A Comparison of the Occurrence of Very-Low-Latitude Pi 2 Pulsations with Magnetic-Field and Energetic-Particle Flux Variations (30-300 keV) at Geosynchronous Altitudes

Abstract

The occurrence of Pi 2 pulsations (20-150 s) at very-low-latitude stations is compared with the energetic-particle and magnetic-field variations at geosynchronous orbit during the PROMIS (Polar Region and Outer Magnetosphere International Study) period (March 10-June 16, 1986). Ground magnetometer data from Huancayo, Peru (dip equator, 75°W), and Kuju, Japan (L = 1.2, 135°E), are utilized to monitor the magnetic pulsations, while the particles (electron, 30-300 keV; proton, 145-560 keV) and magnetic fields in space are monitored by geosynchronous satellites S/C1982-019, S/C1984-129, S/C1984-037, GOES-5, and GOES-6. Of 175 Pi 2 events surveyed during the PROMIS period, 110 events are accompanied by electron flux enhancement, and 51 events have a concurrent onset of the field-aligned current (FAC). The FAC events correlated with ground Pi 2 pulsations indicate a local time change in polarities. If currents are assumed to flow along the field lines tailward of the geosynchronous orbit, the polarities are upward in the premidnight sector and downward in the postmidnight sector. We classified Pi 2 events in the nightside sector in several different ways. The results imply that if Pi 2 events in the present study can be assumed to be of substorm origin, then 47% of Pi 2 events occur in regions close to geosynchronous altitude.