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Cahill et al. 1984
Cahill, L.J., Sugiura, M., Lin, N.G., Arnoldy, R.L., Shawhan, S.D., Engebretson, M.J. and Ledley, B.G. (1984). Observation of an oscillating magnetic field shell at three locations. Journal of Geophysical Research 89: doi: 10.1029/JA089iA05p02735. issn: 0148-0227.

On July 14, 1982, 1830--1930 UT, a complex magnetic pulsation event was observed near the magnetic shell L~4.5 in the local afternoon. A large magnetic storm was in progress and had proceeded to the early recovery phase. The event began, at 1832 UT, with a sudden decrease in ‖B‖ and a brief, 120-s compressional pulsation. A transverse pulsation then developed with period near 180-s and amplitude about 5 nT. Near 1850 UT this pulsation decreased abruptly and was replaced by a 44-s transverse pulsation. By 1858 UT the 44-s pulsation was fading and a 240-s azimuthal pulsation developed rapidly. It slowly decreased in amplitude after 1910 UT and was gone by 1930 UT. The event was observed at the DE-1 satellite near the equator in both electric and magnetic field components and at the ground magnetic observatories Siple. Antarctica, and Roberval, Quebec, 15 to 30 west of DE-1 and at opposite ends of an L=4.2 field line. The 180-s and 240-s pulsations were fundamental, toroidal, resonant oscillations of a magnetic field shell. Since the first 180-s pulsation started and stopped simultaneously at all three locations and the corresponding magnetic pulsations remained in phase at all three locations, this is interpreted to be a large-scale toroidal oscillation of one resonant field shell. In the 240-s pulsation, DE-1 was on one resonant shell and the ground stations, oscillating at 220 a period, were on another lower L value shell. The 44 a pulsation, also transverse at DE-1, was weaker on the ground and poorly correlated with the DE-1 measurements, suggesting that it was more localized in azimuth.

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Journal of Geophysical Research
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