On 156-day quasi-periodicity of the solar indices

Heading: 
Akimov, LO, 1Belkina, IL
1Research Institute of Astronomy at V.N. Karazin Kharkiv National University, Kharkiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2011, 27(3):40-53
Start Page: Solar Physics
Language: Russian
Abstract: 

Some series of the daily so lar indices of the sunspot number W (1900—2008), of the solar flux F10.7 at 2800 MHz (1947— 2008) and numbers Nx for X-ray flares (1981—2008) are studied. The methods of the Fourier analysis and wavelet analysis are used to detect the 156-day quasi-periodicity, so-called the Rieger type periodicity, RTP. Statistically significant amplitude of RTP for the W index was observed near the solar maxima for most of the considered solar cycles, with the exception of the 14th, 15th and 23rd cycles. The largest power of the 156-day peak was observed during the declin ing phase of cycle 16, at the maximum of cycle 21 and during the increasing phase of cycles 20 and 23. The statistically significant RTP was also observed at the minima of cycles 17,18 and 19. We conclude that the RTP dependence on a solar cycle phase is unstable. The time dependence of the RTP for the index F10.7 obtained through the wavelet-analysis is almost identical to that for the index W, with the correlation coefficient between temporal behaviours of the RTP being equal to 0.95. The correlation coefficients between temporal behaviours of the RTP for the pairs of indices W-Nx and F10.7-Nx and equal 0.36 and 0.32, respectively. No time lags between the RTP beginnings for various indices are detected. Therefore, the 156-day quasi-periodicity involves almost simultaneously events occurring in active regions of the solar atmosphere at different heights. The assumed nature of the RTP is discussed.

Keywords: solar indices, sunspot