ELECTRON DYNAMICS IN 2-DIMENSIONAL AND ONE-DIMENSIONAL OBLIQUE SUPERCRITICAL COLLISIONLESS MAGNETOSONIC SHOCKS

Two- and one-dimensional fully electromagnetic, bounded, particle (for both electrons and ions) codes are used in order to study electron dynamics in collisionless magnetosonic shocks propagating in supercritical regime and quasi-perpendicular direction (90-degrees > theta0 > 45-degrees); theta0 is the angle between the shock normal and the upstream magnetic field. The purpose of the study consists in comparing electrons behavior in one-dimensional (''pseudo-oblique'') nonresistive shocks and in two-dimensional resistive oblique shocks. Resistive effects related to plasma microinstabilities can be self-consistently included in two-dimensional particle codes in contrast with one-dimensional particle codes. Present two-dimensional results reproduce local electron distribution functions (in particular, downstream ''flat tops'') in a self-consistent way and in good agreement with observational results. On the other hand, one-dimensional results exhibit either local enlarged Maxwellian distributions with a partial tail, or a flat top distribution according to the particle density n. These results emphasize that (1) the differences observed between one- and two-dimensional codes may be explained in terms of a critical particle density n(c) used in the one-dimensional code; (2) the evidence of flat tops in both two- and one-dimensional results (provided that n > n(c)) proves that the macroscopic potential jump at the shock front is mainly responsible for their formation; (3) microscopic effects (herein related to the self-consistent cross-field/field-aligned currents instabilities) may represent a complementary mechanism for filling the flat top distribution; (4) some relaxation of the unstable electron flat top distribution (T parallel-to/T perpendicular-to much-greater-than-to 1) is observed when penetrating further into the downstream region, which means that the main filling mechanisms are localized in the ramp of the shock. Moreover, a detailed study of two-dimensional results shows that both resistive and nonresistive configurations can be easily distinguished for theta0 congruent-to 90-degrees, but not any more for large deviations of theta0 from 90-degrees, for which the self-consistent magnetic field rotates noticeably out of the coplanarity plane at the shock front.