Correlation of solar activity proxy with solar wind dynamic pressure in the last five solar cycles

Solar variability related to the magnetic activity can be quantified using synthetic indices (e.g., sunspots number) or physical ones (e.g., chromospheric proxies). To connect solar surface variability and its features in the near-Earth, we use Ca II K index and solar wind OMNI data in the time interval between 1965 and 2019, which almost entirely covers the last 5 solar cycles. Using long-term averaged data, anti-correlation between Ca II K index and solar wind dynamic pressure at 1 AU has been found during solar cycles 20 and 21, while this relation seems to change over the last 3 solar cycles.