The Astrophysical Journal: The 'extended solar cycle' indicates that there are two deeply seated toroidal magnetic field bands in each hemisphere. Both bands migrate equatorward as a sunspot cycle progresses. Here we examine the consequences of global MHD instability of this migrating double-band system in tachocline on the latitudinal structure of unstable modes, which are essentially MHD Rossby waves. We find that latitude-location, latitude-separation, and amplitude of the bands strongly influence the latitudinal structure and growth rates of the unstable modes, of both symmetries about the equator. These properties can lead to 'teleconnections' between low- and high-latitudes in each hemisphere and across the equator. High-latitude bands can destabilize low-latitude bands that would otherwise be stable. Stronger high-latitude bands lead to strong interactions between low and high latitude in each hemisphere, but inhibit cross-equatorial band-interaction. Strong cross-equatorial interactions of modes can synchronize cycle minima in North and South. Symmetric and antisymmetric modes of similar amplitudes can lead to substantial asymmetries between North and South. As a solar cycle progresses, excited MHD Rossby waves go through a sequence of changes in latitude structure and growth rate while maintaining strong links in latitude. These changes and links are theoretical evidence of teleconnections between widely separated latitudes and longitudes in the Sun, which may explain many of the evolving surface magnetic patterns observed as a solar cycle progresses. The wider the separation between high- and low-latitude bands, the earlier the cross-equatorial teleconnection starts in a cycle, hence the earlier the cycle starts declining.
Middle panel: Snapshots of flows (white arrow vectors) and magnetic fields (black arrow vectors) overlaid on the deformable top-surface of the shell (color-map) in latitude–longitude planform for the antisymmetric m=2 (left) and symmetric m = 1 (right) modes, respectively. Field strengths and band locations are noted in the figure at the center. Equatorial region is enlarged to display cross-equatorial communication via flows (top panels on extreme left and extreme right) and fields (bottom panels on extreme left and extreme right). Note that the velocity vectors are also plotted in black arrows instead of white arrows for better visibility. In the right-most panels, green is the prominent color because green implies no bulges or depressions, which is the case near the equator for the symmetric mode.