Active Latitude Oscillations Observed on the Sun
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We investigate periodicities in the mean heliographic latitudes of sunspot groups, called active latitudes, for the past six complete solar cycles (1945 – 2008). For this purpose, the multitaper method and Morlet wavelet analysis were used. We found that solar rotation periodicities (26 – 38 days) are present in active latitudes of both hemispheres for all the investigated cycles (18 to 23). Both in the northern and southern hemispheres, active latitudes drifted toward the equator from the beginning to the end of each cycle and followed an oscillating path. These motions are well described by a second-order polynomial. There are no meaningful periods of between 55 and about 300 days in either hemisphere for all cycles. A periodicity of 300 to 370 days appears in both hemispheres for Cycle 23, in the northern hemisphere for Cycle 20, and in the southern hemisphere for Cycle 18.
KeywordsSun Sunspots Heliographic latitude Periodicity
The sunspot group data used in this study were retrieved from the National Aeronautics and Space Administration (NASA) online data archives. The wavelet software was provided by C. Torrence and G. Compo and is available at http://paos.colorado.edu/research/wavelets/ . This study was supported by the Scientific and Technical Council of Turkey by the Project of 115F031. V. Yurchyshyn acknowledges support from the AFOSR Award FA9550-15-1-0322, the NSF AGS-1146896 grant and the Korea Astronomy and Space Science Institute. F. Clette would like to acknowledge financial support from the Belgian Solar-Terrestrial Center of Excellence (STCE; http://www.stce.be ). J.-P. Rozelot would like to thank the International Space Science Institute in Bern (CH) for its support of this study.