Abstract
In this study, we used the flare index (FI) data taken from Kandilli Observatory for the period of 2009–2020. The data sets are analyzed in three categories as Northern Hemisphere, Southern Hemisphere, and total FI data sets. Total FI data set is obtained from the sum of Northern and Southern Hemispheric values. In this study, the periodic variations of abovementioned three categories FI data sets were investigated by using the MTM and Morlet wavelet analysis methods. The wavelet coherence (XWT) and cross wavelet (WTC) analysis methods were also performed between these data sets. As a result of our analysis, the following results were found: (1) long- and short-term periodicities ( 2048 ± 512 day and periodicities smaller than 62 days) exist in all data sets without any exception at least with 95 % confidence level; (2) all periodic variations were detected maximum during the solar cycle, while during the minima, no meaningful period is detected; (3) some periodicities have data preference that about 150 days Rieger period appears only in the whole data set and 682-, 204-, and 76.6-day periods appear only in the Northern Hemisphere data sets; (4) During the Solar Cycle 24, more flare activity is seen at the Southern Hemisphere, so the whole disk data periodicities are dominated by this hemisphere; (5) in general, there is a phase mixing between Northern and Southern Hemisphere FI data, except about 1024-day periodicity, and the best phase coherency is obtained between the Southern Hemisphere and total flare index data sets; (6) in case of the Northern and Southern Hemisphere FI data sets, there is no significant correlation between two continuous wavelet transforms, but the strongest correlation is obtained for the total FI and Southern Hemisphere data sets.
Highlights
Solar flares (SFs) are one of the most intense eruptions observed on the Sun. ey can occur in the corona above active regions, sunspots, magnetic network boundaries, network, etc. [1,2,3]
As shown in this figure, Northern and Southern Hemisphere flare index (FI) data show some differences that the Northern Hemisphere is dominant during the first half of the cycle, while the Southern Hemisphere data become dominant during the second half of the cycle
From these figures (Figures 2–4) and from Table 1, we obtained the following results: (i) 2048 ± 512 days (5.6 years) and the periodicities smaller than 62 days exist in all data sets without any exception at least with 95% confidence level; (ii) as shown in Table 1, all periods appear during the solar cycle maximum; (iii) about 150 days Rieger period appears only in the whole data set, while 682, 204, and 76.6-day periods appear only in the Northern Hemisphere data sets; (iv) in general periodicities obtained from the Southern Hemisphere FI data are all appear in the whole disk data, we may argue that the Southern Hemisphere flare activity was dominant during the Solar Cycle 24
Summary
Solar flares (SFs) are one of the most intense eruptions observed on the Sun. ey can occur in the corona above active regions, sunspots, magnetic network boundaries, network, etc. [1,2,3]. Solar flares (SFs) are one of the most intense eruptions observed on the Sun. ey can occur in the corona above active regions, sunspots, magnetic network boundaries, network, etc. Erefore, the regular observations of solar flares have very big importance, especially from the point of space weather and Sun-Earth interactions. E periodic variation of solar activity indices is investigated by using different indicators such as sunspot number and area, TSI, 10.7 cm solar radio flux, and flare index [5, 10,11,12].
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