Impact of opacity effects on chromospheric oscillations inferred from NLTE inversions

Context. Spectropolarimetric inversions are a fundamental tool for diagnosing the solar atmosphere. Chromospheric inferences rely on interpretation of spectral lines that formed under nonlocal thermodynamic equilibrium (NLTE) conditions. In presence oscillations, changes in opacity impact response height and hinder determination real properties fluctuations. Aims. We aim to explore relationship between chromospheric oscillations inferred by NLTE inversion codes intrinsic fluctuations velocity temperature produced waves. Methods. computed numerical simulations wave propagation sunspot umbra with code MANCHA. used synthesis NICOLE compute spectropolarimetric Ca II 8542 Å line profiles atmospheric models obtained as output from simulations. then inverted synthetic compared known atmospheres Results. capture low-frequency including those main band around 6 mHz. contrast, waves frequencies above 9 mHz poorly characterized results. Velocity at higher exhibit clear signs fluctuations; namely power signal constant optical depth greatly departs geometrical height. The comes low heights, whereas shows sudden jumps high photosphere chromosphere. This strong variation where is sensitive revealed oscillatory fluctuations, which much stronger than actual oscillations. Conclusions. Our results validate use study below ∼9 However, higher-frequency must be addressed care, these signatures