Fine-scale morphology and spectral characteristics of active aurora

Sammanfattning: Ground-based and in-situ observations of the aurora demonstrate an extreme richness in fine structure, with spatial scales down to tens of metres and time variations occurring on a fraction of a second. To further our understanding of the aurora, it is esssential to understand the mechanisms responsible for the small-scale structuring, since this is an intrinsic property of the auroral plasma. Still many questions about dynamics and structuring of aurora on small scales remain unanswered. In this thesis the low-light optical instrument ASK (Auroral Structure and Kinetics) is used to image small-scale structures in the aurora at very high spatial and temporal resolution. ASK is a multi-spectral instrument, imaging the aurora in three selected emission lines simultaneously. This provides information on the energy of the precipitating electrons. The SIF (Spectrographic Imaging Facility) instrument has been used in conjunction with ASK, to give a more complete picture of the spectral characteristics of the aurora, and to determine the contamination of the emission lines by other emissions. Data from ASK and SIF is used to study the relation between the morphology and dynamics of small-scale structures in the aurora and the energy of the precipitating electrons. By comparing electron density profiles provided by EISCAT (European Incoherent SCATter) measurements with modeling results, information on characteristic energy and energy flux of the precipitating electrons can be obtained. One of the ASK channels is imaging a metastable O+ emission, which has a lifetime of 5 s. By tracing the afterglow in this channel optically a direct measure of the E × B drift and thus of the local ionospheric electric fields is provided.