Long‐duration Pc5 pulsations observed by geostationary satellites

Abstract

Using magnetic data from GOES 2 and 3 geostationary satellites for the year from June, 1979 to May, 1980, we found five Pc5 events which lasted longer than five hours. All these Pc5 pulsations were compressional oscillations occurring during the daytime in the recovery phase of large magnetic storms. The amplitude of the pulsations observed by GOES 3, which was located near 5°N magnetic latitude, was larger than those observed by GOES 2 near 10°N. The source region for the Pc5 waves seems to be limited in latitude and extended in longitude. The mean wave period was longer in the morning and evening than near noon; moreover the period changed quasi‐periodically with the average period of about one hour. This fact may indicate a Doppler shift in frequency due to the motion of the source or a variation of plasma density at the source.