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Title: Photospheric Origin of Three-minute Oscillations in a Sunspot

Abstract

The origin of the three-minute oscillations of intensity and velocity observed in the chromosphere of sunspot umbrae is still unclear. We investigated the spatio-spectral properties of the 3 minute oscillations of velocity in the photosphere of a sunspot umbra as well as those in the low chromosphere using the spectral data of the Ni i λ 5436, Fe i λ 5435, and Na i D{sub 2} λ 5890 lines taken by the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope at the Big Bear Solar Observatory. As a result, we found a local enhancement of the 3 minute oscillation power in the vicinities of a light bridge (LB) and numerous umbral dots (UDs) in the photosphere. These 3 minute oscillations occurred independently of the 5 minute oscillations. Through wavelet analysis, we determined the amplitudes and phases of the 3 minute oscillations at the formation heights of the spectral lines, and they were found to be consistent with the upwardly propagating slow magnetoacoustic waves in the photosphere with energy flux large enough to explain the chromospheric oscillations. Our results suggest that the 3 minute chromospheric oscillations in this sunspot may have been generated by magnetoconvection occurring in themore » LB and UDs.« less

Authors:
; ; ;  [1]; ;  [2]
  1. Astronomy Program, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826 (Korea, Republic of)
  2. Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22663879
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; CHROMOSPHERE; HYDRODYNAMICS; IRON; MAGNETIC FIELDS; MAGNETOACOUSTIC WAVES; MAGNETOACOUSTICS; NICKEL; OSCILLATIONS; PHOTOSPHERE; SODIUM; SPECTRA; SUN; SUNSPOTS; TELESCOPES; VELOCITY; VISIBLE RADIATION

Citation Formats

Chae, Jongchul, Lee, Jeongwoo, Cho, Kyuhyoun, Song, Donguk, Cho, Kyungsuk, and Yurchyshyn, Vasyl. Photospheric Origin of Three-minute Oscillations in a Sunspot. United States: N. p., 2017. Web. doi:10.3847/1538-4357/836/1/18.
Chae, Jongchul, Lee, Jeongwoo, Cho, Kyuhyoun, Song, Donguk, Cho, Kyungsuk, & Yurchyshyn, Vasyl. Photospheric Origin of Three-minute Oscillations in a Sunspot. United States. doi:10.3847/1538-4357/836/1/18.
Chae, Jongchul, Lee, Jeongwoo, Cho, Kyuhyoun, Song, Donguk, Cho, Kyungsuk, and Yurchyshyn, Vasyl. Fri . "Photospheric Origin of Three-minute Oscillations in a Sunspot". United States. doi:10.3847/1538-4357/836/1/18.
@article{osti_22663879,
title = {Photospheric Origin of Three-minute Oscillations in a Sunspot},
author = {Chae, Jongchul and Lee, Jeongwoo and Cho, Kyuhyoun and Song, Donguk and Cho, Kyungsuk and Yurchyshyn, Vasyl},
abstractNote = {The origin of the three-minute oscillations of intensity and velocity observed in the chromosphere of sunspot umbrae is still unclear. We investigated the spatio-spectral properties of the 3 minute oscillations of velocity in the photosphere of a sunspot umbra as well as those in the low chromosphere using the spectral data of the Ni i λ 5436, Fe i λ 5435, and Na i D{sub 2} λ 5890 lines taken by the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope at the Big Bear Solar Observatory. As a result, we found a local enhancement of the 3 minute oscillation power in the vicinities of a light bridge (LB) and numerous umbral dots (UDs) in the photosphere. These 3 minute oscillations occurred independently of the 5 minute oscillations. Through wavelet analysis, we determined the amplitudes and phases of the 3 minute oscillations at the formation heights of the spectral lines, and they were found to be consistent with the upwardly propagating slow magnetoacoustic waves in the photosphere with energy flux large enough to explain the chromospheric oscillations. Our results suggest that the 3 minute chromospheric oscillations in this sunspot may have been generated by magnetoconvection occurring in the LB and UDs.},
doi = {10.3847/1538-4357/836/1/18},
journal = {Astrophysical Journal},
number = 1,
volume = 836,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2017},
month = {Fri Feb 10 00:00:00 EST 2017}
}
  • Three-minute oscillations over a sunspot's umbra in AR 11131 were observed simultaneously in UV/EUV emission by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and in radio emission by the Nobeyama Radioheliograph (NoRH). We use 24 hr series of SDO and 8 hr series of NoRH observations to study spectral, spatial, and temporal variations of pulsations in the 5-9 mHz frequency range at different layers of the solar atmosphere. High spatial and temporal resolution of SDO/AIA in combination with long-duration observations allowed us to trace the variations of the cutoff frequency and spectrum of oscillations across the umbra. We foundmore » that higher frequency oscillations are more pronounced closer to the umbra's center, while the lower frequencies concentrate on the peripheral parts. We interpreted this discovery as a manifestation of variation of the magnetic field inclination across the umbra at the level of temperature minimum. Possible implications of this interpretation for the diagnostics of sunspot atmospheres are discussed.« less
  • Using data of the Harvard--Smithsonian Reference Atmosphere'' (Gingerich et al., 1971), the eigenfrequencies of the solar atmosphere were recalculated. Comment is made on two different proposals made by several investigators to explain the nature of the 5-min oscillations. Uchida (1965) and Thomas (1971) suggested that the oscillations are internal gravity waves. Acoustic waves with periods longer than the photospheric cutoff can propagate in the subphotospheric region. The most appealing property of subphotospheric oscillations maintained by one of the mechanisms discussed would be their coherence over large regions and long time intervals. (IAA)
  • In this Letter we report the detection of chromospheric 3-minute oscillations in disk-integrated EUV irradiance observations during a solar flare. A wavelet analysis of detrended Ly α (from GOES /EUVS) and Lyman continuum (from Solar Dynamics Observatory ( SDO )/EVE) emission from the 2011 February 15 X-class flare (SOL2011-02-15T01:56) revealed a ∼3 minute period present during the flare’s main phase. The formation temperature of this emission locates this radiation at the flare’s chromospheric footpoints, and similar behavior is found in the SDO /Atmospheric Imaging Assembly 1600 and 1700 Å channels, which are dominated by chromospheric continuum. The implication is thatmore » the chromosphere responds dynamically at its acoustic cutoff frequency to an impulsive injection of energy. Since the 3-minute period was not found at hard X-ray (HXR) energies (50–100 keV) in Reuven Ramaty High Energy Solar Spectroscopic Imager data we can state that this 3-minute oscillation does not depend on the rate of energization of non-thermal electrons. However, a second period of 120 s found in both HXR and chromospheric lightcurves is consistent with episodic electron energization on 2-minute timescales. Our finding on the 3-minute oscillation suggests that chromospheric mechanical energy should be included in the flare energy budget, and the fluctuations in the Ly α line may influence the composition and dynamics of planetary atmospheres during periods of high activity.« less
  • The vertical propagation of nonlinear acoustic waves in an isothermal atmosphere is considered. A new analytical solution that describes a finite-amplitude wave of an arbitrary wavelength is obtained. Although the short- and long-wavelength limits were previously considered separately, the new solution describes both limiting cases within a common framework and provides a straightforward way of interpolating between the two limits. Physical features of the nonlinear waves in the chromosphere are described, including the dispersive nature of low-frequency waves, the steepening of the wave profile, and the influence of the gravitational field on wavefront breaking and shock formation. The analytical resultsmore » suggest that observations of three-minute oscillations in the solar chromosphere may reveal the basic nonlinear effect of oscillations with combination frequencies, superposed on the normal oscillations of the system. Explicit expressions for a second-harmonic signal and the ratio of its amplitude to the fundamental harmonic amplitude are derived. Observational evidence of the second harmonic, obtained with the Fast Imaging Solar Spectrograph, installed at the 1.6 m New Solar Telescope of the Big Bear Observatory, is presented. The presented data are based on the time variations of velocity determined from the Na i D{sub 2} and H α lines.« less