Validation of NeQuick topside ionospheric formulation using selected
COSMIC/FORMOSAT-3 data and possible improvements
Abstract
We examine systematic differences between topside electron density
measurements and different topside model formulations including
ground-based α-Chapman extrapolated topside electron density profiles
from auto scaled ionograms, International Reference Ionosphere Model
(IRI-2016) NeQuick topside estimations and a recently improved NeQuick
(Corrected NeQuick) topside formulation. The selected topside electron
density measurements considered were taken, from radio occultation
electron density profiles on board low Earth orbit (LEO) satellites from
the COSMIC/FORMOSAT-3 mission, in the vicinity of digisonde stations on
a global scale. A subset of these radio occultation profiles, with
matched (within 5%) peak NmF2 and hmF2 characteristics is also
exploited to focus the comparison to a high quality validation dataset.
The comparison shows that α-Chapman and Corrected NeQuick underestimate,
whereas IRI-NeQuick overestimates COSMIC topside electron density
observations. The key parameter g which controls the change of scale
height w.r.t. altitude near the F region peak is optimised to a value of
0.15 (compared to a currently adopted value of 0.125). The Corrected
NeQuick topside formulation using the optimised g value of 0.15
(represented as Newg) outperforms all other topside
formulations.