Seismic comparison of the 11‐ and 2‐year cycle signatures in the Sun

Abstract

AbstractThe 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 yr. The origin of this second periodicity is still not well understood. We use almost 15 years of long high‐quality resolved data provided by the Global Oscillation Network Group (GONG) to investigate the solar cycle changes in p‐mode oscillations with spherical degree Ł = 0–120 and in the range of 1600 µHz ≤ ν ≤ 3500 µHz. 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 hundred 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) (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)