Influence of the Conversion Layer on the Dispersion Relation of Waves in the Solar Atmosphere

TL;DR

This study investigates how the conversion layer affects wave dispersion in the solar atmosphere, revealing differences in magnetic and non-magnetic regions and suggesting mode conversion processes.

Contribution

It provides observational evidence of dispersion relation variations and proposes partial mode conversion as an explanation for observed wave behaviors.

Findings

Significant differences in dispersion relations between magnetic and non-magnetic regions.

No evidence of slow acoustic mode at the conversion layer.

Possible partial mode conversion from fast acoustic to fast magnetic waves.

Abstract

Observations carried out with the Magneto-Optical Filter at Two Heights (MOTH) experiment show upward-traveling wave packets in magnetic regions with frequencies below the acoustic cut-off. We demonstrate that the frequency dependence of the observed travel times, i.e. the dispersion relation shows significant differences in magnetic and non-magnetic regions. More importantly, at and above the layer where the Alfven speed equals the sound speed we do not see the dispersion relation of the slow acoustic mode with a lowered cut-off frequency. Our comparisons with theoretical dispersion relations do not suggest this is the slow acoustic wave type for the upward low-frequency wave. From this we speculate that partial mode conversion from the fast acoustic to the fast magnetic wave might take place.