We have analysed the observations of Solar Ca+K daily plage area for the period 1951-1977 to find evidence for the existence of short period (around 12–13 days) variation in the data. We divided the data in three groups—two corresponding to 10–20‡N and 10–20‡S latitude belts, and one corresponding to the total plage area—and used the power spectrum and autocorrelation techniques for the analysis. Both the techniques clearly show the 27-day periodicity due to solar rotation modulation in all the sets. A 12–13 day periodicity is seen in only 3, out of a total of 57 data sets when autocorrelation technique is used. A generally weak peak around 12–13 days is, however, seen in the power spectrum of all the data sets. The relative power in the 12–13 day peak is found to be significantly higher in those three data sets where the autocorrelation also shows this periodicity. On these two epochs the sunspot area distribution showed the existence of two distinct active longitudes separated by about 140–170 degrees. This seems to be the cause for the existence of a periodicity around 12–13 days in the autocorrelation and enhancement in the relative power of the 12–13 days peak in the power spectrum of these two epochs
Volume 42, 2021
Continuous Article Publishing mode
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.
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