The sunspot cycle variations of the neutral line on the source surface

Abstract

We refine the earlier presentation method of the sunspot cycle variations of the neutral line on the source surface by introducing the view longitude. It is shown that the neutral line seen from the view longitude and the equivalent dipole (determined by Hoeksema, 1984) showed a trend of rotation throughout the sunspot cycle. However, the surface bounded by the neutral line is generally far from a circle. In fact, our combined presentation of both the equivalent dipole and the neutral line indicates graphically that such a simple description of the rotating (equivalent) dipole may be misleading. The concept of an inclined dipole with respect to the rotation axis may also be misleading.