Simultaneous observation of Pc 3–4 pulsations in the solar wind and in the Earth's magnetosphere

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Abstract
The equatorially orbiting AMPTE (Active Magnetospheric Particle Tracer Explorers) CCE and IRM satellites have made numerous observations of Pc 3–4 magnetic field pulsations (10‐ to 100‐s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/interplanetary magnetic field (IMF) control of two categories of dayside magnetospheric pulsations: (a) Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. Their periods (including harmonics) appear to be governed by local resonant conditions. Varying levels of broadband compressional wave power are associated with these pulsations, most prominently near local noon, (b) More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. Harmonically structured, azimuthally polarized pulsations also occur in conjunction with these compressional pulsations, but again display frequencies characteristic of local resonant conditions. As in earlier studies there is clear control of the occurrence of pulsations both inside and outside the magnetosphere by the cone angle of the IMF, and harmonic pulsation amplitude increases when the solar wind velocity increases. The observations reported here are consistent with a high‐latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.