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Paper: Acoustic Shocks in the Quiet Solar Chromosphere
Volume: 368, The Physics of Chromospheric Plasmas
Page: 127
Authors: Cauzzi, G.; Reardon, K.P.; Vecchio, A.; Janssen, K.; Rimmele, T.
Abstract: We exploit the two-dimensional spectroscopic capabilities of the Interferometric BIdimensional Spectrometer (IBIS) to study the chromospheric Ca II 854.2nm line and its temporal evolution in a quiet region at the center of the solar disk. The Ca II 854.2 profiles in the internetwork portion of the field of view clearly indicate the presence of hydrodynamic shocks, occurring at frequencies above the acoustic cut-off. The location and strength of such shocks perfectly map the areas where large velocity power is found at frequencies of 5.58 mHz in a standard Fourier analysis. The shocks locations evidence a sharp partition of the quiet area in regions of very distinct dynamical behavior, highlighting the role of the local magnetic topology in structuring the lower chromosphere. The portions of the field of view where the photospheric field is very weak, and that are presumably connected to distant magnetic structures (or open to the interplanetary field), are the site of frequent shock occurrence. On the contrary, in regions neighboring the magnetic network and harboring a more horizontal configuration of the chromospheric magnetic field, shocks are heavily suppressed, even if the photospheric field is essentially absent in these areas as well. These latter regions, with much reduced velocity power at frequencies of 5.58 mHz (the “magnetic shadows” first described in Judge et al. 2001), are spatially coincident with fibrilar structures visible in the Ca II 854.2 line core intensity maps. We finally argue that areas within and immediately surrounding the magnetic network also display evidence of chromospheric shocks, but occurring at periodicities of 46 minutes. Such slow shocks are stronger than those occurring in field-free areas, as evidenced by the strong emission in the inner blue-wing of the line. This is in agreement with recent results claiming that magneto-acoustic shocks can develop in inclined magnetic structures, acting as ‘portals’ through which the powerful low-frequency photospheric oscillations can leak into the chromosphere.
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