Neutral and Ion Dynamics in the Auroral Region

This project proposal concists of 2 subprojects. The aim of subproject A is to understand the physical mechanisms behind naturally enhanced ion acoustic lines (NEIALs) observed with the EISCAT radars, and flickering aurora. Recent advances in optical inst rumentation have revealed that auroral emissions may have spatial structures of the order of 50 meters or less in the direction perpendicular to the magnetic field. Hence, understanding the appearance of the aurora requires knowledge of the origin of such small-scale features and the physical processes taking place within the associated thin sheets or filamentary structures. Precipitation of energetic electrons as well as intense field-aligned currents (which are carried by low-energy electrons) inside th ese structures create conditions favourable for the growth of plasma instabilities. The study of these auroral structures must therefore be related to the study of plasma instabilities. The electron beams and resulting instabilities disturb the local ther modynamic equilibrium. EISCAT observations frequently show greatly enhanced spectra of the scattered signals during such conditions. The purpose of Subproject B is by help of EISCAT/Heating and HAARP to investigate the radio-wave-plasma interaction and determine which instabilities take part in the acceleration and heating of the ionospheric electrons. This is done by observing variations in the enhancements of optical emissions.