Abstract:
On February 21, 1994, at 0903 UT a strong interplanetary shock crossed the Geotail spacecraft while it is at (x, y, z)GSE = (-26.9,60.8, -2.3) Re. The shock hasalso been observed or detected its effect by other satellites such as Imp-8, Goes-6, Goes-7 and Lanl successively. This shock resulted in magnetic index Dst dropped down to lower than -100nT and AE shows an explicit increase. At the same time the geomagnetic field fluctuated intensively, the flux increased of various energetic particles at geosynchronous orbit. These means there are notable energy coupling between the solar wind and the magnetosphere. Gonzalez et al. pointed out the IMF Bz component should be lower than -10 nT and its duration longer than 3 hours for a strong magnetic storm, of which, Dst index lower than -100 nT, but the character of the shock studied in this paper is that there have no long duration of IMF southward Bz event but only large amplitude fluctuation northward and southward in the downstream of the shock, furthermore the enhanced value and average value for the - Bz is lower than that for the +Bz. If we think that the energy transfer from the solar wind into the magnetosphere take place only during IMF Bz component is negative, then this means the rate of energy transferred into ring current is far quicker than the dissipation of the ring current. This result shows that the duration time of southward IMF is not the essential condition for energy transfer from solar wind into the magnetosphere, if the southward IMF has large amplitude and short time-duration, but repeated many times there may be accumulated notable energy in the ring current owing to the rate of ring current dissipation is very slow relative to the rate of energy pouring into the ring current. In addition, for above result we have analyzed the power spectrum property of the magnetic field, it is shown that the disturbance magnetic energy enhanced near five times after the disturbance field crosses the bow shock and the magnetopause. Nakada et al. pointed out that disturbance field in magnetosphere which frequency is in some band would destroy the third adiabatic invariant for some particles but maintain the first and second invariants of them, these particles will spread inward and get energy in this process. The spectrum analysis in this paper shows that the Bz component of the disturbance field in magnetosphere is absorbed notably near 1 × 10-4 Hz, we inferred that this low frequency field may be a reason which resulted in the ring current particles (such as oxygen ion, proton and so on) diffused inward and enhanced their energy, this process have been reported by Fu et al. by means of CRRES/MICS in 2001.
