Abstract
We study the longitudinal distribution of sunspot activity in 1917–1995 using vector sums of sunspot areas. The vector sum of sunspots of one solar rotation gives a total vector whose amplitude characterizes the size of longitudinal asymmetry and whose phase describes the location of the momentarily dominating longitude. We find that when the phase distributions are calculated separately for the ascending phase and maximum (AM) on the one hand and for the declining phase and minimum (DM) on the other hand, they behave differently and depict broad maxima around roughly opposite longitudes. While the maximum of the phase distribution for the AM period is found around the Carrington longitude of 180°, the maximum for the DM period is at the longitude of about 0°. This difference can be seen in both solar hemispheres, but it is more pronounced in the southern hemisphere where the phase distribution has a particularly clear pattern. No other division of data into two intervals leads to similar systematic differences.
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Vernova, E., Mursula, K., Tyasto, M. et al. Long-term longitudinal asymmetries in sunspot activity: Difference between the ascending and descending phase of the solar cycle. Solar Physics 221, 151–165 (2004). https://doi.org/10.1023/B:SOLA.0000033367.32977.71
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DOI: https://doi.org/10.1023/B:SOLA.0000033367.32977.71