Statistical characteristics of the periods of Pi pulsations detected by using an automatic detection method at Memambetsu
This paper reports the statistical characteristics of the period of Pi geomagnetic irregular pulsations detected from the X (north), Y (east), and Z (downward) geomagnetic components of Memambetsu geomagnetic data for 2012 and 2009, which were active and quiet solar years, respectively. The automatic detection method developed in the previous study was used to characterize the onset time, period, and amplitude of the Pi pulsations. These elements of the Pi pulsations were comparable during both 2012 and 2009, regardless of whether they were determined automatically or manually. To facilitate this study, an algorithm was created that chose Pi elements from the three spatial components to create a list that included the onset time of the wave with the maximum amplitude among the X, Y, and Z components. Both the periods and amplitudes of the three components corresponded to individual Pi events. With manual detection we have customarily chosen the period of the wave with the maximum amplitude among the X, Y, and Z components, but with automatic detection we chose the period of the wave based on the correlations with the periods of the three components for 2012 and 2009. The results of the analysis of the 2012 and 2009 data revealed that the differences among the periods of the X, Y, and Z components followed a Gaussian distribution. The periods of the Y and Z components were particularly well correlated with each other. The period of the X component was not significantly correlated with that of either other component. Each of the three components showed magnetic characteristics. The magnetohydrodynamic waves were oriented in different directions relative to the directions of wave propagation and the magnetic field. It might be possible to use the onset times of individual Pi events to determine the start time of each Pi series.