Ion burst event in the earth's dayside magnetosheath

The Medium Energy Particle Analizer instrument on the AMPTE/CCE Spacecraft provided ion angular distributions as rapidly as every 6 sec for H, He, and O at energies of 10 keV to 2 MeV in the dayside magnetosheath whenever the solar wind pressure compressed the magnetopause within 8.75 R(E), the CCE apogee. This paper discusses a burst of energetic particles in the subsolar magnetosheath and its association with rapid changes in the local magnetic field direction in such a way the magnetic field connected the spacecraft to the magnetopause during the enhancement. It is found that magnetosheath angular distributions outside the burst peaked at 90 deg pitch angles, whereas during the burst they exhibited field-aligned streaming either parallel or antiparallel to the magnetic-field combined with a clear earthward gradient. The clear earthward gradients at E not smaller than 10 KeV, the streaming, and the slope change in the burst-time magnetosheath spectrum at about 10 KeV suggest magnetospheric source for the burst-time not smaller than 10 KeV ions and heated solar wind for E less than 10 KeV.