High-latitude F2 peak density thickness: a long-term characterization using PFISR measurements

This study examines the Peak Density Thickness (PDT) parameter in Earth’s ionosphere, with a focus on high-latitude regions. PDT characterizes the vertical extent of the ionospheric F2 region and serves as an indicator of how thick the region of maximum electron density is when measurement uncertainty is taken into account. PDT was originally introduced for midlatitude observations at Millstone Hill and later investigated at equatorial latitudes using the Jicamarca Incoherent Scatter Radar (ISR). However, its behavior at high latitudes has remained largely unexplored. To address this gap, we analyzed electron density measurements from the Poker Flat Incoherent Scatter Radar (PFISR) in Alaska spanning the period 2007–2020. Of more than 107,000 available electron density profiles, approximately 66,000 were successfully processed using an automated procedure to estimate PDT, providing a long-term perspective on its variability at high latitudes. To complement the climatological analysis, a two-hour custom ISR experiment was conducted on 28 July 2020, sampling the ionospheric F2 layer during the post-solar noon period. The measured PDT was consistent with previously reported midday values at lower latitudes. In contrast, the long-term PFISR dataset reveals a key high-latitude feature: PDT remains elevated throughout much of the day, unlike midlatitude and equatorial regions where it typically peaks near solar noon. This persistently large PDT at high latitudes is likely influenced by extended solar illumination during summer months and by auroral and geomagnetic processes that can sustain enhanced electron densities even during winter. These results highlight distinct plasma dynamics in the high-latitude ionosphere and underscore the need for continued targeted observations and modeling efforts to accurately represent ionospheric structure in these regions.