Properties of high-degree oscillation modes of the Sun observed with Hinode/SOT

TL;DR

This study investigates high-degree solar oscillations observed in different atmospheric layers using Hinode/SOT, revealing frequency shifts and phase behaviors that inform models of wave excitation and atmospheric dynamics.

Contribution

It provides new insights into the properties of high-degree solar oscillations across atmospheric layers and compares observations with a simple theoretical model including correlated noise effects.

Findings

Significant frequency shifts between Ca II H and G-band spectra above the acoustic cut-off.

Phase peaks associated with p-mode oscillations and increased phase with frequency.

Correlated noise levels differ between Ca II H and G-band data, affecting observed properties.

Abstract

Aims. With the Solar Optical Telescope on Hinode, we investigate the basic properties of high-degree solar oscillations observed at two levels in the solar atmosphere, in the G-band (formed in the photosphere) and in the Ca II H line (chromospheric emission). Methods. We analyzed the data by calculating the individual power spectra as well as the cross-spectral properties, i.e., coherence and phase shift. The observational properties are compared with a simple theoretical model, which includes the effects of correlated noise. Results. The results reveal significant frequency shifts between the Ca II H and G-band spectra, in particular above the acoustic cut-off frequency for pseudo-modes. The cross-spectrum phase shows peaks associated with the acoustic oscillation (p-mode) lines, and begins to increase with frequency around the acoustic cut-off. However, we find no phase shift for the (surface gravity wave) f-mode. The observed properties for the p-modes are qualitatively reproduced in a simple model with a correlated background if the correlated noise level in the Ca II H data is higher than in the G-band data. These results suggest that multi-wavelength observations of solar oscillations, in combination with the traditional intensity-velocity observations, may help to determine the level of the correlated background noise and to determine the type of wave excitation sources on the Sun.