Physics Department, University of QueensLand, Brisbane, U.K.
Abstract:
The very-low-frequency emission known as “chorus” has been studied for four Australian recording stations. The phenomenon exhibits a maximum of occurrence at about geomagnetic latitude 60° and occurs only about one-tenth as frequently at geomagnetic latitude 45°. It was never definitely observed at geomagnetic latitude 35°. Marked diurnal variations are present with morning peaks for all stations and also an evening peak at Adelaide and Hobart. Analysis of the diurnal variations suggests that two different mechanisms are involved. The average strength of chorus increases with increasing value of K-index at lower latitude stations and shows a maximum at moderate values of the index for geomagnetic latitude 61°. This is interpreted as meaning that the region of maximum average-chorus-strength moves towards lower latitudes at times of magnetic disturbance.