Global characteristics of Pc1-2 wave activity and their dependence on geomagnetic activity

We examine Pc1-2 waves (in the frequency range of electromagnetic ion cyclotron (EMIC) waves) excited in the Earth's inner magnetosphere, using 8-Hz magnetic field data obtained with the AMPTE/CCE mission during a ~4.5 yr period of time (DOY 239, 1984 through DOY 009, 1989). The ~4.5 yr time period is much longer than the period examined by Anderson et al. [1992] (~1 yr) and covers a wide range of geomagnetic activity. In this paper, our attention will be focused on the global distributions of the normalized occurrence rate (i.e., occurrence normalized by the total observation times) and its dependence on geomagnetic activity represented by the Dst index. The extended AMPTE/CCE dataset provides statistically significant spatial coverage for both quiet and disturbed geomagnetic conditions. The results indicate higher occurrence rate of Pc1-2 waves in the dayside outer magnetosphere, particularly on the afternoon side, than other magnetospheric regions. Pc1-2 waves in the outer magnetosphere (L > 7) have little dependence on the Dst index, while those observed in the inner magnetosphere (L < 7) were intensified more frequently during storms (Dst ≤ -50 nT) on the dusk side. We will also discuss global distributions of wave properties such as peak power and spectral width, and possible differences in global characteristics between H+ and He+ band waves.