Magneto-acoustic waves in sunspots from observations and numerical simulations

TL;DR

This study combines observations and numerical simulations to analyze magneto-acoustic wave propagation in sunspots, revealing the nature of standing and propagating waves and modeling their behavior across different atmospheric layers.

Contribution

It introduces a combined observational and numerical approach to study wave propagation in sunspots, providing insights into wave behavior and sunspot atmospheric structure.

Findings

Standing waves below 4 mHz and propagating waves above 4 mHz identified.

Numerical simulations successfully replicate observed wave features.

Waves are confirmed as slow MHD waves traveling along magnetic field lines.

Abstract

We study the propagation of waves from the photosphere to the chromosphere of sunspots. From time series of cospatial Ca II H (including its line blends) intensity spectra and polarimetric spectra of Si I 1082.7 nm and He I 1083.0 nm we retrieve the line-of-sight velocity at several heights. The analysis of the phase difference and amplification spectra shows standing waves for frequencies below 4 mHz and propagating waves for higher frequencies, and allows us to infer the temperature and height where the lines are formed. Using these observational data, we have constructed a model of sunspot, and we have introduced the velocity measured with the photospheric Si I 1082.7 nm line as a driver. The numerically propagated wave pattern fits reasonably well with the observed using the lines formed at higher layers, and the simulations reproduce many of the observed features. The observed waves are slow MHD waves propagating longitudinally along field lines.