Cycle dependency of a quasi-biennial variability in the solar interior

TL;DR

This study examines how the Quasi-Biennial Oscillation (QBO) in the solar interior varies with the solar cycle, revealing a reduced QBO presence in Cycle 24 and suggesting the magnetic field origin above 0.95 solar radii.

Contribution

It provides new insights into the solar cycle dependence of QBO and identifies the magnetic field region responsible for QBO in the solar interior.

Findings

QBO presence is reduced in Cycle 24 compared to Cycle 23.

QBO-related frequency shifts are not sensitive to p-mode depth or frequency.

Magnetic field responsible for QBO is likely anchored above 0.95 solar radii.

Abstract

We investigated the solar cycle dependency on the presence and periodicity of the Quasi-Biennial Oscillation (QBO). Using helioseismic techniques, we used solar oscillation frequencies from the Global Oscillations Network Group (GONG), Michelson Doppler Imager (MDI) and Helioseismic & Magnetic Imager (HMI) in the intermediate-degree range to investigate the frequency shifts over Cycles 23 and 24. We also examined two solar activity proxies, the F10.7 index and the MgII index, for the last four solar cycles to study the associated QBO. The analyses were performed using Empirical Mode Decomposition (EMD) and the Fast Fourier Transform (FFT). We found that the EMD analysis method is susceptible to detecting statistically significant Intrinsic Mode Functions (IMFs) with periodicities that are overtones of the length of the dataset under examination. Statistically significant periodicites, which were not due to overtones, were detected in the QBO range. We see a reduced presence of the QBO in Cycle 24 compared to Cycle 23. The presence of the QBO was not sensitive to the depth to which the p-mode travelled, nor the average frequency of the p-mode. The analysis further suggested that the magnetic field responsible for producing the QBO in frequency shifts of p-modes is anchored above approximately 0.95 solar radii.