Back to Volume
Paper: Are We Entering a Period of Reduced Activity or a Grand Minima State?
Volume: 478, Fifty Years of Seismology of the Sun and Stars
Page: 167
Authors: Simoniello, R.; Jain, K.; Tripathy, S. C.; Baldner, C. S.; Turck-Chièze, S.; Hill, F.
Abstract: Solar cycle 23 has been characterized by an unpredicted deepest minimum in nearly a century, and solar cycle 24 has turned out to be 20% less strong than the previous cycle, against expectations. Are the current solar dynamics indicative that we might enter a period of reduced activity or even a Grand Minima state? To answer this question, we investigated the properties of the cyclic behavior of solar magnetic activity, characterized by the 11- and 2-year periodicity, the latter also known as the quasi-biennial periodicity (QBP). Recently it has been shown that the QBP signal might be the cycle period related to the quadrupolar component of the magnetic dynamo configuration. Observationally and theoretically, it has been shown that this component might play a key role over period of reduced activity by inducing a strong North–South asymmetry. We, therefore, wonder if the QBP signatures might be used as a precursor of solar magnetic activity. To this aim we used 17 years of Global Oscillation Network Group (GONG) observations to investigate the signatures and properties of the QBP in the dipolar and quadrupolar component of p-mode frequency shifts and in the even-order splitting coefficients of spherical degree ℓ = 0 – 120, as the latter are related to the magnetic field strength and oblateness. The observational findings seem to indicate that the QBP signal strength has been particularly strong over the ascending phase of solar cycle 23, but suddenly in 2003 became weaker and has remained weak over the ascending phase of solar cycle 24. We argue that the QBP, since 2003, suggested a week solar cycle 24 compared to cycle 23.
Back to Volume