The relationship between the IMF magnitude and the frequency of Pc 3, 4 pulsations on the ground: Simultaneous events

Several attempts have been made to predict the strength of the interplanetary magnetic field (IMF) from the frequency of Pc 3, 4 pulsations measured on the ground. The predictive capability of the ground pulsations depends on the relationship which exists between their frequency and the IMF magnitude. It has been suggested that the relationship improves considerably when coincident frequencies between two stations are used.In this paper we show the correlation between the IMF magnitude and the frequency of coincident pulsation events in a network of five stations in the IGS magnetometer array. We do find that the frequency-field strength relationship is very good for the coincident events at the stations with large longitudinal separation ( > 3 h). We also confirm that the frequency taken from a network of ground stations is a better predictor of IMF magnitude than that from a single station.