Solar Origins of Short-Term Periodicities in Near-Earth Solar Wind and Interplanetary Magnetic Field

This study investigates the solar origins of short-term periodicities in the near-Earth solar wind and interplanetary magnetic field (IMF) using long-term observations (1995–2024) and Potential Field Source Surface modeling. We establish that the 27-day periodicity in solar wind speed and its harmonics (13.5-day and 9-day) are governed by the combined influence of polar and low-latitude coronal holes. Polar coronal holes serve as the fundamental stabilizers of the global coronal structure, while the rotation of the Sun in the presence of low-latitude coronal holes acts as the primary mechanism generating periodic fluctuations. The absence of low-latitude coronal holes diminishes or erases these periodicities. For IMF components forming the Parker spiral, the periodicity is controlled by the structure of the heliospheric current sheet (HCS). A stable 27-day period emerges under a two-sector IMF configuration (HCS average slope SL>0.4, latitudinal extent beyond ±30°), while a stable four-sector structure (SL>0.6, latitudinal extent beyond ±60°) superimposes a clear 13.5-day periodicity. However, periodicity weakens or disappears when the HCS is flat and equatorial, or when global structural changes and transient disturbances disrupt recurrence patterns. In contrast, BzGSE exhibits weak periodicity due to its transient nature, while BzGSM shows intermittent 27-day periodicity modulated by the Russell-McPherron effect. Consequently, geomagnetic indices (Kp, Dst, AE) display periodic behavior similar to BzGSM, consistent with its crucial role in solar wind-magnetosphere coupling. These results quantitatively link solar surface morphology to heliospheric recurrence, clarifying the conditions under which periodicities emerge or are suppressed throughout the Sun-Earth system.