Periodicities in the longitude distribution of sunspots

It is well known to the observer of sunspots that the spots seem not to be randomly distributed on the solar surface but rather occur at an increased rate at distances of 180° of each other on the same hemisphere while northern and southern hemispheres are independent. The following investigation - based on observational data of rotations No. 1457–1568 (1962–1970) shows four main results:

1. Northern and southern hemisphere behave independently.
2. Each hemisphere can be divided in longitude into sections of 45° so that successive sections alternatively show higher and lower spot occurrence. In other words: maximum spot occurrence is found in intervals of about 90° and 180°.
3. Second-order peaks can be found in intervals of 30° and multiples of it. The spot maxima explained above coincide with some of these second-order peaks.
4. Areas of minimal spot occurrence can be traced over a long period of time. These areas can be understood as the center of long-living magnetic areas along the borders of which we find the so-called ‘streets of prominences’ with its spots. This theory of Stanek (1971) explains the occurrence of prominences. Because of the steep magnetic gradient along these streets the theory is expected to hold true even for spots. This leads to a better understanding of the pattern already known and now being generalized to ‘streets of activity’.