Polar Cap Patch Observations and Modeling in Realistic Geometries

Patches of high-density plasma (100-1000 km scales) are commonplace in the polar cap F-region ionosphere. For northward IMF conditions they typically separate from the dayside cusp ionosphere and propagate across the polar cap; often destabilizing along the way and producing radio scintillation. While the general theoretical construct for these instabilities is well developed, gaps still exist in the understanding and characterization of ionospheric plasma instabilities across a range of time and length scales. Observational data from sources such as Incoherent Scatter Radars (ISRs) have filled some gaps, within the constraints of their temporal and spatial resolutions. Computer simulations have provided additional detail but are limited by the extent to which their initial conditions accurately portray actual plasma patch conditions at instability onset.

Building upon the efforts of Larmarche et al. (2022), which demonstrated (through use of Resolute Bay ISR (RISR) and radio beacon data) significant VHF scintillation concurrent with the passage of a polar cap plasma patch structure, the present effort seeks additional insights into polar cap patch instability dynamics through the use of computer simulations initiated with corresponding real-world observational data of early-stage instability development. Preliminary work with the GEMINI ionosphere model (https://github.com/gemini3d) along these lines, using RISR derived parameters (electron density and drift velocity) of the patch as the initial conditions of the simulation, indicate Gradient Drift Instability (GDI) dominates the production of scintillation inducing small-scale irregularities. Particular emphasis of this follow-on work is analysis of the mid- to late-stage evolution of the instability, characterization of diffusion and mixing within the patch, and mesoscale redistribution of the plasma components, especially once structures break through the edges of the plasma patch. Finally, analysis is conducted on how the spectra of plasma irregularities evolve over time.