Multiple ground‐based and satellite observations of global Pi 2 magnetic pulsations

Abstract

Four Pi 2 magnetic pulsations, observed on the ground at L = 1.2–6.9 in the interval from 2300 UT on May 22 to 0300 UT on May 23, 1985, provide new evidence of a global nature of Pi 2 pulsations in the inner (L ≲ 7) region of the magnetosphere bounded by the plasma sheet during quiet geomagnetic conditions. In the present study, magnetic data have been collected from stations distributed widely both in local time and in latitude, including conjugate stations, and from the AMPTE/CCE spacecraft located in the magnetotail. On the basis of high time resolution magnetic field data, the following characteristics of Pi 2 have been established: horizontal components, H and D, of the Pi 2 oscillate nearly antiphase and in‐phase, respectively, between the high‐ and low‐altitude stations in the midnight southern hemisphere. Both the H and D components of the Pi 2 have nearly in‐phase relationships between the nightside and the dayside stations at low latitude. The Pi 2 amplitude is larger at the high‐latitude station and decreases toward lower latitudes. The dominant periods of the Pi 2 are nearly identical at all stations. Although a direct coincidence between spacecraft‐observed and ground‐based global Pi 2 events does not exist for these events, the Pi 2 events are believed to be a forced field line oscillation of global scale, coupled with the magnetospheric cavity resonance wave in the inner magnetosphere during the substorm expansive phase.