Statistical Study of Magnetic Impulse Events in Ground-Based Magnetic Records

Single Hall current loops in the ionosphere, produced by short-lived, 'impulsive', charge injections into the E-region, produce unique signatures in the magnetic records at a ground-based site. We have developed a set of computer algorithms, concentrating on the impulsive changes in the vertical magnetic component, to automatically search magnetic records and to select impulsive magnetic events which satisfy predetermined criteria. The results of a statistical study of one year of data from the near-conjugate stations South Pole and Iqaluit show that the number of events is largest for the local time (LT) interval 0800 to 1100; there is a sharp decrease in events at 1100-1200 LT. Relationships of these events to theoretical considerations of magnetopause processes such as solar wind plasma injection and flux transfer events are discussed.