Hydromagnetic propagation of sudden commencements of magnetic storms

The curve for the hydromagnetic wave velocity function of altitude, shown in Figure 1, was computed from preliminary ion density calculations of F. S. Johnson [1959] and the observations of C. Y. Johnson and others [1958]. This curve replaces the one previously reported [Dessler, 1958]. Table 1 gives the ion number density, the average ionic molecular weight, and the velocity of hydromagnetic waves as functions of altitude in the equatorial plane. It is likely that the ion density figures used in computing the hydromagnetic wave velocity above 2000 km will be modified (W. B. Hanson and F. S. Johnson, private communication).