Temporal variations of short- and mid-term periodicities in solar wind parameters and cosmic ray intensity

Galactic cosmic rays entering the heliosphere are modulated by solar wind plasma and the associated magnetic field. Solar wind parameters (solar wind speed, plasma density and interplanetary magnetic field) and galactic cosmic ray intensity during solar cycle 23 have been analyzed using wavelet analysis. The global wavelet spectrum of these parameters shows the existence of a variety of prominent short- and mid-term periodicities. The well known one-solar rotation (∼27 days) periodicity is observed in all the considered parameters, while few fluctuations less than one-solar rotation (∼9 and ∼14 days) are observed only in solar parameters. Annual, semi-annual and tri-annual variations are found in the interplanetary magnetic field and a periodicity of ∼200 days is observed in plasma speed and density. Few additional mid-term periodicities, ∼99 days and ∼1.7 years in plasma speed, ∼75 days and ∼1.4 years in plasma density are also observed. In cosmic ray data, in addition to one solar rotation (∼27 days) periodicity, we observed ∼66 days, ∼140 days, ∼260 days and ∼1.3 years periodicities. Our results also show that the temporal behaviors of short-term periodicities of these parameters are almost uniform throughout the cycle length while it is quite different in variations as well as in amplitudes for mid-term fluctuations.

► Short and mid-term periodicities in solar wind and cosmic rays studied using wavelet analysis. ► 9 and 14 day periodicities observed in solar wind velocity, density and magnetic field. ► In addition to short-term periodicity (∼27 days), ∼1.3 year periodicity in cosmic ray data observed. ► Short-term periodicities are almost uniform throughout the cycle length.