Consequences of a resistive instability operating in the upper auroral ionosphere

Current models for the origin of discrete auroral phenomena cannot explain extremely thin held aligned layers of auroral luminosity caused by low energy electrons. These very small-scale amoral forms occur both embedded in broader auroral displays and isolated as faint auroral rays. We suggest that a resistive instability operating in and above the topside ionosphere may be a promising candidate for an ionospheric cause of very small-scale auroral phenomena. We investigate this instability process by means I of numerical simulations carried out by a 3D plasma-neutral gas fluid code. Our numerical results show remarkable correspondence to a number of often observed characteristic features of the lower auroral acceleration region (e.g. field-aligned plasma flows, density cavitons, plasma heating) as observed by Freja, EISCAT and rocket missions. (C) 1997 Elsevier Science Ltd.