New paper shows 20th century solar activity was at highest levels of past 9,400 years

A new paper published in Astronomy & Astrophysics finds that solar activity may be influenced by gravitational torque from the orbital configuration of the planets. In addition, the authors show that solar activity during the 20th century was at the highest levels of the past 9,400 years.

Top graph shows solar activity in the 20th century was at the highest levels of the past 9,400 years. Time in years before the present shown on horizontal axis.

A&A 548, A88 (2012)

Is there a planetary influence on solar activity?

J. A. Abreu^1,2, J. Beer², A. Ferriz-Mas^3,4, K. G. McCracken⁵ and F. Steinhilber²

¹ ETH Zürich Institut für Geophysik, 8092 Zürich, Switzerland
e-mail: jose.abreu@erdw.ethz.ch
² Eawag, Swiss Federal Institute of Aquatic Science and Technology, Postfach 611, 8600 Dübendorf, Switzerland
³ Departamento the Física Aplicada, Universidade de Vigo, Spain
⁴ Instituto de Astrofísica de Andalucía (IAA/CSIC), Granada, Spain
⁵ University of Maryland, USA 

Received: 12 July 2012
Accepted: 24 September 2012

Abstract

Context. Understanding the Sun’s magnetic activity is important because of its impact on the Earth’s environment. Direct observations of the sunspots since 1610 reveal an irregular activity cycle with an average period of about 11 years, which is modulated on longer timescales. Proxies of solar activity such as ¹⁴C and ¹⁰Be show consistently longer cycles with well-defined periodicities and varying amplitudes. Current models of solar activity assume that the origin and modulation of solar activity lie within the Sun itself; however, correlations between direct solar activity indices and planetary configurations have been reported on many occasions. Since no successful physical mechanism was suggested to explain these correlations, the possible link between planetary motion and solar activity has been largely ignored.

Aims. While energy considerations clearly show that the planets cannot be the direct cause of the solar activity, it remains an open question whether the planets can perturb the operation of the solar dynamo. Here we use a 9400 year solar activity reconstruction derived from cosmogenic radionuclides to test this hypothesis.

Methods. We developed a simple physical model for describing the time-dependent torque exerted by the planets on a non-spherical tachocline and compared the corresponding power spectrum with that of the reconstructed solar activity record.

Results. We find an excellent agreement between the long-term cycles in proxies of solar activity and the periodicities in the planetary torque and also that some periodicities remain phase-locked over 9400 years.

Conclusions. Based on these observations we put forward the idea that the long-term solar magnetic activity is modulated by planetary effects. If correct, our hypothesis has important implications for solar physics and the solar-terrestrial connection.