Max Planck Institute for Aeronomy, 3411 Katlenburg-Lindau 3, West Germany

High time resolution measurements of energetic particles (E_p > 0.29 MeV, E_e > 0.22 MeV) obtained by the Applied Physics Laboratory, Johns Hopkins University, detector along with magnetic field measurements obtained simultaneously by the Goddard Space Flight Center magnetometer, both aboard the IMP 8 satellite in the distant magnetotail (X_SM » -26, Y_SM » +18, Z_SM » +1.6 R_E) are presented for November 26, 1973, when several of the highest-intensity particle bursts were detected in nearly ~9 years of observations by the IMP and IMP 8 spacecraft. The AE index and magnetograms of auroral stations indicate that this day was moderately disturbed magnetically. The energetic particle bursts were associated with rapid changes in the magnetic field, including both positive and negative excursions in the B_Z component. One of the particle bursts was accompanied by a quasi-periodic north-south fluctuation of the tail magnetic field. The onset of the most intense burst was associated with a rapid change (~28 g in ~4 s) in the B_Z component; during this burst the intensity of ~ 1-MeV protons increased ~20 s later than for ~0.3-MeV protons. The spectral index for protons and electrons varied from ~3 to ~6. The appearance of a particles at > 2.4 MeV and the absence of >2.0-MeV protons suggest the presence of electric fields capable of accelerating particles up to ~ 1 MeV/charge. During the onset of the most intense burst as well as during other times, oppositely directed anisotropies of protons and electrons parallel to the tail field lasting up to ~60 s have been observed, possibly indicating the presence of field-aligned electric fields. Some of the bursts revealed that protons and electrons reached comparable maximum energies of ~1 MeV, but the electron fluxes were mostly smaller by a factor of ~10 to ~100 than the proton fluxes. The intense bursts showed spatially separated beams of protons and electrons exhibiting large tailward anisotropies (~10⁴ : 1 and ~ 10² : 1 front-to-back ratio for protons and electrons, respectively). Other bursts showed both earthward and tailward directed proton anisotropies in association with negative B_Z components. Negative B_Z components were observed to be associated with both closed and open field lines as determined from electron anisotropies. The particle and field observations are discussed in the context of proposed mechanisms for the acceleration of particles during various dynamical magnetospheric processes.

J. Geophys. Res., 86, No. A8, 6727-6738, Aug. 1981