A Digital Method for Computation of Time-varying Power Spectra Applied to Geomagnetic Pi Pulsations

Abstract

A digital method of computing time-varying power spectra involving complex demodulation followed by low pass filtering is described. The method is illustrated by an application to records of geomagnetic Pi pulsations from Macquarie Island. These show a steady decrease in power with increasing frequency in the range O· 1---{)' 5 Hz.