Chromospheric Sunspot Oscillations in H-alpha and Ca II 8542A

TL;DR

This study investigates chromospheric oscillations in a sunspot using high-resolution spectroscopy, revealing frequency variations and their relation to magnetic field properties.

Contribution

It provides new insights into the spatial and frequency-dependent behavior of sunspot oscillations in H-alpha and Ca II lines, using advanced spectral analysis techniques.

Findings

High-frequency oscillations are enhanced inside the sunspot umbra.

Peak oscillation frequency decreases outward from the umbra.

Oscillation power correlates with magnetic field strength and inclination.

Abstract

We study chromospheric oscillations including umbral flashes and running penumbral waves in a sunspot of active region (AR) using scanning spectroscopy in H-alpha and Ca II 8542A, with the Fast Imaging Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at Big Bear Solar Observatory. A bisector method is applied to spectral observations to construct chromospheric Doppler velocity maps. Temporal sequence analysis of these shows enhanced high-frequency oscillations inside the sunspot umbra in both lines. Their peak frequency gradually decreases outward from the umbra. The oscillation power is found to be associated with magnetic-field strength and inclination, with different relationships in different frequency bands.