A Study of Magnetic Drift Motion of Particles around the Equatorial Plasmapause by Using the Cluster Observation

On August 7, 2003 the Cluster spacecraft moved through the dayside magnetosphere. The energetic particle spectrometer on board Cluster provided measurements of an extensive range of energy. Besides, satellite measurements of geomagnetic field showed a gradient magnetic field. It is known that an inhomogeneity of the magnetic field leads to a drift of charged particles. In this paper, the drift velocities including gradient drift and curvature drift have been calculated for an energy range from 0.1 to 300 keV via various pitch angles (about 6 to 9 UT). The pitch angles in the magnetic equator via the magnetic mirror location have been calculated near the magnetopause. Besides, the ratio of perpendicular particle energy over total particle energy as a function of equatorial pitch angle has been calculated. The drift velocities depending on the pitch angle for the low energy (0.1 kev) is about 0.01-0.07 km/s and for the higher energies of the particles (300 kev) is about 50-200 km/s between L ≈ 4 to L ≈ 6. The results show that particles with higher energies penetrate the deeper areas of the magnetosphere.