### Papers from SWICo members

Alessio Pignalberi, Michael Pezzopane, David R. Themens, Haris Haralambous, Bruno Nava, Pierdavide Coïsson

The topside part of the ionosphere extends from the F2-layer peak, corresponding to the ionospheric electron density maximum, to the plasmasphere. Developing a reliable model of the topside ionosphere is one of the most difficult tasks because instruments commonly used to probe the ionosphere, namely ionosondes, are only capable of sounding the region below the F2-layer peak. The topside ionosphere is characterized by a monotonic decrease of the electron density as the ion population smoothly transitions from the heavy O^{+} ions to the lighter H^{+} and He^{+} ions. This behavior is described by means of monotonically decreasing analytical functions dependent on a parameter called topside scale height whose exact description is the most challenging task for the topside ionosphere modeling.

In this paper, the analytical description of the topside ionosphere included in the NeQuick model is deeply analyzed. The NeQuick modeled scale height behavior is first studied at infinity and then for the lowest part of the topside region through an expansion in Taylor series near the F2-layer peak. The significant influence of the NeQuick topside parameters in the modeling of the topside profile is investigated in detail and, in particular, it is shown that for the lowest part of the topside the model assumes a linearly increasing trend of the topside scale height. Afterwards, the NeQuick topside formulation is inverted to derive a fully analytical expression of the topside scale height as a function of the electron density and F2-layer peak parameters. This expression has been applied to a selected and very reliable dataset of COSMIC/FORMOSAT-3 Radio Occultation profiles. The performed statistical analyses strongly support the supposed linear trend of the topside scale height for the lowest part of the topside ionosphere, as embedded in NeQuick; thus, the developed technique might be relevant for Space weather modeling purposes.

**Publication**: A. Pignalberi, M. Pezzopane, D. R. Themens, H. Haralambous, B. Nava and P. Coïsson, “On the Analytical Description of the Topside Ionosphere by NeQuick: Modeling the Scale Height Through COSMIC/FORMOSAT-3 Selected Data,” in *IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing*, vol. 13, pp. 1867-1878, 2020, doi: 10.1109/JSTARS.2020.2986683.

https://ieeexplore.ieee.org/document/9072529