A secondary polar zone of solar prominences

Abstract

The polar prominences are concentrated in a zone, which in the period between sunspot minimum and maximum is shifted from about 45° heliographic latitude towards the pole. Cycle No. 20 has shown an anomaly never observed before, as on the northern hemisphere two zones of polar prominences were formed, the second zone following the first one at an interval of 2.5 yrs. The activity in the polar zone is closely connected with that in the main zone. This connection is much tighter than for instance the one between the northern and the southern hemisphere. We therefore investigated whether the anomalous appearance of a second polar zone might be related to a corresponding anomaly in the main zone. Such an irregularity exists in the latitude variation in the main zone. Such a irregularity exists in the latitude variation of the sunspots. After a regular decrease in heliographic latitude up to mid-1969, the northern sunspot zone suddenly shifted by 2.5° towards higher latitudes in the second half of 1969. This jump of the spot zone coincides with the appearance of the secondary polar zone of prominences.