A Hot Downflowing Model Atmosphere For Umbral Flashes And The Physical Properties Of Their Dark Fibrils

Abstract

We perform NLTE inversions in a large set of umbral flashes, including the dark fibrils visible within them, and in the quiescent umbra by using the inversion code NICOLE on a set of full Stokes high-resolution Ca II 8542 A observations of a sunspot at disk center. We find that the dark structures have Stokes profiles that are distinct from those of the quiescent and flashed regions. They are best reproduced by atmospheres that are more similar to the flashed atmosphere in terms of velocities, even if with reduced amplitudes. We also find two sets of solutions that finely fit the flashed profiles: a set that is upflowing, featuring a transition region that is deeper than in the quiescent case and preceded by a slight dip in temperature, and a second solution with a hotter atmosphere in the chromosphere but featuring downflows close to the speed of sound at such heights. Such downflows may be related, or even dependent, on the presence of coronal loops, rooted in the umbra of sunspots, as is the case in the region analyzed. Similar loops have been recently observed to have supersonic downflows in the transition region and are consistent with the earlier "sunspot plumes" which were invariably found to display strong downflows in sunspots. Finally we find, on average, a magnetic field reduction in the flashed areas, suggesting that the shock pressure is moving field lines in the upper layers.

Accepted in June for publication at ApJ. Comments to [email protected] or [email protected]

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• The Propagation of Coherent Waves Across Multiple Solar Magnetic Pores
• Transverse motions in sunspot super-penumbral fibrils
• The magnetic properties of photospheric magnetic bright points with high resolution spectropolarimetry
• Properties of shock waves in the quiet Sun chromosphere
• Downflowing umbral flashes as an evidence of standing waves in sunspot umbrae
• Limitations of the Ca II 8542 Å line for the determination of magnetic field oscillations
• Inversions of synthetic umbral flashes: selection of wavelength sampling
• Impact of opacity effects on chromospheric oscillations inferred from NLTE inversions
• Magnetic field fluctuations in the shocked umbral chromosphere
• Observations of umbral flashes in the resonant sunspot chromosphere
• Multi-wavelength spectropolarimetric observations of AR13724 performed by GRIS
• Chromospheric and photospheric properties of sunspots as inferred from Stokes inversions under magneto-hydrostatic and non-local-thermodynamic equilibrium