Analysis of Earth Induction Effects on Ground Based Observations of ULF Pulsations near L=4

Abstract

The use of polarization parameters and amplitudes of spectral components of ULF pulsations observed at the earth's surface as diagnostics of magnetosphere dynamics can often be restricted because of the uncertainties of earth induction effects. The vertical component of the magnetic field, in particular, has been restricted in its use because of its well known sensitivity to the earth's conductive structure. In this paper Parkinson's method and the transfer function method, together with a heuristic approach to induction phenomena, are used to analyze the effects of earth induction on ULF pulsations observed along a latitudinal network of stations near L=4 in the northern hemisphere and in their conjugate region at Siple, Antarctica. Results indicate that earth induction has little effect on the characteristics of pulsations in the Pc3, Pc4 and Pc5 frequency bands at these stations. Preliminary results establish the existence of important temporal variations of the in-phase induction vectors at Girardville and LacRebours and their correlation with external source-field mechanisms.