Some Characteristics of Large Amplitude Pc5 Pulsations

Abstract

An analysis of the 1967 geomagnetic data from five Canadian observatories reveals that Pc5 pulsations of amplitude ;;.40 nT occur most often within geomagnetic latitudes 65°-74°. The occurrences peak during morning hours in the auroral zone but during later hours of the day at higher latitudes, while a strong midnight occurrence peak is also noted at the auroral zone stations. The occurrences and amplitudes in general are found to be largest near the central line of the auroral zone, while the periods are found to increase with increasing latitudes. Stronger magnetic activity seems to generate a larger number of Pc5 pulsations with large amplitudes. With increasing activity, there seems to take place a continuous decrease in the level at which instability develops. This may be inferred from the Baker Lake data, where the period of pulsations decreases continuously with increasing activity. The results of the present investigation seem to fit a model in which the auroral zone ionosphere acts as an amplifier of the amplitude of hydromagnetic waves which arrive along the lines of force from the magnetopause.