UNCLASSIFIED/UNLIMITED UNCLASSIFIED/UNLIMITED Large-Scale Plasma Structure in the Polar and Auroral Ionosphere: Experimental Observations and Modelling

Radiotomography provides observations of ionospheric electron density structure on horizontal scales of tens to hundreds of kilometres. Routine measurements over extended periods of time and geographic areas have the potential for parameterising the structure of the polar and auroral ionosphere. Averaged electron densities characteristic of different ionospheric features, locations, local times, Universal Times, seasons, geomagnetic activity and solar conditions can be compared with ionospheric models and used to test and develop the models. Tomographic images are presented of plasma structures characteristic of the polar and auroral ionosphere. Results from initial comparisons of the measurements with the Sheffield University Coupled Thermosphere-Ionosphere-Plasmasphere (CTIP) model are also discussed. General broad agreement is seen between the model and observations but discrepancies are also evident. The high-latitude ionosphere is a highly structured medium, comprising electron density irregularities over a large range of scale sizes [1]. Of particular relevance to this presentation are enhancements and depletions on horizontal spatial scales of tens to hundreds of kilometres. They include the tongue-of