Abstract
[1] A test particle simulation has been performed in order to reproduce the interaction between protons and time-dependent electromagnetic fluctuations in the magnetotail current sheet. The three-dimensional model takes into account a dawn-dusk electric field component E0y, a magnetic field reversal Bx(z), and a constant component Bn along the z direction. Electromagnetic perturbations are generated by random oscillating “clouds” moving in the (x, y) plane. The simultaneous presence of stochastic time-dependent fluctuations and 3-D large-scale fields gives rise to a rich variety of phenomena that are studied by varying the size and shape of the oscillating clouds. The main findings are as follows: (1) the efficiency of the Fermi-like interaction between test particles and moving clouds is largest close to z = 0, where the large-scale magnetic field is weakest; (2) in times of 1–2 min protons can reach energy values up to 50–70 keV, which is beyond the maximum potential drop due to the presence of E0y; (3) the ion energization grows with the size of the magnetic clouds, while it is slightly influenced by the thickness of the clouds along z, confirming that the main acceleration takes place in the quasi-neutral sheet; and (4) assuming parameters of the model corresponding to those of the Earth's magnetotail, it is found that many observed features, such as the formation of a beam in velocity space and non-Gaussian velocity distributions, can be reproduced.
Published Version
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