• Title, Summary, Keyword: chromosphere

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A Comprehensive View of Three-minute Umbral Oscillations

  • Chae, Jongchul;Cho, Kyuhyoun;Kang, Juhyeong;Kwak, Hannah;Lee, Kyeore
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.2
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    • pp.40.3-40.3
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    • 2019
  • Our recent observations of the Sun through strong spectral lines have revealed several important properties of the three-minute umbral oscillations inside sunspots -- the oscillations of intensity and Doppler velocity with periods of 2 to 3 minutes. The oscillations usually occur in the form of a time series of oscillation packets each of which lasts 10 to 20 minutes, not as continuous trains. Each oscillation packet is characterized by a singly peaked power spectrum of velocity oscillation. The oscillations propagate in the vertical direction from the photosphere to the corona. In the upper chromosphere, they develop into shocks that eventually collide with the transition region. When shocks propagate along a highly inclined direction, the merging of two successive shocks can take place. Once they enter the corona, they change to linear compressional waves. In the image plane, the three-minute oscillations propagate with high speeds in the transverse direction as well, usually propagating radially outwards from a point, and sometimes accompanying spiraling patterns of Doppler velocity. These observational properties can be theoretically explained by postulating the spatio-temporally localized source of fast MHD waves at a depth of about 2000 km below the surface, the excitation of slow MHD waves via mode conversion near the photosphere, and the resonance of the slow waves in the photospheric layer below the temperature minimum, and the nonlinear development of slow waves in the chromosphere.

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Image Translation of SDO/AIA Multi-Channel Solar UV Images into Another Single-Channel Image by Deep Learning

  • Lim, Daye;Moon, Yong-Jae;Park, Eunsu;Lee, Jin-Yi
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.2
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    • pp.42.3-42.3
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    • 2019
  • We translate Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) ultraviolet (UV) multi-channel images into another UV single-channel image using a deep learning algorithm based on conditional generative adversarial networks (cGANs). The base input channel, which has the highest correlation coefficient (CC) between UV channels of AIA, is 193 Å. To complement this channel, we choose two channels, 1600 and 304 Å, which represent upper photosphere and chromosphere, respectively. Input channels for three models are single (193 Å), dual (193+1600 Å), and triple (193+1600+304 Å), respectively. Quantitative comparisons are made for test data sets. Main results from this study are as follows. First, the single model successfully produce other coronal channel images but less successful for chromospheric channel (304 Å) and much less successful for two photospheric channels (1600 and 1700 Å). Second, the dual model shows a noticeable improvement of the CC between the model outputs and Ground truths for 1700 Å. Third, the triple model can generate all other channel images with relatively high CCs larger than 0.89. Our results show a possibility that if three channels from photosphere, chromosphere, and corona are selected, other multi-channel images could be generated by deep learning. We expect that this investigation will be a complementary tool to choose a few UV channels for future solar small and/or deep space missions.

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Ca II Transient Brightenings associated with Canceling Magnetic Features

  • Park, So-Young;Chae, Jong-Chul
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.96.2-96.2
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    • 2011
  • We analyzed transient Ca II brightening associated with small-scale canceling magnetic features in the quiet Sun near disk center using Ca II H and NaD1 filter images of the SOT/Hinode. We found that in most Ca II brightening related to CMFs the Ca II intensity peaks after magnetic flux cancellation proceeds. Moreover, brightening tend to appear as pairs of bright points of similar size and similar brightness overlying magnetic bipoles. These results imply that magnetic reconnection taking place in the chromosphere or above may be in charge of CMFs.

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NST/FISS Observations of Ellerman bombs and Surges

  • Yang, Heesu;Chae, Jongchul
    • The Bulletin of The Korean Astronomical Society
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    • v.38 no.2
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    • pp.86.2-86.2
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    • 2013
  • Ellerman bombs(EBs) are emission features at the wings of the H alpha spectral line. They are believed to be a kind of a magnetic reconnection feature in the low chromosphere or near photosphere. It was previously reported that surges often occur in association with EBs. However, previous observations were restricted to imaging observation. Using Fast Imaging Solar Spectrograph installed in New Solar Telescope at Big Bear Solar Observatory, California, we observed 5 EBs and associated surges with high-spatial and high-spectral resolutions. In this presentation, we will show the results and discuss the physical properties.

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Discovery of highly dynamic and recurrent jets in a polar coronal hole observed by Hinode/SOT

  • Cho, Il-Hyun;Moon, Yong-Jae;Cho, Kyung-Suk
    • 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.

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DEVELOPMENT OF THE FAST IMAGING SOLAR SPECTROGRAPH FOR 1.6 m NEW SOLAR TELESCOPE (1.6 m 신태양망원경용 고속영상태양분광기 개발)

  • Nah, Ja-Kyoung;Chae, Jong-Chul;Park, Young-Deuk;Park, Hyung-Min;Jang, Bi-Ho;Ahn, Kwang-Su;Yang, Hee-Su;Cho, Kyung-Suk;Kim, Yeon-Han;Kim, Kwang-Dong;Cao, Wenda;Gorceix, Nicolas;Goode, Philip. R.
    • Publications of The Korean Astronomical Society
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    • v.26 no.1
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    • pp.45-54
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    • 2011
  • KASI and Seoul National University developed the Fast Imaging Solar Spectrograph (FISS) as one of major scientific instruments for the 1.6 m New Solar Telescope (NST) and installed it in the Coude room of the NST at Big Bear Solar Observatory (BBSO) in May, 2010. The major objective of the FISS is to study the fine-scale structures and dynamics of plasma in the photosphere and chromosphere. To achieve it, the FISS is required to take data with a spectral resolution higher than $10^5$ at the spectrograph mode and a temporal resolution less than 10 seconds at the imaging mode. The FISS is a spectrograph using Echelle grating and has characteristics that can observe dual bands (H${\alpha}$ and CaII 8542) simultaneously and perform fast imaging using fast raster scan and two fast CCD cameras. In this paper, we introduce briefly the whole process of FISS development from the requirement analysis to the first observations.

AN INTERFERENCE FRINGE REMOVAL METHOD BASED ON MULTI-SCALE DECOMPOSITION AND ADAPTIVE PARTITIONING FOR NVST IMAGES

  • Li, Yongchun;Zheng, Sheng;Huang, Yao;Liu, Dejian
    • Journal of The Korean Astronomical Society
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    • v.52 no.2
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    • pp.49-55
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    • 2019
  • The New Vacuum Solar Telescope (NVST) is the largest solar telescope in China. When using CCDs for imaging, equal-thickness fringes caused by thin-film interference can occur. Such fringes reduce the quality of NVST data but cannot be removed using standard flat fielding. In this paper, a correction method based on multi-scale decomposition and adaptive partitioning is proposed. The original image is decomposed into several sub-scales by multi-scale decomposition. The region containing fringes is found and divided by an adaptive partitioning method. The interference fringes are then filtered by a frequency-domain Gaussian filter on every partitioned image. Our analysis shows that this method can effectively remove the interference fringes from a solar image while preserving useful information.