The frequency spectrum of Pc 3 and Pc 4 micropulsations observed at Colombo, A station near the geomagnetic equator

Abstract

The analysis of micropulsations in the Pc 3, 4 band at Colombo, an equatorial station, during April 19 and May 24, 1964, indicate: (1) The dominant periods of the Pc 3 and 4 activity are 38±5 and 60±5 sec. (2) The 60-sec peak is highly stable and occurs both in day and night signals. It is also composed of large amplitude signals. (3) The 38-sec peak is constituted from smaller amplitude signals and is enhanced during local daytime and particularly under magnetically disturbed conditions. (4) Midnight pulsations form a broad spectrum with no sharp peaks but a broad peak at 55±10 sec. These pulsations consist mainly of damped oscillations of the Pi 2 type. The observed frequencies are compared with frequencies predicted by several resonance theories.