Quantifying the azimuthal plasmaspheric density structure and dynamics inferred from IMAGE EUV

[1] The extreme ultraviolet (EUV) imager on the IMAGE satellite provided the first global images of the plasmasphere leading to enhanced understanding of plasmapause structure and dynamics. However, few studies have investigated the structure and dynamics of the inner plasmasphere (regions interior to the plasmapause), which previous in situ observations have shown to often be highly structured. This study is the first to systematically analyze global images of the density structure of the inner plasmasphere by using data from the EUV imager on the IMAGE satellite. We find that the inner plasmasphere exhibits both fine and meso-scale structure characterized by rapid density fluctuations and density enhancements of varying amplitudes (factors of 2–5) and spatial scales (from 10 s of minutes to 6 hours MLT) that occur regularly in the aftermath of geomagnetic storms. The level of variability within the azimuthal structure was found to increase with increasing geomagnetic activity. The observations suggest that some meso-scale azimuthal density structure observed in the inner plasmasphere is from “fossil” plasmapause features entrained inside the expanding and refilling plasmasphere.