Observations of Polar Cap Patch Substructures by EISCAT Svalbard Radar

Abstract

This thesis discusses substructures within convecting large-scale plasma density enhancements, known as “patches”, in the polar F-region ionosphere. Two days of high resolution EISCAT Svalbard Radar (ESR) data from both antennas have been analyzed; the 42m fixed antenna measures along the magnetic field, providing well defined altitude profiles, and the 32m steerable antenna which was directed towards north, is used to measure velocity. Patches have been identified by using the factor 2 from background increase in F2 region maximum electron density (F2). This has been compared with variations in the total electron content (TEC), which is the integrated electron density from 100 to 800 km. Due to satellite clutter and noise above 600 km, F2 is the preferred parameter for polar cap patch identification by ESR. In preparation for the University of Oslo‟s CubeSTAR space weather satellite to be launched in 2010, the F2 search for patches has been compared with a search for patches measured by ESR at satellite altitudes (between 650 and 750 km). The number of patches at these heights increased considerably from those identified by F2, while the patch density decreased by a factor 5-7 from F2. The increased number of patches at satellite altitudes is possibly related to ion upflow events, which is a characteristic signature of the ionospheric cusp. Patches moving north along the 32m antenna beam had sizes ranging from 70 km to 400 km and velocities from 160 m/s to 1km/s. Within these patches, as well as within the tongue of ionization (TOI), there are significant substructures down to km scale size. The EISCAT patch observations have been compared with 250 MHz scintillation and CUTLASS data, which reveals smaller scale structures within the patches. The scintillation index peaked near the edges of polar cap patches, and did not necessarily give the greatest values where the highest densities were observed.