Solar wind plasma variations with interplanetary magnetic field during solar cycles 22–24

In this paper, we have studied the relationship between the monthly variations of solar wind plasma velocity, interplanetary magnetic field (IMF) and geomagnetic activity index (Ap) during solar cycles 22–24 (1986–2020). The modulation parameter (ζ =\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ = $$\end{document}V * B) is proportional to the product of solar wind plasma velocity, V and strength of the interplanetary magnetic field, B. We have investigated the periodicities and their evolution during solar cycles 22–24 using Fast Fourier Transform (FFT), RobPer periodogram and Continuous Wavelet Transformation methods. The significant periods present in the modulation parameter include the Rieger type, semi-annual period, annual period and quasi-biennial period (mid-term). In this study, we have found that the rotation rate at the base of the convection zone is ~1.30 years. Quasi-biennial oscillations (QBOs) of solar wind plasma velocity, IMF, modulation parameters and Ap have been compared. The modulation parameter appears to be a better representative of the geomagnetic changes than the other two.