A mechanism for the dependence of sunspot group tilt angles on cycle strength

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Işık, Emre
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Iop Publıshıng Ltd, Temple Circus, Temple Way, Bristol Bs1 6Be, England
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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.
Anahtar kelimeler
Sun: activity, Sun: interior, Sun: magnetic fields, Sunspots, Magnetic-Flux Tubes, Convection Zone, Solar-Cycle, Base, Sun, Intensification, Overshoot, Envelope, Models