Peculiarity of the oscillation stratification in sunspot penumbrae

TL;DR

This study reveals that the inner penumbra of sunspots consistently favors 2.5-4 mHz oscillation propagation across multiple atmospheric heights, indicating similar physical conditions from the photosphere to the transition region.

Contribution

It demonstrates that the dominant oscillation frequency in sunspot inner penumbrae is consistent across different atmospheric layers, extending previous findings to higher altitudes.

Findings

Inner penumbrae favor 2.5-4 mHz oscillations

Similar spectral composition across atmospheric heights

Consistent physical conditions from photosphere to transition region

Abstract

Spatial distributions of the dominant oscillation frequency obtained for four sunspots show a feature shared by all the analysed levels of the solar atmosphere in these sunspots. This feature located in the inner penumbrae indicates that this region has favourable conditions for 2.5-4 mHz oscillation propagation. This agrees with the fact that the spectral composition of the oscillations at three atmospheric heights (FeI 6173{\AA}, 1700{\AA}, and He II 304{\AA}) in this region are similar. There have been previous evidence of particular similarities along height of photospheric magnetic field strength, line-of-sight velocity, and temperature profile in the inner penumbra, where the internal boundary of the Evershed flow is located. The finding of the same dominant oscillation frequency at a range of altitudes from the chromosphere up to the transition region extends the height range, suggesting similarities in physical conditions.