Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI
S. JafarzadehS. K. SolankiR. GafeiraM. van NoortP. BartholJ. Blanco RodríguezJ. C. del Toro IniestaA. GandorferL. GizonJ. HirzbergerM. KnölkerD. Orozco SuárezT. L. RiethmüllerW. Schmidt
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We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution seeing-free observations in a 0.11 nm wide passband covering the line core of Ca II H 396.9 nm from the second flight of the Sunrise balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4+-0.8 km/s and 83+-29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9+-14 km/s. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvenic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid high-frequency transverse waves, often produced in the lower photosphere, can penetrate into the chromosphere with an estimated energy flux of ~ 15 kW/m^2. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.Keywords:
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Context.Ca bright grains are small and repetitive brightenings ubiquitously found in the quiet Sun.Aims.The relationship between the formation of Ca bright grains and the dynamics in the chromosphere and the photosphere is studied.Methods.We simultaneously observed the time series of spectra in Ca II H, Hα, and Fe I with the horizontal spectrograph of the Domeless Solar Telescope (DST) at Hida Observatory.Results.Our wavelet analysis revealed that the occurrence of Ca II H brightenings are correlated with enhanced 5 mHz velocity oscillations in the chromosphere and the photosphere.Conclusions.Ca bright grains can be explained by acoustic shocks in the chromosphere that are associated with 5 mHz oscillations in the photosphere below.
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view Abstract Citations (514) References (97) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Structure of the solar chromosphere. II. The underlying photosphere and temperature-minimum region. Vernazza, J. E. ; Avrett, E. H. ; Loeser, R. Abstract The paper presents a non-LTE empirical model of the quiet solar photosphere and the temperature-minimum region. The continuous spectrum computed from this model is in good overall agreement with available disk-center observations throughout the wavelength range from 0.125 to 500 microns. It is found that (1) absolute-intensity measurements are needed in the range between 1 and 2 microns to establish the structure of the deepest observable layers; (2) absolute-intensity or flux measurements are needed in the range between 20 and 200 microns to determine whether the minimum solar temperature occurring between the photosphere and the chromosphere is as low as indicated by present observations or much higher, as recent theoretical predictions indicate; (3) studies of the far-ultraviolet spectrum based on the assumption of LTE can be substantially in error; and (4) line opacity seems to account for the 'missing opacity' in the ultraviolet. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1976 DOI: 10.1086/190356 Bibcode: 1976ApJS...30....1V Keywords: Chromosphere; Photosphere; Solar Atmosphere; Solar Spectra; Solar Temperature; Astronomical Models; Continuous Spectra; Infrared Spectra; Stellar Structure; Ultraviolet Spectra; Solar Physics full text sources ADS |
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Context. The Ca ii H line is one of the strongest lines in the solar spectrum, and it provides continuous information on the solar atmosphere from the photosphere to the lower chromosphere.
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Composition observations, in the solar photosphere, and in the upper transition region (TR) and corona imply a change of composition of the solar atmosphere somewhere between the photosphere and the upper TR. Heavy elements with first ionization potential (FIP) 9 eV (high-FIP element) are approx. 4 times less abundant in the TR and corona than in the photosphere, as compared to both hydrogen and heavy elements with lower low-FIP elements. A separation is suggested between neutral and ionized elements in a region where the high-FIP elements are mostly neutral, and the low-FIP elements ionized. This occurs in the chromosphere at altitudes above 600 km and below 2000 km above Photosphere. Whether the diffusion processes can explain the observed change in composition is investigated.
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view Abstract Citations (67) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Sunspot umbral oscillations in the photosphere and low chromosphere Lites, B. W. ; Thomas, J. H. Abstract In the present simultaneous measurement of sunspot umbrae velocity oscillations in one spectral line formed in the low photosphere, and in another formed in the low chromosphere, just above the temperature minimum, the velocity power spectrum in each is found to exhibit both 5-min and 3-min oscillations, with the kinetic energy of the latter being at least 5 times greater in the low photosphere than in the low chromosphere. The 3-min umbral oscillation has the character of a coherent, vertically standing wave in the photosphere. These results imply a photospheric, rather than chromospheric, resonant origin for the fundamental 3-min umbral oscillation. A negative phase difference at frequencies around 2 mHz suggests the presence of gravity waves in the umbra. Publication: The Astrophysical Journal Pub Date: July 1985 DOI: 10.1086/163338 Bibcode: 1985ApJ...294..682L Keywords: Chromosphere; Photosphere; Solar Atmosphere; Solar Oscillations; Sunspots; Umbras; Kinetic Energy; Line Spectra; Power Spectra; Solar Physics full text sources ADS |
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