Low-degree solar rotational splitting from 45 years of BiSON observations

TL;DR

This paper analyzes 45 years of Sun-as-a-star observations to measure low-degree solar rotational splitting, revealing a consistent frequency-independent value after accounting for biases and uncertainties.

Contribution

It provides a new long-term analysis of solar rotational splitting using a Markov Chain Monte Carlo method on extensive observational data.

Findings

Estimated splitting value of 400 nHz after bias correction

Formal uncertainties are underestimated by about 30%

Bias increases at frequencies above 2200 microHz

Abstract

We present solar low-degree rotational splitting values based on a new analysis of Sun-as-a-star observations from the Birmingham Solar Oscillations Network, covering a 16,425-day period from 1976 December 31--2021 December 20 with a duty cycle of 57 per cent. The splitting values are estimated from the power spectrum using a Markov Chain Monte Carlo sampling method, and we also present for comparison the results from an analysis of 100 realizations of synthetic data with the same resolution and gap structure. Comparison of the scatter in the results from the synthetic realizations with their estimated uncertainties suggests that for this data set the formal uncertainty estimates are about 30 per cent too small. An upward bias in the splittings at frequencies above 2200 microHz, where the components are not fully resolved, is seen in both the observed and synthetic data. When this bias is taken into account our results are consistent with a frequency-independent synodic rotational splitting value of 400 nHz.