Geomagnetic Disturbance and Velocity of Slow-Drift Solar Radio Bursts

Abstract

A POSSIBLE relation between Type II (slow-drift) bursts of solar radio noise and occurrence of geomagnetic disturbance has been suggested by Maxwell, Thompson and Garmire^1,2 and by Roberts³. Excitation of plasma oscillations by an outward-moving stream of particles that later reaches the Earth provides a model consistent with radio observations and with the known relations between solar flares and geomagnetic disturbance. According to this model, as the particle stream moves outward, radiation is induced at the plasma frequency (or at the critical frequency) at locations in the solar corona of progressively lower density. Thus the observed rate of decrease of frequency can be related to a velocity, if some model of coronal density is assumed⁴. Further, we might expect that particles with high velocity at great heights would be more likely to escape from the solar atmosphere and to cause geomagnetic disturbance than those decelerated to low velocity at large heights. Hartz⁵ has concluded from frequency drifts deduced from observations at single fixed frequencies that such a relation does indeed exist.