A Note on the Classification of Geomagnetic Signals Below 30 Cycles Per Second

Simultaneous measurements in the frequency range 0.003 to 30 c.p.s. at a number of widely spaced stations have led to the identification of two general micropulsation classes, impulsive and regular, as well as to an adjacent but independent extremely low frequency (e.l.f.) background. The signal bandwidths and the dependence on geomagnetic latitude and longitude serve to distinguish the classes.