Solar Toroidal Field Evolution Spanning Four Sunspot Cycles Seen By WSO, SOHO/MDI, and SDO/HMI

Forty-four years of Wilcox Solar Observatory (WSO), fourteen years of Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO), and eleven years of Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) magnetogram data have been studied to determine the east-west inclination, the toroidal component of the magnetic field. Maps of the east-west zonal averaged inclination produced by this study shows that each toroidal field cycle begins at around the same time at high latitudes in the Northern and Southern Hemispheres, and ends at the equator. Observation of these maps also show that each instance of a dominant toroidal field direction starts at high latitudes near sunspot maximum and is still visible near the equator well past the minimum of its cycle, indicating that the toroidal field cycle spans approximately 2 sunspot cycles. This supports earlier reports of the extended magnetic cycles.