A linear scale height Chapman model supported by GNSS occultation measurements

Abstract

Global Navigation Satellite Systems (GNSS) radio occultations allow the vertical sounding of the Earth's atmosphere, in particular, the ionosphere. The physical observables estimated with this technique permit to test theoretical models of the electron density such as, for example, the Chapman and the Vary‐Chap models. The former is characterized by a constant scale height, whereas the latter considers a more general function of the scale height with respect to height. We propose to investigate the feasibility of the Vary‐Chap model where the scale height varies linearly with respect to height. In order to test this hypothesis, the scale height data provided by radio occultations from a receiver on board a low Earth orbit (LEO) satellite, obtained by iterating with a local Chapman model at every point of the topside F2 layer provided by the GNSS satellite occultation, are fitted to height data by means of a linear least squares fit (LLS). Results, based on FORMOSAT‐3/COSMIC GPS occultation data inverted by means of the Improved Abel transform inversion technique (which takes into account the horizontal electron content gradients) show that the scale height presents a more clear linear trend above the F2 layer peak height, hm, which is in good agreement with the expected linear temperature dependence. Moreover, the parameters of the linear fit obtained during four representative days for all seasons, depend significantly on local time and latitude, strongly suggesting that this approach can significantly contribute to build realistic models of the electron density directly derived from GNSS occultation data.

Coincident Observations by the Kharkiv IS Radar and Ionosonde, DMSP and Arase (ERG) Satellites, and FLIP Model Simulations: Implications for the NRLMSISE‐00 Hydrogen Density, Plasmasphere, and Ionosphere

“…Also, our results are supported by the need in increase of the electron density scale height above F2‐layer peak recently confirmed with direct radio occultation GPS measurements (Hernández‐Pajares et al, ; Olivares‐Pulido et al, ).…”

Electron density extrapolation above F2 peak by the linear Vary‐Chap model supporting new Global Navigation Satellite Systems‐LEO occultation missions

“…These results are well maintained when the maximum available SLTA value, h 2 , is increased: just a slight overall improvement (reduction of relative error of about 2%) is obtained for h 2 =550 km, compared with the EPS‐SG case of h 2 =500 km studied in this work. This last result is compatible with the accurate description given by the Vary‐Chapman model under the assumption of scale height linearly dependent with the altitude at the topside part of the EDP, as detailed in Olivares‐Pulido et al [].…”

Spatial and Temporal Features of the Topside Ionospheric Electron Density by a New Model Based On GPS Radio Occultation Data

“…Some interesting features can be verified in the estimated spatial distributions of H 0 , which were obtained with similar magnitude as in previous works (Liu et al, ; Olivares‐Pulido et al, ) and with similar magnitude of H s derived from the neutral temperature of IRI ( H IRI ). A similar consistency of H 0 and H 1 was obtained, with small differences due to the contribution of ∂ H 0 /∂ h .…”

“…Olivares‐Pulido et al () have found that linear functions can be used to well estimate the variability of the scale height at the topside when adjusted to RO data, finding the Pearson coefficient above 0.98 for more than 72% of the analyzed RO ionospheric profiles. In this regard, the varying scale height is approximated as the following linear equation: where H 0 stands for the scale height referred to the peak height and ∂ H 0 /∂ h to the gradient of H 0 .…”

“…In this regard, the varying scale height is approximated as the following linear equation: where H 0 stands for the scale height referred to the peak height and ∂ H 0 /∂ h to the gradient of H 0 . In Olivares‐Pulido et al (), a two‐step procedure was applied to the determination of H 0 and ∂ H 0 /∂ h . First, z was iteratively obtained based on electron density data, and second, a fitting of the linear function given by equation was carried out.…”