Spectropolarimetric Investigation of the Propagation of Magnetoacoustic Waves and Shock Formation in Sunspot Atmospheres

By R. Centeno, Manel Collados, J. Trujillo Bueno. 2005

153 citations recorded by the source corpus.

Velocity oscillations in sunspot umbrae have been measured simultaneously in two spectral lines: the photospheric Si I λ10827 line and the chromospheric He I λ10830 multiplet. From the full Stokes inversion of temporal series of spectropolarimetric observations, we retrieved, among other parameters, the line-of-sight velocity temporal variations at photospheric and chromospheric heights. Chromospheric velocity oscillations show a 3 minute period with a clear sawtooth shape typical of propagating shock wave fronts. Photospheric velocity oscillations have basically a 5 minute period, although the power spectrum also shows a secondary peak in the 3 minute band that has been proven to be a predecessor for its chromospheric counterpart. The derived phase spectra yield a value of the atmospheric cutoff frequency around 4 mHz and give evidence for the upward propagation of higher frequency oscillation modes. The phase spectrum has been reproduced with a simple model of linear vertical propagation of slow magnetoacoustic waves in a stratified magnetized atmosphere that accounts for radiative losses through Newton's cooling law. The model explains the main features in the phase spectrum and allows us to compute the theoretical time delay between the photospheric and chromospheric signals, which happens to have a strong dependence on frequency. We find a very good agreement between this and the time delay obtained directly from the cross-correlation of photospheric and chromospheric velocity maps filtered around the 6 mHz band. This allows us to infer that the 3 minute power observed at chromospheric heights comes directly from the photosphere by means of linear wave propagation, rather than from nonlinear interaction of 5 minute (and/or higher frequency) modes.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/fb1291896f3c677aa3696f1eead771c32af159a5

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Citations in the corpus

Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects (2008, background): “…of plasma structures in the solar chromosphere and corona, such as active regions (e.g., Harvey & Hall 1971; Rüedi et al. 1996; Lagg et al. 2004; Centeno et al. 2006), filaments (e.g., Lin et al. 1998; Trujillo Bueno et al. 2002b), prominences (e.g., Merenda et al. 2006) and spicules (e.g.,…”
Oscillations and Waves in Sunspots (2015, methodology): “…observations of the umbra in the photosphere and chromosphere point toward the detection of slow magneto-acoustic waves propagating longitudinally along the magnetic field lines (Centeno et al., 2006; Felipe et al., 2010a; Bloomfield et al., 2007b,a; Jess et al., 2013), see Sections 2 and 3.”
Multiwavelength Studies of MHD Waves in the Solar Chromosphere (2015, background): “…waves, while others believe they are the observational signature of upwardly propagating magnetoacoustic waves guided along the intense magnetic fields of the underlying sunspot (Christopoulou et al. 2000, 2001; Georgakilas et al. 2000; Centeno et al. 2006; Tziotziou et al. 2006, 2007).”
Numerical Modeling of Magnetohydrodynamic Wave Propagation and Refraction in Sunspots (2006, background): “Recent IR observations in the 10830 8 spectral region analyzed by Centeno et al. (2006) reveal the photospheric counterpart of the 3 minute chromospheric oscillations.”