Observations of Sunspot Oscillations in G band and Ca II H line with Solar Optical Telescope on Hinode

TL;DR

This study uses high-resolution Hinode observations to analyze sunspot oscillations in G-band and Ca II H lines, revealing spatial variations and features like umbral flashes and a mysterious power suppression region.

Contribution

It provides detailed spatial analysis of sunspot oscillations in different spectral lines, highlighting new features such as the node-like power suppression in the umbra.

Findings

Umbral oscillatory power is suppressed in G-band.

Ca II H shows prominent umbral flashes peaking at 5.5 mHz.

A central power suppression region in the umbra remains unexplained.

Abstract

Exploiting high-resolution observations made by the Solar Optical Telescope onboard Hinode, we investigate the spatial distribution of power spectral density of oscillatory signal in and around NOAA active region 10935. The G-band data show that in the umbra the oscillatory power is suppressed in all frequency ranges. On the other hand, in Ca II H intensity maps oscillations in the umbra, so-called umbral flashes, are clearly seen with the power peaking around 5.5 mHz. The Ca II H power distribution shows the enhanced elements with the spatial scale of the umbral flashes over most of the umbra but there is a region with suppressed power at the center of the umbra. The origin and property of this node-like feature remain unexplained.