Observed Wave Amplitudes Research Articles

Ogo 5 observations of Pc 5 waves: Ground-magnetosphere correlations

Twenty-two months of Ogo 5 flux gate magnetometer data in the years 1968--1969 have been scanned for the occurrence of Pc 5 waves. Such waves were observed on 18 orbits inside the magnetosphere in the region of L=6--13 and at a magnetic latitude of 10degree to approx.30degree. Close correlations between magnetospheric waves and Pe 5 pulsations on the ground were found on 13 orbits. The 15 orbits on which waves were observed in the morning sector of the magnetosphere were between 0300 and 1100 LT. Most Pe5 waves in the morning were left-hand elliptically polarized with respect to the ambient field. The major axis of the polarization ellipse was directed nearly perpendicular to the ambient field and close to the azimuthal direction. The examination of ground Pe 5 pulsations at a conjugate pair of stations. Great Whale (GWR) and Byrd (BY), indicates that the Pe 5 wave, in terms of the simple string analogy of field line resonance, is an odd mode. The radial location, local time of occurrence, and polarization of the waves observed in the magnetosphere are in agreement with expectations based on ground observations. The fact that the waves were observed well inside the magnetosphere suggests thatmore » if the waves are generated by the Kelvin-Helmholtz instability at the magnetopause, then field time resonances must play a role in establishing the observed wave amplitudes. (AIP)« less

Hydromagnetic waves excited during an ssc

The effects of hydromagnetic perturbations that were excited by an ssc were seen at L=8.2, −12° geomagnetic latitude, 0610 geomagnetic local time in Explorer 12 energetic particle and magnetic field data, and on ground magnetograms. The entire day side magnetosphere was compressed by 2–3 RE in 2–3 min. This compression and the accompanying increase in magnetopause currents produced a 25-γ enhancement of the magnetic field at the satellite and a worldwide 45-γ enhancement at the ground. Energetic electron fluxes rose sharply at the satellite, indicating that particles moved earthward and were accelerated as the magnetic field was compressed. An additional 15-γ 2-min enhancement of the magnetic field was seen at the satellite. This pulse did not significantly enhance energetic electron fluxes and did not produce worldwide ground effects, though associated perturbations are present in some ground records. The pulse appears to represent a localized compressional magnetoacoustic wave that was excited by the rapid magnetopause motion. Finally, a damped toroidal oscillation with an initial amplitude of 26 γ, a period of 250 s, and an exponential damping time of 400 s was seen at the satellite. This oscillation could not be seen at any available ground station, the indication being that it was confined in latitude or longitude. The damping could be produced either by the coupling of energy between wave modes or by finite ionospheric conductivity. The wave period agrees with predictions if the density of plasma on the field line varies with radial distance as r−6, with ρ=4 to 12 ions/cm³ at the equator. An initial energy input of 4 × 1020 dL to 2 × 1021 dL ergs can produce the observed wave amplitude, if plasma at all longitudes between the L and the L + dL shells is involved in the oscillation.