Occurrence frequency of geomagnetic micropulsations,Pc

An analysis of the occurrence frequency of geomagnetic micropulsations Pc has been carried out using data obtained during the IGY from a world-wide network of stations. From the characteristics of the diurnal occurrence frequency and their latitudinal and longitudinal dependence, the following conclusions are drawn: (1) The occurrence frequency of Pc's increases as the auroral zones are approached from lower latitudes. Also the hour of the diurnal maximum occurrence appears earlier at high-latitude stations. (2) The occurrence frequency of Pc's depends not only on local time but also in part on universal time. The universal-time factor affects the modulation of the diurnal occurrence by about 50 per cent. The time of maximum occurrence of PC's is about 21 hours GMT in the northern hemisphere. In the southern hemisphere the universal-time factor has opposite phase to that in the northern hemisphere. When the universal-time factor is a maximum in the northern (or southern) hemisphere, the north (or south) geomagnetic pole is about 16 or 17 hours LMT. The GMT dependence derived in this investigation shows about 7 hours' difference compared with Troitskaya's conclusion, which was based on data from several stations in the USSR. This article contains supplementary material.