Seismic comparison of the 11 and 2 yr cycle signatures in the Sun

TL;DR

This study analyzes 15 years of solar oscillation data to compare the 11-year and 2-year solar activity cycles, revealing their subsurface origins and differences in their effects on p-mode frequencies.

Contribution

It provides new insights into the subsurface origins of the 11-year and 2-year solar cycles and their distinct signatures in p-mode frequency shifts.

Findings

Frequency shifts originate in subsurface layers with increased amplitude near the surface.

The 2-year cycle causes a weaker and slower frequency shift compared to the 11-year cycle.

Frequency shift magnitude increases towards the equator and from solar minimum to maximum.

Abstract

The solar magnetic activity consists of two periodic components: the main cycle with a period of 11 yr and a shorter cycle with a period of ~2 yrs. The origin of this second periodicity is still not well understood. We use almost 15 yrs of long high quality resolved data provided by the Global Oscillation Network Group (GONG) to investigate the solar cycle changes in p-mode frequency with spherical degree l=0-120 and in the range 1600muHz < nu < 3500 muHz. For both periodic components of solar magnetic activity our findings locate the origin of the frequency shift in the subsurface layers with a sudden enhancement in the amplitude of the shift in the last few hundred kilometers. We also show that the size of the shift increases towards equatorial latitudes and from minimum to maximum of solar activity. On the other hand, the signatures of the 2 yr cycle differ from the one of the 11 yr cycle in the magnitude of the shift, as the 2 yr cycle causes a weaker shift in mode frequencies and a slower enhancement in the last few hundreds kilometers. Based on these findings we speculate that a possible physical mechanism behind the quasi biennial periodicity (QBP) could be the beating between different dynamo modes (dipole and quadrupole mode)