POSTMODERN VIEW OF M-REGIONS

The discovery of coronal holes in the early 1970s was heralded as the discovery of the mysterious M-regions responsible for recurrent geomag netic activity. High-speed flow from the holes, sweeping past Earth on successive solar rotations, was directly correlated with sustained in creases in activity indices. We argue that this view of M-regions as c oronal holes is incomplete because it ignores work dating from the 196 0s demonstrating that peak recurrent activity coincides with passage o f corotating interaction regions between high- and low-speed flows. Th us, in an important way, M-regions include the boundary between corona l holes and coronal streamers, since streamers supply the slowest flow s. In addition, we suggest that coronal mass ejections propagating thr ough the streamer belt can contribute to the peak intensities of recur rent storms. Finally, we demonstrate that both peak recurrent activity and the following sustained activity that correlates with the high-sp eed flows are controlled by the Russell-McPherron effect: They are pro minent only when the azimuthal component of the Parker spiral field pr ojects a southward component in Earth's tilted dipole frame.