The average tilt angle of sunspot groups emerging throughout the solar cycle
determines the net magnetic flux crossing the equator, which is correlated with
the strength of the subsequent cycle. I suggest that a deep-seated, non-local
process can account for the observed cycle-dependent changes in the average
tilt angle. Motivated by helioseismic observations indicating cycle-scale
variations in the sound speed near the base of the convection zone, I
determined the effect of a thermally perturbed overshoot region on the
stability of flux tubes and on the tilt angles of emerging flux loops. I found
that 5-20 K of cooling is sufficient for emerging flux loops to reproduce the
reported amplitude of cycle-averaged tilt angle variations, suggesting that it
is a plausible effect responsible for the nonlinearity of the solar activity
cycle.Comment: 5 pages, 4 figures, 1 table - published on 26 October 201
