Fig. 1

Guiding center positions of 1 MeV electrons with pitch angle 90° (top panel) and 10° (bottom panel) in the geomagnetic field. Solid lines and gray circles show magnetic field lines and magnetopause boundary, respectively. Colored solid circles show the trajectories of 32 test electrons which are plotted every 5 s for 30 min. The colors indicate the minimum distance between the electron and the magnetopause boundary