Vertical Propagation of Acoustic Waves in the Solar Inter-Network as Observed by IRIS

TL;DR

This study uses IRIS observations to analyze how acoustic waves propagate vertically through the solar atmosphere, revealing that certain oscillations successfully travel from the photosphere to the transition region, with some influenced by magnetic fields.

Contribution

First detailed analysis of acoustic wave propagation from photosphere to transition region in quiet Sun using IRIS spectral data, highlighting the role of magnetic fields.

Findings

70% coherence between photosphere and chromosphere at certain locations

3-minute oscillations originate in the photosphere and propagate upward

5-minute oscillations can propagate downward or upward depending on conditions

Abstract

We investigate the Interface Region Imaging Spectrograph (IRIS) observations of the quiet-Sun (QS) to understand the propagation of acoustic waves in transition region (TR) from photosphere. We selected a few IRIS spectral lines, which include the photospheric (Mn~{\sc i} 2801.25~{\AA}), chromospheric (Mg~{\sc ii} k 2796.35~{\AA}) and TR (C~{\sc ii} 1334.53~{\AA}), to investigate the acoustic wave propagation.The wavelet cross-spectrum reveals significant coherence (about 70\% locations) between photosphere and chromosphere. Few minutes oscillations (i.e., period range from 1.6 to 4.0 minutes) successfully propagate into chromosphere from photosphere, which is confirmed by dominance of positive phase lags. However, in higher period regime (i.e., greater than $\approx$ 4.5 minutes), the downward propagation dominates is evident by negative phase lags. The broad spectrum of waves (i.e., 2.5-6.0 minutes) propagates freely upwards from chromosphere to TR. We find that only about 45\% locations (out of 70\%) show correlation between chromosphere and TR. Our results indicate that roots of 3 minutes oscillations observed within chromosphere/TR are located in photosphere. Observations also demonstrate that 5 minute oscillations propagate downward from chromosphere. \textbf{However, some locations within QS also show successful propagation of 5 minute oscillations as revealed by positive phase lags, which might be the result of magnetic field}. In addition, our results clearly show that a significant power, within period ranging from 2.5 to 6.0 minutes, of solar chromosphere is freely transmitted into TR triggering atmospheric oscillations. Theoretical implications of our observational results are discussed.