Abnormal oscillation modes in a waning light bridge

TL;DR

This study investigates oscillation patterns in a sunspot's light bridge using SDO/AIA data, revealing persistent five-minute and sub-minute oscillations with asymmetric spatial distributions and jet activities, leading to a new magnetic field model.

Contribution

The paper introduces a novel model of twisted magnetic fields in light bridges based on detailed oscillation and jet activity analysis.

Findings

Five-minute oscillations follow the bridge spine

Sub-minute oscillations overlap with bridge flanks

Asymmetry in oscillation patterns and jet activities between flanks

Abstract

A sunspot acts as a waveguide in response to the dynamics of the solar interior; the trapped waves and oscillations could reveal its thermal and magnetic structures. We study the oscillations in a sunspot intruded by a light bridge, the details of the oscillations could reveal the fine structure of the magnetic topology. We use the Solar Dynamics Observatory/Atmospheric Imaging Assembly data to analyse the oscillations in the emission intensity of light bridge plasma at different temperatures and investigate their spatial distributions. The extreme ultraviolet emission intensity exhibits two persistent oscillations at five-minute and sub-minute ranges. The spatial distribution of the five-minute oscillation follows the spine of the bridge; whereas the sub-minute oscillations overlap with two flanks of the bridge. Moreover, the sub-minute oscillations are highly correlated in spatial domain, however, the oscillations at the eastern and western flanks are asymmetric with regard to the lag time. In the meanwhile, jet-like activities are only found at the eastern flank. Asymmetries in forms of oscillatory pattern and jet-like activities \textbf{are} found between two flanks of a granular light bridge. Based on our study and recent findings, we propose a new model of twisted magnetic field for a light bridge and its dynamic interactions with the magnetic field of a sunspot.