Middle and low latitude effects of auroral disturbances from incoherent-scatter

Abstract

This paper presents a review of the main phenomena observed by incoherent-scatter observatories, and related to auroral disturbances, or more generally to magnetic substorms. These phenomena fall in two categories that can be defined as follows. The first one is constituted by direct effects of perturbations in the magnetosphere projected downwards in the ionosphere along magnetic field lines. The equatorward displacement of the midlatitude trough associated with the erosion of the plasmasphere occurring during substorms, falls in this category. Likewise strong disturbances in electric field observed at midlatitude during magnetically disturbed periods are certainly the manifestation of the electric field system which is established in the magnetosphere during substorms, in association with the three-dimensional current system flowing in the L = 6 magnetic shell (this current system involves the asymmetric ring current, the auroral electrojet, and parallel currents along L = 6 magnetic lines). At low latitude, this electric field system is possibly responsible for perturbations of the equatorial electrojet observed during magnetically disturbed periods. The second category consists in perturbations of the neutral atmosphere at low and midlatitude, due to direct energy input into the auroral neutral atmosphere. Two types of perturbations can be distinguished in this category: ‘The short time perturbations’ which are the manifestation of large-scale gravity waves traveling equatorwards. Their dissipation in the upper thermosphere contributes certainly to the thermospheric heating observed during magnetically disturbed periods. ‘The long time perturbations’ consist of a modification of the general circulation with possibly important consequences on the composition, dynamo electric field, etc. After a general look at the contribution of the incoherent-scatter equipments in the investigation of the above phenomena, we propose that special efforts are to be done in the future for setting up coordinated experiments, triggered on alert, for observing ionospheric effects of magnetic storms.