Monday

As seen in multiple solar activity proxies, Cycle 24 was considerably weaker than preceding cycles, which raises the question as to how a weakened solar cycle may affect the presence or properties of the quasi-biennial oscillation (QBO). Through investigating the cycle dependency of the QBO we can gain a better understanding of the mechanism that generates it, and in turn further confine properties of the solar dynamo. We use helioseismic techniques to examine the QBO through measuring the frequency shifts of global p-modes over both solar cycles, where the modes are sorted by frequency and the depth to which they travel in the solar interior.

We use Empirical Mode Decomposition (EMD) to extract statistically significant oscillations in the frequency variations of the intermediate harmonic degree modes from the from the Global Oscillations Network Group (GONG) and MDI/HMI (Michelson Doppler Imager, Helioseismic & Magnetic Imager). We also employ EMD on solar activity proxies, the MgII Index and the 10.7 cm radio flux. We see evidence of the QBO in helioseismic data above a 95% confidence level with average periods ranging from approximately 400-800 days across both cycles, although the presence of the QBO is reduced in Cycle 24. The number of detections of QBO-like signals showed no dependence on the p-modes frequency, or on the modes lower turning point where data was available (0.22-0.95 solar radii). We therefore propose that the magnetic field generating the QBO is anchored above 0.95 solar radii. We see no statistically significant evidence of the QBO in solar activity proxy data and we conclude that the abundance of detections of the QBO is cycle dependant.