Equatorial Micropulsations and Ionospheric Disturbance Currents

Abstract

THE early evening maximum of occurrence of regular geomagnetic pulsations, pc, of period 20–30 sec., was first detected on the Earth current recordings obtained at Legon, Ghana, during the International Geophysical Year¹; but more recently, Cardus² has confirmed that the occurrence of evening pc is also a feature of micropulsational activity at other equatorial stations. No satisfactory hypothesis has yet been proposed to explain why this type of geomagnetic activity is a day-time phenomenon at all mid-latitude stations, with a maximum of occurrence and amplitude at approximately mid-day, while, in the region of the magnetic equator, there is an evening maximum of both occurrence and amplitude, with lesser maxima at mid-day and early morning³. Several attempts have, however, been made to relate the occurrence of pc pulsations with ionospheric disturbances, and interesting results have recently been obtained by Campbell and Matsushita⁴, who suggest that the onset of micropulsation storms is associated with an increase in ionospheric disturbance, and by Hope⁵, who puts forward the proposal that the movement pattern of the ionospheric disturbance currents produces maximum geomagnetic activity at different times of the day at high, middle and low latitudes.