Significant short-term variations of ≈1.7, ≈2.4, ≈2.8, ≈3.3, ≈3.8 days periods are found when high resolution data (five minutes average) of interplanetary electric field (Ey), south ward component of magnetic field (Bz) and geomagnetic index (AE) is subjected to wavelet analysis. The fourth, fifth, sixth sub harmonics of ≈27-day period, and few other short-term periods are significantly reported by Singh and Badruddin (Astrophys. Space Sci. 359:60, 2015a; Solar Phys. 290:3071, 2015b and Solar Phys. 294:27, 2019) in cosmic ray intensity, geomagnetic activity index and various solar wind plasma and field parameters. The reported and observed periods ≈6.8 day, ≈5.5 day, ≈4.4 day, ≈3.9 day, ≈3.4 day, ≈3.0 day, ≈2.8 day, ≈2.4 day, ≈2.2 day, ≈2.0 day, ≈1.9 day, ≈1.8 day; and ≈1.7 day are close to integral multiples of 1/4, 1/5, 1/6, 1/7, 1/8, 1/9, 1/10, 1/11, 1/12, 1/13, 1/14, 1/15 and 1/16 of one solar rotation period (≈27.0 day), hence these periods could be sub harmonics of fundamental period (≈27 day). If so, then these results lead to infer some sort of continuous simultaneous oscillations of active regions having integral multiple frequencies and varying amplitudes occurring on the solar disc.
27-day variation Sub harmonics Solar wind Solar cycle Wavelet analysis
This is a preview of subscription content, log in to check access.
We gratefully acknowledge the use of solar wind plasma data from the Space Science Data Centre (http://www.omniweb.gsfc.nasa.gov). The wavelet software provided by C. Torrence and G. Compo is acknowledged with thanks.
Bai, T., Sturrock, P.A.: The 154-day and related periodicities as sub-harmonics of a fundamental period. Nature 350, 141 (1991)
Forbush, S.E.: On cosmic ray effects associated with magnetic storms. Terr. Magn. Atmos. Electr. 43, 203 (1938)
Torrence, C., Compo, G.P.: A practical guide to wavelet analysis. Bull. Am. Meteorol. Soc. 79(1), 6 (1998)
Tsichla, M., Gerontidou, M., Mavromichalaki, H.: Spectral analysis of solar and geomagnetic parameters in relation to cosmic-ray intensity for the time period 1965–2018. Sol. Phys. 294(15), 1–18 (2019)