  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 midlatitudes 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.
