Magnetohydrodynamic Instabilities of Double Magnetic Bands in a Shallow-water Tachocline Model. II. Teleconnection Between High- and Low-latitude Bands and Across Equator

Abstract 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 the 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, and hence the earlier the cycle starts declining.