Harmonically structured ULF pulsations observed by the AMPTE CCE Magnetic Field Experiment

Publisher Website
Google Scholar
Abstract
Spectrograms of ULF waves in the 0 to 80 mHz frequency range have been prepared from magnetic field data obtained by the elliptically orbiting AMPTE/CCE satellite (with an apogee of approximately 8.8 Re. The most prominent feature of these spectrograms (which cover a full 15.6 hour orbit) is the presence of harmonically structured, azimuthally polarized pulsations in the outer magnetosphere during daytime hours. The frequencies of these pulsations decrease with increasing radial distance from the earth, indicating that they represent independent resonances of local magnetic flux tubes. The latitudinal structure of these harmonic pulsations, observed as AMPTE/CCE traveled to ± 16° magnetic latitude, is consistent with accepted field line resonance models. Correlations with IMP 8 satellite data confirm a close connection between appearance of these harmonic pulsations in the dayside magnetosphere and interplanetary magnetic field conditions favorable for the generation of upstream waves. Although we also observe pulsations associated with ring current injections, the monochromatic pulsations predicted by some theoretical models are extremely rare in the dayside AMPTE/CCE data set.