

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