Geomagnetic field‐line resonant harmonics measured by the Viking and Ampte/CCE magnetic field experiments

Abstract

We report the first simultaneous observations of multiple harmonic, azimuthally polarized, ULF pulsations at two points along a geomagnetic flux tube in space. In March 1986, the elliptically orbiting equatorial AMPTE/CCE satellite was oriented with the apogee near 0830 hours magnetic local time (MLT), and the orbital plane of the polarorbiting Viking satellite was at 1000 MLT. The satellites were situated within approximately the same flux tube but with an effective separation of approximately 10 Re near L = 8 on the inbound pass of the AMPTE/CCE orbit. Structured harmonic pulsations were observed by the magnetic field experiments on both spacecraft, and they appeared to turn off and on simultaneously at both locations. Both the observations and the relative amplitudes along the magnetic field lines support recent ideas of multiple field‐line resonances of Alfvén waves.