Experimental study of the formation of inverted-V structures and their stratification using AUREOL-3 observations

Abstract

Abstract. Multiple inverted-V structures are commonly observed on the same auroral zone crossing by a lowaltitude orbiting satellite. Such structures appear grouped and apparently result from an ionospheric and/or magnetospheric mechanism of strati®cation. More than two years of AUREOL-3 satellite observations were analyzed to study their properties and their formation in the framework of the ionosphere-magnetosphere coupling model proposed by Tverskoy. This model predicts some natural periodicity in the electrostatic potential pro®le (and subsequently in the ®eld-aligned current pro®les) that could account for oscillations experimentally observed in the auroral zone, such as successive inverted-Vs. Experimental results obtained during quiet or moderately active periods demonstrate that the number of structures observed within a given event is well described by a`scaling' parameter provided by the hot plasma strati®cation theory and expressed in terms of the ®eld-aligned current density, the total width of the current band, the plasma sheet ion temperature, and the heightintegrated Pedersen conductivity of the ionosphere. The latitudinal width, in the order of 100±200 km at ionospheric altitudes, is relatively independent of the current density, and is determined not only by the existence of a potential dierence above the inverted-Vs, but also by basic oscillations of the ionosphere-magnetosphere coupling system predicted by Tverskoy. The large number of cases studied by the AUREOL-3 satellite provides reliable statistical trends which permits the validation of the model and the inference that the multiple structures currently observed can be related directly to oscillations of the magnetospheric potential (or the pressure gradients) on a scale of $1000±2000 km in the near-Earth plasma sheet. These oscillations arise in the Tverskoy model and may naturally result when the initial pressure gradients needed to generate a largescale ®eld-aligned current have a suciently wide equatorial scale, of about 1 R E or more.