• Title, Summary, Keyword: chromosphere

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A TWO CAVITY MODEL FOR UMBRAL OSCILLATIONS

  • Lee, Jeong-Woo;Yun, Hong-Sik
    • Journal of The Korean Astronomical Society
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    • v.20 no.1
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    • pp.27-47
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    • 1987
  • In the present study a two-mode, separately concurring resonant cavity model is proposed for theoretical interpretation of the 3 minute umbral oscillation. The proposed model has been investigated by calculating the transmission coefficients of the waves propagating through the umbral photosphere (photospheric weak-field cavity) and chromosphere (chromospheric strong-field cavity) into the corona, for 3 different umbral model atmospheres by Staude (1982), Beebe et al. (1982) and Avrett (1981). In computing the transmission coefficients we made use of multi-layer approximation by representing the umbra] atmosphere by a number of separate layers with (1) temperature varying linearly with depth and (2) temperature constant within each layer. The medium is assumed to be compressible, non-viscous, perfectly conducting under gravity. The computed resonant periods, transmission spectra, phase spectra, and kinetic energy density of the waves associated with the oscillations are presented in comparison with the observations and their model dependent characteristics are discussed.

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HEATING OF SUNSPOT CHROMOSPHERES BY SLOW-MODE ACOUSTIC SHOCK WAVES

  • Lee, Myung-Gyoon;Yun, Hong-Sik
    • Journal of The Korean Astronomical Society
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    • v.18 no.1
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    • pp.15-31
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    • 1985
  • Making use of the arbitrary shock theory developed by Ulmschneider (1967, 1971) and Ulmschneider and Kalkofen (1978), we have calculated the dissipation rates of upward-travelling slow-mode acoustic shock waves in umbral chromospheres for two umbral chromosphere models, a plateau model by Avrett (1981) and a gradient model by Yun and Beebe (1984). The computed shock dissipation rates are compared with the radiative cooling rate given by Avrett (1981). The results show that the slow-mode acoustic shock waves with a period of about 20 second can heat the low umbral chromospheres travelling with a mechanical energy flux of $2.6{\times}10^6\;erg/cm^2s$ at a height of $300{\sim}400km$ above the temperature minimum region.

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SUNSPOTS AND THEIR ASSOCIATED SOLAR ACTIVITIES I. PHYSICAL CHARACTERISTICS OF A WHITE LIGHT FLARE

  • LEE SANG-WOO;YUN HONG SIK
    • Journal of The Korean Astronomical Society
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    • v.28 no.1
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    • pp.77-87
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    • 1995
  • An attempt has been made to analyze time series of $H_\alpha,\;H_\beta,\;and\; H_\gamma$ line profiles taken from a 3B/X6.1 flare which occurred on Oct. 27, 1991 in an active region, NOAA 6891. A total of 22 sets of $H_\alpha,\;H_\beta,\;and\; H_\gamma$ taken with a low and non-uniform time resolution of 10-40 seconds were scanned by PDS with absolute intensity calibration to derive the physical characteristics of the material in the flare chromosphere. Our . results are as follows: (1) The lower Balmer lines observed during the flare activity are broadened by Stark effect. (2) At the peak of the flare activity, the electron temperature of the Balmer line emitting region reaches up to 35000K and its geometrical thickness increases to a scale of $10^4km$, suggesting that high energy particles penetrate deep into the photospheric level.

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COMMENTS ON MAGNETIC RECONNECTION MODELS OF CANCELING MAGNETIC FEATURES ON THE SUN

  • Litvinenko, Yuri E.
    • Journal of The Korean Astronomical Society
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    • v.48 no.3
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    • pp.187-190
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    • 2015
  • Data analysis and theoretical arguments support magnetic reconnection in a chromospheric current sheet as the mechanism of the observed photospheric magnetic flux cancellation on the Sun. Flux pile-up reconnection in a Sweet–Parker current sheet can explain the observed properties of canceling magnetic features, including the speeds of canceling magnetic fragments, the magnetic fluxes in the fragments, and the flux cancellation rates, inferred from the data. It is discussed how more realistic chromospheric reconnection models can be developed by relaxing the assumptions of a negligible current sheet curvature and a constant height of the reconnection site above the photosphere.

FISS Observation of Bright Rims of Solar Filaments

  • Yang, Hee-Su;Chae, Jong-Chul;Park, Hyung-Min;Song, Dong-Uk
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.97.2-97.2
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    • 2011
  • Rims of solar filaments often appear brighter than the background chromosphere, but their physical nature is still poorly known. Last year, we observed a filament with a bright rim. The rim was bright in H alpha but not in Ca II 8542 line. Using the cloud model, we inferred physical parameters of the region from the spectral profiles. As a result, we found that the Doppler width of the H alpha line is very large, which implies temperature as high as 50000K. In addition, the value of the source function of the H alpha line is 0.7 times the continuum intensity of background profile. These results suggest that the bright rims might be a region of intense heating, probably associated with a current sheet. To further investigate this possibility, we carried out more observations this summer. We will present new results obtained from the analysis of these observations and discuss the physical implication of these measurements on the nature of bright rims and the filaments.

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KINEMATICS OF SOLAR CHROMOSPHERIC SURGES OF AR 10930

  • Bong, Su-Chan;Cho, Kyung-Suk;Yurchyshyn, Vasyl
    • Journal of The Korean Astronomical Society
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    • v.47 no.6
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    • pp.311-317
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    • 2014
  • Solar chromospheric surges are often reported to contain rotational motion. However, the details of the motion and driving mechanism of the surges are not yet fully understood. Recurrent surges with rotational motion at AR 10930 on the west limb are observed by Hinode Solar Optical Telescope (SOT) continuously from 11:21 UT on December 18 to 09:58 UT on December 19, 2006, using the $Ca_{II}$ H broadband filter. We analyze details of the motion including number of turns from the rise of the surge to the fall, axial speed and acceleration. During the observation, rise and fall motion accompanying rotation appears recurrently. There occur a total of 14 surges at AR 10930 over 17 hours. The average duration is 45 minutes, and the average width, and length are 8 Mm, and 39 Mm, respectively. We speculate that the surges occurred by recurrent reconnections between the twisted prominence and large untwisted flux tube.

An Automated System for Empirical Forecasting of Solar Flares and CMEs

  • Park, Sung-Hong;Yamamoto, Tetsuya
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.2
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    • pp.129.2-129.2
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    • 2012
  • Solar flares and coronal mass ejections (CMEs) are two major solar eruptive phenomena which can cause enormous economic and commercial losses: (1) flares are sudden, rapid, and intense brightenings from radio waves to Gamma-rays in the chromosphere and corona, and (2) CMEs are large-scale transient eruptions of magnetized plasma from the solar corona that propagate outward into interplanetary space. Most flares and CMEs occur in magnetically complicated solar active regions (ARs). Therefore, it is crucial to investigate magnetic fields in ARs and their temporal variations for understanding a precondition and a trigger mechanism related to flare/CME initiation. In this presentation, we will introduce an automated system for empirical forecasting of flares and CMEs in ARs using full-disk photospheric line-of-sight magnetogram data taken by the Helioseismic and Magnetic Imager (HMI) onboard the SDO.

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The Response of the Solar Chromosphere and Transition Region to a Coronal Rain Event

  • Kwak, Hannah;Chae, Jongchul
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.83.4-84
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    • 2015
  • We report that a strong downflow event caused three-minute oscillations in the solar atmosphere. Our observations were carried out by using the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST) and the Interface Region Imaging Spectrograph (IRIS). Our main findings are as follows: (1) The strong downflow was seen at the $H{\alpha}$ absorption line at first, and then appeared at the Si IV and C II emission lines. It seems that the characteristics of the downflow are consistent with a coronal rain event. (2) After the event, oscillations of velocity were identified in the chromospheric lines and transition region lines. (3) The amplitudes of oscillations were 2km/s at Mg II line and 3km/s at C II and Si IV lines and decreased with time. (4) The period of the oscillation was 2.67 minutes at first, but gradually increased with time. Our findings are in agreement with Chae & Goode (2015)'s theory that of acoustic waves generated by a disturbance in a gravitationally-stratified medium.

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