The solar radio flux at 2800 MHz (F10.7) and the sunspot number (SSN) are excellent indicators of solar activity. Data from 1986 to 2016 have been used to investigate long-term and mid-term periodicities of the F10.7 solar radio flux, the sunspot number, and galactic cosmic rays (GCRs) intensity, mainly from Oulu and Moscow, using fast Fourier Transform and Morlet wavelet techniques. The ≈ 148 days period, among other periods, is the one seen prominently in SSN, F10.7, and GCRs throughout Solar Cycles 22 to 24. This period could be the third harmonic of ≈ 1.24 years, i.e. ≈ 444 days period. The period of ≈ 1.24 years, found in SSN, F10.7 flux, and GCRs, is ascribed to the rotation of the convective envelope within the Sun during these cycles. Another period found significantly present in F10.7, SSN, and GCRs, is the Quasi-Biennial Oscillation (QBO), with a period of ≈ 1.94 years. The QBO amplitudes are found to vary significantly from one solar cycle to the other, with a minimum during Solar Cycle 24. The decreasing QBO amplitudes during Solar Cycle 24 in all three datasets are well correlated with the QBOs found in the Earth’s atmosphere-ionosphere system reported elsewhere.
Solar activity Sunspot number F10.7 radio flux Galactic cosmic rays
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The authors are grateful to the anonymous referee for valuable comments and suggestions which helped them to improve the paper. PRS gratefully acknowledges Prof. Abhay Kumar Singh, Department of Physics, Banaras Hindu University, Varanasi, India, for valuable suggestions. The authors are thankful to the Royal Observatory of Belgium for the SSN and NASA for F10.7 flux and cosmic ray intensity data at the neutron monitoring stations of Oulu and Moscow.
Disclosure of Potential Conflicts of Interest
The authors declare that there are no conflicts of interest.