Table of Contents
ISRN Astronomy and Astrophysics
Volume 2011 (2011), Article ID 437838, 11 pages
Research Article

Why the Sunspot Cycle Is Double Peaked

Space and Solar-Terrestrial Research Institute, Bulgarian Academy of Sciences, 1000 Sofia, Bulgaria

Received 31 January 2011; Accepted 28 February 2011

Academic Editors: M. Ding and S. Jefferies

Copyright © 2011 K. Georgieva. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Many sunspot cycles are double peaked. In 1967, Gnevyshev suggested that actually all cycles have two peaks generated by different physical mechanisms, but sometimes the gap between them is too short for the maxima to be distinguished in indices of the total sunspot activity. Here, we show that indeed all cycles have two peaks easily identified in sunspot activity in different latitudinal bands. We study the double peaks in the last 12 sunspot cycles and show that they are manifestation of the two surges of toroidal field—the one generated from the poloidal field advected all the way on the surface to the poles, down to the tachocline and equatorward to sunspot latitudes, and another one generated from the poloidal field diffused at mid-latitudes from the surface to the tachocline and transformed there into toroidal field. The existence of these two surges of toroidal field is due to the relative magnitudes of the speed of the large-scale solar meridional circulation and the diffusivity in the solar convection zone which are estimated from geomagnetic data.