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. 1.0 INTRODUCTION 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-ofionisation drawn antisunward from the dayside ionosphere towards the polar cap, polar cap patches, boundary blobs in the evening auroral region, the main ionisation trough and the polar hole. The associated steep density gradients are of particular concern to the performance of practical navigation and communications radio systems. The basic physical processes responsible for the features are relatively well understood and include photo-production, particle precipitation and plasma transport in the highlatitude convection. However, the relative contributions of these processes at any particular time remain open to debate, and need to be established for full interpretation of the morphology of the electron density distribution at high latitudes. The variability in the occurrence, structure and location of the features means that it is not yet possible to represent them accurately in physical or empirical models. This paper reviews polar and auroral plasma structures observed by radiotomography. Interpretations of the features were supported by measurements made by the international European Incoherent Scatter Pryse, S.E.; Middleton, H.R.; Dewis, K.L.; Wood, A.G.; Whittick, E.L.; Balthazor, R.L. (2006) Large-Scale Plasma Structure in the Polar and Auroral Ionosphere: Experimental Observations and Modelling. In Characterising the Ionosphere (pp. 15-1 – 15-10). Meeting Proceedings RTO-MP-IST-056, Paper 15. Neuilly-sur-Seine, France: RTO. Available from: http://www.rto.nato.int/abstracts.asp. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 01 JUN 2006 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Large-Scale Plasma Structure in the Polar and Auroral Ionosphere: Experimental Observations and Modelling 5a. CONTRACT NUMBER