Effect of suppressed excitation on the amplitude distribution of 5-min oscillations in sunspots

TL;DR

This study combines 3D simulations and observational data to show that suppressed excitation sources in sunspots significantly reduce oscillation amplitudes, impacting sunspot seismology interpretations.

Contribution

It demonstrates through simulations and observations that suppression of excitation sources accounts for a large part of amplitude reduction in sunspots.

Findings

Oscillation amplitude in sunspots is 2-4 times lower due to suppressed sources.

Observed amplitude ratio inside vs. outside sunspots is approximately 3-4.

Suppressed excitation sources contribute at least 50% to amplitude reduction.

Abstract

Five-minute oscillations on the Sun (acoustic and surface gravity waves) are excited by subsurface turbulent convection. However, in sunspots the excitation is suppressed because strong magnetic field inhibits convection. We use 3D simulations to investigate how the suppression of excitation sources affects the distribution of the oscillation power in sunspot regions. The amplitude of random acoustic sources was reduced in circular-shaped regions to simulate the suppression in sunspots. The simulation results show that the amplitude of the oscillations can be approximately 2-4 times lower in the sunspot regions in comparison to the quiet Sun, just because of the suppressed sources. Using SOHO/MDI data we measured the amplitude ratio for the same frequency bands outside and inside sunspots, and found that this ratio is approximately 3-4. Hence, the absence of excitation sources inside sunspots makes a significant contribution (about 50% or higher) to the observed amplitude ratio and must be taken into account in sunspot seismology.