Lifetimes and Rotation within the Solar Mean Magnetic Field

TL;DR

This study analyzes high-cadence solar magnetic field data over 20 years to measure the lifetime and rotation period of the rotationally-modulated component, linking it to magnetic flux concentrations and active regions.

Contribution

First measurement of the lifetime and rotation period of the RM component of the SMMF using high-cadence data, revealing its connection to magnetic flux concentrations.

Findings

Sidereal rotation period of RM component: 25.23 days

RM component lifetime: 139.6 days

Artefact identified as power aliasing in the spectrum

Abstract

We have used very high-cadence (sub-minute) observations of the solar mean magnetic field (SMMF) from the Birmingham Solar Oscillations Network (BiSON) to investigate the morphology of the SMMF. The observations span a period from 1992--2012, and the high-cadence observations allowed the exploration of the power spectrum up to frequencies in the mHz range. The power spectrum contains several broad peaks from a rotationally-modulated (RM) component, whose linewidths allowed us to measure, for the first time, the lifetime of the RM source. There is an additional broadband, background component in the power spectrum which we have shown is an artefact of power aliasing due to the low fill of the data. The sidereal rotation period of the RM component was measured as $25.23 \pm 0.11$ days and suggests that the signal is sensitive to a time-averaged latitude of $\sim 12^{\circ}$. We have also shown the RM lifetime to be $139.6 \pm 18.5$ days. This provides evidence to suggest the RM component of the SMMF is connected to magnetic flux concentrations (MFCs) and active regions (ARs) of magnetic flux, based both on its lifetime and location on the solar disc.