Near-Earth High-Speed and Slow Solar Winds: A Statistical Study on Their Characteristics and Geomagnetic Impacts

Near-Earth solar winds are separated into two groups: slow solar wind (SSW) with plasma speed [V-sw] < 500 km s(-1) and high-speed solar wind (HSW) with V-sw > 700 km s(-1). A comparative study is performed on the plasma and interplanetary magnetic field (IMF) properties of the near-Earth SSW and HSW, using solar wind measurements propagated to Earth's bow shock nose from 1963 through 2022. On average, HSW is characterized by higher alpha-to proton density ratio [N-a/N-p] (67%), ram pressure [P-sw] (95%), proton temperature [T-p] (370%), reconnection electric field [V B-s] (141%), Alfven speed [V-A] (76%), magnetosonic speed [V-ms] (65%), and lower proton density [N-p] (52%) and plasma-beta (54%) than SSW. In V B-s, V = V-sw, B-s is the southward component of IMF. V-A = B-0/root mu(0 rho), V-ms = vV(A)(2) + V-S(2) , where B-0 is the IMF magnitude, mu(0) is the free space permeability, rho is the solar wind mass density, and V-S is the sound speed. beta is defined as the plasma pressure to the magnetic pressure ratio. The geomagnetic activity is found to be enhanced during HSW, as reflected in higher average auroral electrojet index [AE] (213%) and stronger geomagnetic Dst index (367%) compared to those during SSW. The SSW characteristic parameters N-a/N-p, T-p, B-0, V-A, and V-ms exhibit medium to strong correlations (correlation coefficients r = 0.51 to 0.87) with the F-10.7 solar flux, while beta and Mach numbers exhibit strong anti-correlations (r = -0.82 to -0.90) with F-10.7. The associations are weaker or insignificant for HSW.