Latitude Distribution of Weak Photospheric Magnetic Fields in Solar Cycles 21−24

Variations of weak photospheric magnetic fields with periods on the order of the solar magnetic cycle have been studied. We used synoptic maps of the photospheric magnetic field for the period 1978−2016 (NSO Kitt Peak). To isolate the contribution of weak magnetic fields, the saturation threshold for the synoptic maps was set at 5 G. A time–latitude diagram was constructed from the converted synoptic maps. For further analysis, 18 magnetic field profiles were selected from the diagram. It was found that a 22-year variation in weak magnetic fields is present not only at high, but also at low latitudes. We show that at all latitudes, with the exception of ~26° and ~33° in the Northern Hemisphere and ~−26° in the Southern Hemisphere, weak magnetic fields change cyclically with an average period of 22.3 years. At high latitudes, the magnetic fields of the two hemispheres change approximately out of phase. In contrast, equatorial latitudes are in phase with the high latitude fields of the Northern Hemisphere and out of phase with the Southern Hemisphere. Thus, at low latitudes, the dominant role of the Northern Hemisphere becomes noticeable: the equatorial fields are in phase with the fields of the Northern Hemisphere at high latitudes. The phase of the 22-year variation changes gradually with latitude, but when the 22-year variation is disrupted, phase jumps occur. Before and after the disruption period, the 22-year variation develops in antiphase.