Unexpected frequency of horizontal oscillations of magnetic structures in the solar photosphere

TL;DR

This study reveals an unexpected dominant oscillation frequency of about 5 mHz in solar photospheric magnetic structures, differing from the typical 3 mHz, suggesting a different underlying driver of these oscillations.

Contribution

It uncovers a novel dominant frequency in photospheric magnetic elements, challenging previous assumptions about solar oscillations and their origins.

Findings

Dominant oscillation frequency around 5 mHz in magnetic structures

Contrasts with the typical 3 mHz frequency in the solar photosphere

Suggests a different oscillatory driver than previously thought

Abstract

It is well known that the dominant frequency of oscillations in the solar photosphere is $\approx$3 mHz, which is the result of global resonant modes pertaining to the whole stellar structure. However, analyses of the horizontal motions of nearly 1 million photospheric magnetic elements spanning the entirety of solar cycle 24 have revealed an unexpected dominant frequency, $\approx$5 mHz, a frequency typically synonymous with the chromosphere. Given the distinctly different physical properties of the magnetic elements examined in our statistical sample, when compared to largely quiescent solar plasma where $\approx$3 mHz frequencies are omnipresent, we argue that the dominant $\approx$5 mHz frequency is not caused by the buffeting of magnetic elements, but instead is due to the nature of the underlying oscillatory driver itself. This novel result was obtained by exploiting the unmatched spatial and temporal coverage of magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) on board NASA's Solar Dynamics Observatory (SDO). Our findings provide a timely avenue for future exploration of the magnetic connectivity between sub-photospheric, photospheric, and chromospheric layers of the Sun's dynamic atmosphere.