A comparison of the different empirical relationships that have been suggested between surface magnetic indices and solar wind velocities

Snyder et al. [1963] have shown that the velocity of the solar wind is correlated with the intensity of surface magnetic disturbances. They presented their data from Mariner 2 as a plot of the daily average velocity of the solar wind against the daily sum of Kp. Maer and Dessler [1964] pointed out that the data as presented by Snyder and co-workers deviated from the straight line least-squares fit for high values of ΣKp. They replotted the data in the form of velocity versus Ap and presented a new straight line least-squares fit.