The quasi-biennial periodicity as a window on the solar magnetic dynamo configuration

TL;DR

This study investigates the 2-year solar magnetic activity cycle by analyzing acoustic mode frequency shifts, revealing subsurface origins and latitudinal variations, and suggests it results from magnetic dynamo interactions.

Contribution

It provides new insights into the subsurface origins and latitudinal dependence of the quasi-biennial periodicity using 17 years of GONG data, linking it to dynamo magnetic configurations.

Findings

Frequency shifts originate in subsurface layers.

Shift amplitude increases towards equator and solar maximum.

QBP causes weaker and slower frequency shifts than the 11-year cycle.

Abstract

Manifestations of the solar magnetic activity through periodicities of about 11 and 2 years are now clearly seen in all solar activity indices.In this paper, we add information about the mechanism driving the 2 year period by studying the time and latitudinal properties of acoustic modes that are sensitive probes of the subsurface layers. We use almost 17 years of high quality resolved data provided by the Global Oscillation Network Group (GONG) to investigate the solar cycle changes in p-mode frequencies for spherical degrees l from 0 to 120 and 1.6 mHz < nu < 3.5 mHz. For both periodic components of solar activity, we locate the origin of the frequency shift in the subsurface layers and put in evidence for a sudden enhancement in amplitude just in the last few hundred kilometers. We also show that, in both cases, the size of the shift increases towards equatorial latitudes and from minimum to maximum of solar activity, but, in agreement with previous findings,the quasi-biennial periodicity (QBP) causes a weaker shift in mode frequencies and a slower enhancement than the one caused by the 11 year cycle. We compare our observational findings with the features predicted by different models that try to explain the origin of this QBP and conclude that the observed propertiescould result from the beating between a dipole and quadrupole magnetic configuration of the dynamo.