Oscillations in Secondary to Primary Polar Crown Polarity Inversion Lines around Solar Maximum over Five Solar Cycles

Abstract:

We undertake a five solar-cycle (SC19-23, Dec. 1954 – Aug. 2009) study of oscillations in the high-latitude polarity inversion lines (PILs) using the recently digitized McIntosh Archive of solar synoptic maps. We look at the evolution of the primary PIL, which is the nearly continuous polar crown filament (PCF) line bounding the polar coronal hole (CH). The secondary PIL consists of neutral line segments equatorward of the primary PIL, and it becomes a nearly continuous PCF line at the end of the rush to the poles before solar maximum when the polar polarity reverses with the primary PIL disappearing, and the secondary PIL becomes the primary PIL with the new polarity. This new primary PIL achieves a maximum poleward latitude of ~+/-57 degrees, and then relaxes equatorward in oscillations of 2-5 degrees of latitude with periods between ~10-35 Carrington Rotations (CRs). In 2005, we saw equatorward drops in the PIL and CH boundaries that started in the southern hemisphere pole and ended in the north pole, with ~35CR wave periods before and ~20CR after the break. The oscillations and breaks are new aspects of the general evolutionary patterns of surface features that need to be accounted for by interior dynamo models.