Temporal and Periodic Variations of the Solar Flare Index During the Last Four Solar Cycles and Their Association with Selected Geomagnetic-Activity Parameters

Document Type

Article

Publication Date

9-1-2022

Abstract

We studied the temporal and periodic variations of the monthly solar flare index (FI) and selected geomagnetic-activity parameters (Ap, Dst, Scalar B, and aa) measured during Solar Cycles 21 – 24 (from January 1, 1975 to December 31, 2020) and report the following findings: 1) all data sets except the FI peak values gradually decreased after 1992, while the FI peak values began their gradual decrease in 1982; 2) all data sets show double or multiple peaks during the maximum phase of solar cycles; 3) the FI shows meaningful correlations with the investigated geomagnetic-activity parameters; 4) the 11-year sunspot-cycle periodicity and periodicities lower than 3.9 months were observed in all data sets without exception; 5) the FI time series exhibits a unique period of 4.8 – 5.2 months that is not present in all the other indices, while geomagnetic aa, Ap, and Dst indices show a unique 6 – 6.1 months periodicity that does not appear in the scalar B and FI; 6) crosswavelet transform (XWT) spectra between FI and other parameters generally show phase mixing in the short (2 – 8 months) period range, while all parameters used in this study were found to be inphase and highly correlated with the 11-year solar-activity period. All these results show that the FI variations are one of the main drivers of the geomagnetic activity.

Identifier

85138117178 (Scopus)

Publication Title

Solar Physics

External Full Text Location

https://doi.org/10.1007/s11207-022-02049-7

e-ISSN

1573093X

ISSN

00380938

Issue

9

Volume

297

Grant

AGS-1954737

Fund Ref

National Science Foundation

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