The ARCAD-3 project and the theory of auroral structures

Abstract

Some results of the Soviet–French ARCAD-3 project (AUREOL-3 satellite) are reviewed and discussed. The system of magnetohydrodynamic equations (up to the second moments, neglecting the others), with a rigorous account of all drifts and currents or trapping, in a curved and convergent field tube is derived for a particle population with a bi-Maxwellian particle distribution and with [Formula: see text]. Its first four integrals are derived for a particular case, when spatial variations of the electric field are much more rapid than those of any other macroscopic parameters or their products. This is a realistic condition for an extended stable double layer in an inverted V structure. A specific feature of these integrals is that the polarization-drift effects inherently affect the field-aligned current (FAC) density carried by a particular population if both field-aligned and perpendicular gradients of the electric field are sufficiently high. This is important for double layers extended along the magnetic field in narrow, oblique inverted V's. A three-dimensional geometry of the plasma-sheet pressure gradients [Formula: see text], [Formula: see text] the FAC's, and the polarization and ionospheric closure currents [Formula: see text], and [Formula: see text] is suggested, which is supposed to lead to the formation of a narrow arc at a side of an inverted-V event. Sample calculation results for a two-dimensional geometry in limited areas of the meridional plane with simplest boundary conditions are shown for illustration.