Theory of Sudden Commencements and of the First Phase of a Magnetic Storm

In previous theories concerning auroras and magnetic storms, interplanetary space was assumed to be void. Because of the recent accrual of evidence, which shows that there exists an interplanetary gas with densities of 100 to 1000 particles/cc, theories are proposed for the commencement and for the first phase of a magnetic storm. The only mcdification necessary for correcting a previous theory is that the geomagnetic impulse caused by the induced currents in the stream is propagated, not with the speed of light as was originally supposed, but with a finite speed which in the neighborhood of the earth approximates to the Alfven velocity. The original theories are outlined along with the modifications to the theory of the first phase of a magnetic storm. Consideration is given for the motion of the quasi-shock wave in the neighborhood of the earth caused by the rapid increase of the earth's magnetic field. Illustrations are given from which it is seen that the disturbance is propagated through the interplanetury gas with the local Alfven velocity. The time of propagation of the disturbance through the gas is derived. (B.O.G.)