Pc 1 pulsation sources, •. _ p , __, 2790, 1975. proton energies, J. Atmos. Terr. Phy•s., 41, Fukunishi, H., Occurrence of sweepers in the 293, 1979. evening sector following the onset of magne-Jacobs, J. A., and T. Watanabe, Theoretical notes Fukunishi et al.: Classification of Hydromagnetic Emissions 9039 on whistlers and periodic emissions in the hy-tion region by a statistical analysis of ground dromagnetic regime, Planet. Space Sci., 1__5, 'based observations, Planet. Space Sci., 2__•, 799, 1967. 993, 1975. Kangas, J., T. Pikkarainen, Yu. Golikov, L. Saito, T., Geomagnetic pulsations, Space Sci. Baransky, V. A. Troitskaya, and V. Sterlikova, R. ev.., 10, 319, 1969.

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.

The spectral characteristics of magnetic Pi 2 pulsations are studied in detail using data obtained simultaneously over a wide latitudinal range from the auroral region (L=7.5) through low latitudes (L=1.8). Pi 2 is revealed to be observed almost simultaneously with the onset of a substorm expansion over the wide latitudinal range with the common predominant period. The Pi 2 amplitude shows a primary maximum at the auroral oval and an additional secondary maximum near the plasmapause. The Pi 2 period generally becomes shorter (longer) when the associated auroral breakup starts at lower (higher) latitudes. Pi 2 is also observed simultaneously at a pair of conjugate stations in the auroral region with similar waveforms. These observational results support the torsional oscillation model which suggests that Pi 2 is caused by the hydromagnetic torsional oscillation of the geomagnetic field line anchored on the auroral oval.

167 SSC events have been studied by using the data observed at the multiple satellites at the geosynchronous altitude. The strong local time asym metry of the SSC amplitude which was found by KOKUBUN (J. Geophys. Res., 88, 10025, 1983) has been confirmed. The pronounced local time asymmetry has also been found with the direction of the initial movement of Psc magnetic pulsa tions. Those local time effects are interpreted by the intensification of the mag netopause surface current during an SSC event, and by the distance between the geosynchronous satallite and the surface current. It has also been clarified that the SSC signal propagates with a speed of 400-700 km/s across the field lines in the magnetosphere as suggested by WILKEN et al.

SSC events at the geosynchronous altitude have been studied using the data obtained at the geosynchronous satellite, SMS/GOES, as well as the data obtained on the ground for the period from 1976 to 1980. In the compressional component (parallel to the ambient magnetic field direction), the SSC amplitude is very large in the noonside, while it becomes smaller with increasing distance from the noonside and is very small or none in the midnightside. In the transverse component (east-west direction), the direction of the initial movement of Psc changes drastically across the noon and the midnight. The direction is eastward in the morningside, while it is westward in the eveningside. These observational results will be examined quantitatively in the present study.