Strength and phase of the solar dynamo during the last 12 cycles

We use the nn index of geomagnetic activity recorded for 1.30 years to stud y the strength and phase properties of the solar dynamo. We split the month ly averaged cta into two pacts: one part proportional to the sunspot number and the other part proportional to the residual. We argue that the first p art is a prosy for the solar dynamo's large-scale mean toroidal magnetic fi eld. The residual has the same periodicity as the sunspot cycle and has clo sely related amplitude, but: is shifted in phase. WE relate this residual t o the poloidal field generated from the toroidal field in the dynamo proces s. The changes in both components demonstrate that there was a long-term tr end in the strength and relative phases of the toroidal and poloidal compon ents of the mean-field dynamo. The changes in the relative phase of the tor oidal and poloidal fields suggest that the distributions of the differentia l rotation and helicity within the Sun's convection zone have changed over timescales of 50 years.