Oscillatory Response of the Solar Chromosphere to a Strong Downflow above a Sunspot

TL;DR

This study observes three-minute oscillations in the solar chromosphere triggered by a strong downflow event above a sunspot, revealing how impulsive flows can induce oscillatory behavior in the solar atmosphere.

Contribution

It provides observational evidence linking impulsive downflows to chromospheric oscillations, supporting theoretical models of sunspot dynamics.

Findings

Oscillations with 2 km/s amplitude observed after downflow

Oscillation period increased from 2.7 to 3.3 minutes

Transient brightening near downflow footpoint detected

Abstract

We report three-minute oscillations in the solar chromosphere driven by a strong downflow event in a sunspot. We used the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope and the Interface Region Imaging Spectrograph (IRIS). The strong downflow event is identified in the chromospheric and transition region lines above the sunspot umbra. After the event, oscillations occur at the same region. The amplitude of the Doppler velocity oscillations is 2 km/s, and gradually decreases with time. In addition, the period of the oscillations gradually increases from 2.7 minutes to 3.3 minutes. In the IRIS 1330 slit-jaw images, we identify a transient brightening near the footpoint of the downflow detected in the Ha+0.5A image. The characteristics of the downflowing material are consistent with those of sunspot plumes. Based on our findings, we suggest that the gravitationally stratified atmosphere came to oscillate with three minute period in response to the impulsive downflow event as was theoretically investigated by Chae & Goode(2015).