Characterizing plasma peak density thickness in the ionosphere: A single-site multi-instrument study

This paper introduces the Peak Density Thickness (PDT) formalism, a novel approach to representing the F2 layer's vertical electron density profile in the ionosphere. It diverges from the conventional “pointed-peak” model by suggesting a “broad-peak” or “flat-nose” profile where plasma density remains constant within an altitude interval χ. This theory is backed by independent observations, including a comprehensive data set from the Millstone Hill Incoherent Scatter Radar at the MIT Haystack observatory, spanning from 1993 to 2023, which illustrates the presence and diurnal variation of PDT. A single-day intensive cross-verification using Digisonde Portable Sounder DPS4D soundings of the sub-peak ionosphere has shown remarkable agreement in the measurements of the lower boundary of the χ interval and the peak density. This study suggests incorporating the flat-nose section χ into the F-region profile formalism. Such a shift could improve the accuracy of topside specifications derived from ground-based ionosonde measurements, enhancing our understanding of ionospheric plasma dynamics.