Identifying the plasmapause location from global auroral image data

<p>Identifying the plasmapause location is crucial for forecasting and modelling the radiation belts, as well as larger scale models of the magnetosphere. The ionospheric footpoints of the plasmapause are thought to map to the equatorward edge of the diffuse aurora, with the first direct observation of an undulation of the plasmapause boundary and corresponding auroral features reported by He et al. (2020). Despite the importance of the plasmapause location, we do not have global observations of the plasmapause location.</p><p>We provide a new statistical model of the plasmapause location determined from mapping the equatorward boundary of the observed auroral oval out to the inner magnetosphere. The model uses the equatorward boundary of the auroral oval determined from far-ultraviolet observations from the IMAGE spacecraft from Longden et al. (2010) to provide a statistical estimate of the plasmapause location for different levels of geomagnetic activity. Comparing the results of the statistical plasmapause model to other more direct measurements of the plasmapause shows a good agreement in the nightside local time sectors. </p><p>The results of this analysis show that the equatorward boundary of the auroral oval statistically maps closely to the plasmapause boundary the nightside sectors and provides an alternative use for global auroral image data from the upcoming SMILE mission. </p>

Correspondence between the ULF wave power spatial distribution and auroral oval boundaries

The world-wide spatial distribution of the wave power in the Pc5 band during magnetic storms has been compared with auroral oval boundaries. The poleward and equatorward auroral oval boundaries are estimated using either the British Antarctic Survey database containing IMAGE satellite UV observations of the aurora or the OVATION model based on the DMSP particle data. The “epicenter” of the spectral power of broadband Pc5 fluctuations during the storm growth phase is mapped inside the auroral oval. During the storm recovery phase, the spectral power of narrowband Pc5 waves, both in the dawn and dusk sectors, is mapped inside the auroral oval or around its equatorward boundary. This observational result confirms previously reported effects: the spatial/temporal variations of the Pc5 wave power in the morning/pre-noon sector are closely related to the dynamics of the auroral electrojet and magnetospheric field-aligned currents. At the same time, narrowband Pc5 waves demonstrate typical resonant features in the amplitude-phase latitudinal structure. Thus, the location of the auroral oval or its equatorward boundary is the preferred latitude for magnetospheric field-line Alfven resonator excitation. This effect is not taken into account by modern theories of ULF Pc5 waves, but it could be significant for the development of more adequate models.