Phase coherence analysis of a field line resonance and solar wind oscillation

Abstract

Discrete field line resonances (FLRs) are a common occurrence in the magnetosphere. However, the source of the stable, discrete FLR frequencies is still an unresolved problem. Recent work has proposed that discrete, continuous oscillations in the solar wind directly drive magnetospheric FLRs. However, these studies have only concentrated on common frequency and amplitude comparisons. This paper presents a new technique which utilizes either Fast Fourier Transform or wavelet cross-phase measurements to demonstrate a high degree of phase coherence between a 1.7 mHz FLR observed with the SuperDARN Kodiak 'radar and ACE SWE oscillations in solar wind plasma density. A statistical analysis which simulates the solar wind as red noise indicates with 99% confidence that the FLR oscillation is the same as the solar wind plasma density variation. Copyright 2008 by the American Geophysical Union.