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

Abstract

Near-Earth solar winds are separated into two groups: slow solar wind (SSW) with plasma speed [Vsw] &lt

500 km s−1 and high-speed solar wind (HSW) with Vsw&gt

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 [Na/ Np] (67%), ram pressure [Psw] (95%), proton temperature [Tp] (370%), reconnection electric field [VBs] (141%), Alfvén speed [VA] (76%), magnetosonic speed [Vms] (65%), and lower proton density [Np] (52%) and plasma-β (54%) than SSW. In VBs, V= Vsw, Bs is the southward component of IMF. VA=B0/μ0ρ, Vms=VA2+VS2, where B is the IMF magnitude, μ is the free space permeability, ρ is the solar wind mass density, and VS is the sound speed. β 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 Na/ Np, Tp, B, VA, and Vms exhibit medium to strong correlations (correlation coefficients r= 0.51 to 0.87) with the F10.7 solar flux, while β and Mach numbers exhibit strong anti-correlations (r= − 0.82 to −0.90) with F10.7. The associations are weaker or insignificant for HSW. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.