Formation of a Switchback During the Rising Phase of Solar Cycle 21

The customary notion that high-latitude filaments arise from magnetic flux originating in the active-region belts finds its modern expression in numerical models that generate filament channels from flux patterns migrating from active latitudes to the polar caps. Polarity inversions underlying high-latitude filament channels are swept into distinct patterns called `switchbacks' under the joint influence of differential rotation, supergranular diffusion, and meridional flow. The numerical model of Mackay and van Ballegooijen (2001) predicts a heretofore unsuspected solar-cycle dependence to the hemispheric pattern of filament magnetic fields. Observations presented here of a switchback formed early in cycle 21 confirm some key aspects of their model. In this remarkable example the flux diffusing out of the source region migrates to the opposite side of the Sun before it encounters another active region with which to create the quadrupolar field configuration wherein a return arm forms to complete the switchback.