STATISTICAL-SURVEY OF AURORAL LATITUDE PC-5 SPECTRAL AND POLARIZATIONCHARACTERISTICS

Recent magnetometer and HF radar observations have indicated the exist ence of multiple, discrete field line resonances with remarkably stabl e frequencies of 1.3, 1.9, 2.6, and 3.4 mHz, apparently driven by MHD waveguide/cavity modes in the magnetosphere. Given the dynamic nature of the magnetosphere, the apparent stability of these frequencies is d ifficult to understand, and it is therefore important to examine this question on the grounds of a larger database. In this paper we present a statistical survey of the occurrence of Pc 5 field line resonance f requencies based on 1 year of data from several stations of the CANOPU S magnetometer array. Pure state filtering techniques were used to inv estigate various statistical aspects of amoral latitude Pc 5 character istics, with emphasis on the occurrence of preferential, discrete spec tral peaks. A number of case studies exploiting the full spatial exten t of the CANOPUS array were carried out to complement the statistics. Although the results provide further support for the existence of disc rete (spatially monochromatic) field line resonances, we find that the apparently stable frequencies do not seem to be particularly distingu ished from other Pc 5 frequencies, except perhaps the 1.9-mHz peak. Di screte field line resonance characteristics were also observed for oth er sets of frequencies, and we therefore conclude that the apparently stable waveguide/cavity mode frequencies do not necessarily represent a unique set. The implications of these results with respect to variou s possible Pc 5 wave generation mechanisms are discussed.