科学衛星EXOS-D(あけぼの)で観測された地球磁気圏内電磁流体波

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A large magnetic storm occurred on October 20 and 21,1989. During a magetically disturbed conditions of the storm, ultra-low frequency hydromagnetic waves (ULF waves) were observed by the EXOS-D (Akebono) satellite near the plasmapause at L=3,and at 10 MLT in the dayside magnetosphere. Continuous oscillations of ULF waves with a frequency of 0.02 Hz and 0.01 Hz were observed on October 20 and 21 respectively, during a large negative excursion of the H component magnetic field on the ground. These waves have provided a unique opportunity for studying the oscillation characteristics of ULF waves in the magnetosphere. The oscillation characteristics have been examined on the basis of observed magnetic field data, combined with the simultaneously obtained data from both the electric field and the electron plasma. In these events, the waves were revealed to be elliptically polarized with a counter-clock wise rotation in the plane perpendicular to the main magnetic field with the Poynting flux flowing along the main magnetic field. These characteristics indicate that these waves are pure transverse waves. A 90° phase lag of the E_x component of the electric field with respect to the B_y component of the magnetic field was clearly recognizable for the oscillations observed on October 21. This suggests a standing oscillation of magnetic field line. As for the observed frequency, lower frequency oscillations for the wave of October 21 can be explained by assuming that the ambient plasma contains more heavy ions such as He^+ and O^+, than that of the wave event of October 20,which oscillated with rather a higher frequency.
東海大学の論文

科学衛星EXOS-D(あけぼの)で観測された地球磁気圏内電磁流体波

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