Propagation characteristics of ULF waves in the Earth’s magnetosphere as inferred by an analysis of polarization parameters of geomagnetic pulsations at a low latitude station

Abstract

We have conducted an extensive statistical analysis of the polarization characteristics of geomagnetic pulsations (10-100 mHz) recorded at L’Aquila (Italy, L = 1.6) during 15 years (1985-1999). The dependence on frequency, local time, season, solar cycle and interplanetary magnetic field orientation has been investigated. The diurnal pattern of the dominant sense of polarization suggests the presence of two distinct sources of ULF waves, one located 1-2 hours before noon and the other one around midnight. Significant variations of the ellipticity occur at sunrise and sunset with clear seasonal dependence. The results are discussed in terms of combined effects of exogenic wave sources, field line resonant mechanism and ionospheric influence.