Periodicity for 50 yr of daily solar wind velocity

Daily mean velocity of solar wind that was surveyed near the Earth's orbit at about 1 au from 1963 November 27 to 2015 November 30 and issued by OMNIWeb is used to look into its periodicity through the Lomb-Scargle periodogram method. As the strongest periodical signal, the solar activity cycle of about 10.4 yr is found in high-velocity wind, but in low-velocity wind, the 9.17-yr cycle appears instead. The rotation cycle of about 27 d and its 1/2 and 1/3 harmonic periods are clearly detected in all-, low-and high-velocity wind, and at their periodograms, several individual periodical peaks appear very close to the peaks of these three periods. The annual period of about 1.07 yr is identified for both all-and low-velocity wind, but not for high-velocity wind after 1994. The 1.68-yr period occurs in all-and high-velocity wind, but does not appear in low-velocity wind. The period of about 2.42 yr appears just in the all-velocity wind after 1994, but its twofold period (about 4.83 yr) appears in both all-and high-velocity wind. The period of about 4.1 yr occurs in all-, low- and high-velocity wind. The possible origin of these periods is discussed.