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首页> 外文期刊>Journal of geophysical research >Multispacecraft observations of fundamental poloidal waves without ground magnetic signatures
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Multispacecraft observations of fundamental poloidal waves without ground magnetic signatures

机译：Multispacecraft observations of fundamental poloidal waves without ground magnetic signatures

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摘要

Poloidal standing Alfven waves observed by spacecraft usually have a second harmonic standing wave structure. On very rare occasions, fundamental poloidal waves have been observed in association with giant pulsations observed on the ground. In this paper, we report multisatellite observations of fundamental poloidal waves that did not produce any clearly associated magnetic pulsations on the ground. The waves were observed on 10 November 2008, at similar to 1830 Universal Time (UT) at THEMIS-A and THEMIS-D and at similar to 2010 UT at THEMIS-E as these spacecraft passed L similar to 11 and magnetic local time (MLT) similar to 0900. The GOES-11 geostationary satellite (L similar to 7) also observed poloidal waves at similar to 1730 UT when it was at similar to 0900 MLT. The poloidal waves at THEMIS were characterized by narrow-band oscillations (frequency similar to 4 mHz) of the ion bulk velocity and magnetic field in the radial direction. We identify the waves at THEMIS to be the fundamental mode on the basis of the wave properties observed slightly south of the magnetic equator: large velocity amplitude, small magnetic field amplitude, and similar to 90 degrees phase delay of the magnetic field relative to the velocity. The azimuthal wave number is found to be similar to 70 (if we assume westward propagation) or similar to 200 (if we assume eastward propagation) from the phase delay between THEMIS-A and THEMIS-D. This wave number explains why there were no corresponding magnetic field oscillations on the ground. These observations imply that only a subset of fundamental poloidal waves excited in the magnetosphere is observed on the ground as giant pulsations.

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