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Explaining the vanishing high-frequency phase delays of chromospheric diagnostics

Presentation #105.04 in the session Ambient Solar Atmosphere Posters.

Published onSep 18, 2023
Explaining the vanishing high-frequency phase delays of chromospheric diagnostics

Phase delays between spectral line features formed at different heights in the solar atmosphere are a diagnostic of vertically propagating disturbances. There has been a long standingquestion why high-frequency (above about 10 mHz)phase delays between Doppler velocity diagnostics formed in the photosphere and chromosphere of the quiet sun go to zero, whereas at lower frequencies around 5-10 mHz, still above the acoustic cutoff, exhibit the expected signatures of propagating acoustic waves. One possible explanation is that the phase speeds of these types of waves are significantly higher than their lower frequencycounterparts, or that there is enhanced wave damping at the higher frequencies.We address this question by examining the propagation of waves in MURaM radiative magnetohydrodynamic (rMHD) models of the solaratmosphere. In particular, we extend the previous work by Fleck et al. (2021) by using rMHD models extending into the chromosphere and the corona. We synthesize observable diagnostics (Fe I photospheric lines, Ca II IRtriplet, Na I D lines, and the Mg II h&k lines) with the RH15D code from these models. Based on the synthetic observables we explore possible explanation of the the vanishing high-frequency phase delay connundrum. We also attempt to address this question by using non-LTE inversions to look for signs of vertically propagating waves. We show the limitations of this type of inversions for wave studies in the chromosphere.

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