Plasma structuring within an expanded polar cap and cusp studied with the SS-520-3 sounding rocket.

Abstract: The SS-520-3 sounding rocket was launched on November 4th, 2021 as part of the Grand Challenge Initiative - Cusp from Ny-Ålesund, Svalbard. The rocket was launched into the cusp ionosphere during the main phase of a geomagnetic storm. In this study we utilize two low energy particle analyzers as well as a multi-needle Langmuir probe and an impedance probe as part of the rocket payload. This study aims to provide an overview of the flight conditions from a range of ground-based instruments and scintillation receivers. We were able to confirm that the rocket entered the cusp through the poleward edge at around of northern geographic latitude. Additionally, the rocket encountered polar cap patches (PCP), as well as a patch within the cusp (CP) and a newly-formed tongue of ionisation (TOI). Analysis of the density variations within different scale sizes show enhancements within meter-size and kilometer-size scales on the edges of PCP, within the CP and TOI. Overall, the enhancements within the variations on all sizes, as well as enhancements of the electron density were significantly higher within the CP and TOI in comparison to the PCP, though all structures were encountered at similar altitudes. The strongest enhancements were found on the poleward edge of the TOI, corresponding to strong fluctuations within the electron density. The TOI also had the largest enhancements within gradients of kilometer-size in comparison to meter-sizes. As the TOI is convecting with respect to the background plasma, the edges are susceptible to instabilities like the Kelvin-Helmholtz instability (KHI) and Gradient-Drift instability (GDI), giving rise to plasma density structures on several scale sizes.