Near-Earth solar wind speed of fast coronal mass ejections

Using solar wind and ground magnetometer data for solar cycles 23–25, extreme-value power-law models are developed that quantify relationships between near-Earth solar wind speed and Sun-to-Earth transit times of interplanetary coronal mass ejections (ICMEs). The models of near-Earth solar wind speed, conditional on ICME transit time, are (a) approximately stable for transit times as short as 15 hr, (b) sublinear, consistent with hydrodynamic drag acting on ICMEs during transit, with linear (ballistic) models not supported by the data, (c) representative of most of the information content of the data, and (d) insensitive to the solar cycle and interplanetary preconditioning. Applying the models to the September 1859 Carrington event (𝑇 =17.6 hours), we estimate an ICME-average speed of 𝑉^𝑎 =102⁢1¹¹⁶⁴₈₉₆ km/s and a 1-hr ICME-maximum speed of 𝑉^𝑚 =157⁢5¹⁷⁹⁵₁₃₈₂ km/s. These estimates indicate that Carrington-class magnetic storms do not require exceptionally extreme solar wind speeds, with values lower than some previous estimates.