Poloidal field at the northern pole (a), bottom toroidal field B_t at 15° latitude (b), and magnetic energy (c) in ascending phase of a magnetic cycle computed with perturbation in the α-effect imposed in a range of time between 0 yr and 2 yr. The full line shows the reference case of not varied α, the dashed line indicates the reversed sign of α, and the dash-dotted line shows the α increased bya factor of 3.