Using RISR-N to Resolve Variations in Dayside and Nightside Plasma Density Spatial-Scales

To provide new insights into plasma density scale-sizes in the polar cap, irregularity spectra are developed and tracked relative to magnetic local time (MLT) and solar zenith angle (SZA). A novel Incoherent Scatter Radar (ISR) technique is applied to develop spectra between 20 and 300 km using 2016 to 2018 imaginglp mode data from Resolute Bay ISR-North. This technique leverages: (a) volumetric plasma density measurements from Advanced Modular ISRs, (b) the slow F-region cross-field plasma diffusion at scales greater than 10 km, and (c) that high-latitude geomagnetic field lines are nearly vertical. The results of this work find that the largest spectral features within periodograms that use sunlit or dayside plasma densities are predominately above 100 km, indicating that structures that are above 100 km are more common than structures below 100 km in dayside/sunlit plasma. However, the opposite is true when plasma is in the dark or on the nightside, where the largest spectral features are predominately below 100 km. This contrast between the dayside and nightside is symptomatic of photoionization generating structures larger than 100 km, highlighting the role of photoionization or E-region shorting in removing structures less than 100 km or driving larger scale-structures more strongly, and the role of other mechanisms (such as flows, recombination, precipitation, and instabilities) in generating small-scale structures. This paper will discuss these findings in detail, as well as discuss forthcoming works.