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. Key Points: Peak Density Thickness (PDT) formalism that allows the plasma density at the F2 layer profile peak to remain constant with height for tens of kmCombined Incoherent Scatter Radar (ISR) and Digisonde measurements at mid‐latitudeUsing Millstone Hill ISR measurements from 1993 to 2023 to study the ionosphere Peak Plasma Density Thickness (PDT) [ABSTRACT FROM AUTHOR]