Effect of area divergence and frequency on damping of slow magnetoacoustic waves propagating along umbral fan loops

TL;DR

This study investigates how area divergence and wave frequency influence the damping of slow magnetoacoustic waves propagating along solar fan loops, revealing frequency-dependent damping and the significance of area divergence in wave energy dissipation.

Contribution

It provides the first detailed analysis of the combined effects of area divergence and wave frequency on SMAW damping from the photosphere to corona.

Findings

Damping lengths are approximately 170-208 km for 1.5-3 min waves.

Area divergence increases actual damping lengths.

High-frequency waves damp faster than low-frequency waves.

Abstract

Waves play an important role in the heating of solar atmosphere, however, observations of wave propagation and damping from the solar photosphere to corona through chromosphere and transition region are very rare. Recent observations have shown propagation of 3-min slow magnetoacoustic waves (SMAWs) along fan loops from the solar photosphere to corona. In this work, we investigate the role of area divergence and frequencies on the damping of SMAWs propagating from the photosphere to the corona along several fan loops rooted in the sunspot umbra. We study the Fourier power spectra of oscillations along fan loops at each atmospheric height which showed significant enhancements in 1--2 min, 2.3--3.6 min and 4.2--6 min period bands. Amplitude of intensity oscillations in different period bands and heights are extracted after normalizing the filtered light curves with low-frequency background. We find damping of SMAW energy flux propagating along the fan loop 6 with damping lengths ~170 km and ~208 km for 1.5-min and 3-min period bands. We also show the decay of total wave energy content with height after incorporating area divergence effect, and present actual damping of SMAWs from photosphere to corona. Actual damping lengths in this case increases to ~172 km and ~303 km for 1.5-min and 3-min period bands. All the fan loops show such increase in actual damping lengths, and thus highlight the importance of area divergence effect. Results also show some frequency-dependent damping of SMAW energy fluxes with height where high-frequency waves are damped faster than low-frequency waves.