Characteristics of energy transfer of Pi 2 magnetic pulsations: Latitudinal dependence

To investigate the generation and propagation mechanisms of Pi 2 magnetic pulsations, we have analyzed magnetic field data from the 210° magnetic meridian (MM) stations. We used 50 Pi 2 events that were simultaneously observed at seven stations along the 210° MM during January 1995, and focused our analysis on associated magnetic energy, ((Δ H )²+(Δ D )²)/µ 0 . The times when the amplitude of the magnetic energy attained the maximum ( T max ) were compared among these stations. We found that T max has a latitudinal dependence, especially at higher latitudes, which has not been previously reported. At Kotel'nyy (L=8.50) on the poleward side of the auroral region, T max occurred an average of 21 seconds earlier than T max at Guam (L=1.01), and often as much as one minute earlier. The existence of latitudinal variation has implications for interpretation of issues related to timing of substorm onset; it is necessary to consider the global features of Pi 2 events in the study of auroral and magnetospheric substorms.