Longitudinal phase variations of Pc 4‐5 micropulsations

Abstract

A set of 61 relatively uncontaminated Pc 4‐5 micropulsations from the interval July 1 through October 10, 1974, were examined for longitudinal phase changes. The data were obtained from the east‐west line of magnetometers operated by the University of Alberta over the summer and early fall of 1974. From our analysis a direct correlation between longitudinal phase shift and frequency is found which is of the form m = (1.4 ± 0.4) f + 0.26, where f is the frequency in millihertz and m is the azimuthal wave number derived from the measured phase shift. This relationship indicates a phase velocity which is independent of frequency and whose magnitude is Vϕ ≃ 14 km/s. The sign of the phase shift, and thus the direction of apparent phase velocity, changes abruptly 1–2 hours before local noon. The signals appear to propagate away from this prenoon region toward the terminators; that is, they move westward in the morning hours and eastward during the afternoon hours. Both the magnitude and the sign of this phase velocity are consistent with proposed generation mechanisms which invoke the Kelvin‐Helmholtz instability at the magnetopause boundary.

Statistical analysis of ground based magnetic field measurements with the field line resonance detector

“…These results are in good agreement with previous work presented by e.g. Olson and Rostoker (1978) or Chisham and Orr (1997) among others, who found a very similar distribution of azimuthal wavenumbers of Pc5 events against local time. This dawn-dusk asymmetry is generally attributed to a significant fraction of the FLR events being solar wind driven (e.g.…”

“…With this method it is possible to decompose a wave field of several superposed plane waves without the need of a spatially dense array of stations. Pillai (1989) proved the wave telescope to be a generalized minimum variance technique. Pinçon and Lefeuvre (1991) expanded the method to include multidimensional (vectorial) observables and Motschmann et al (1996) further developed it in order to apply it to multipoint satellite measurements (e.g.…”

A Study of the Association of Pc 3, 4 Micropulsations with Interplanetary Magnetic Field Orientation & Other Solar Wind Parameters.

“…(Southwood, 1974), have been recorded at synchronous orbit (Arthur et al, 1977c;Hughes et al, 1978) and on the ground Lanzerotti et al,, 1972;Olson and Rostoker, 1978); and at both, simultaneously (Arthur and McPherron, 1977a); solar wind velocity has been positively correlated with ground pulsations (Saito, 1964;. It is important to mention that most of the cases analyzed by Lanzerotti et al (1972) gave polarization behavior contrary to that predicted by Southwood (1974), but consistent with .…”

On the coupling of fast and shear Alfvén wave modes by the ionospheric Hall conductance

“…The model assumes an azimuthal dependence of all electric and magnetic fields of the form e imφ where m is the azimuthal wave number (Olson and Rostoker, 1978). All distances are scaled in units of R E (the Earth's radius), θ is the colatitude while θ 0 is the colatitude at the surface of Earth in the northern hemisphere after tracing along the magnetic field from a point (R, θ).…”