Abstract We study the effect of the solar cycle on various magnetohydrodynamic (MHD) fluctuation modes using the linear mode decomposition technique developed by G. P. Zank et al. We decompose various MHD modes, including propagating modes: Alfvén (forward and backward), fast (forward and backward), and slow (forward and backward) modes, as well as nonpropagating structures: entropy and magnetic island modes, from solar wind intervals during both the minimum and maximum phases of solar cycle 23. We find that the amplitudes of different modes corresponding to fluctuations in density, magnetic field, and velocity vary over the solar cycle, with larger amplitudes observed during the solar maximum compared to the solar minimum. The fluctuating energy of these modes is ∼1.5–4.5 times larger during the solar maximum. The frequency spectrum shows that the entropy mode exhibits the largest fluctuating power among density fluctuations, surpassing the contributions of fast and slow magnetosonic modes during both solar maximum and minimum intervals. For magnetic field fluctuations, the dominant contributors are the magnetic island mode, followed by the Alfvén modes. The Alfvén modes dominate the overall velocity fluctuations. This study provides observational evidence for the influence of the solar cycle on linear MHD modes.
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