Modeling the Lower Part of the Topside Ionospheric Vertical Electron Density Profile Over the European Region by Means of Swarm Satellites Data and IRI UP Method

Abstract

An empirical method to model the lower part of the ionospheric topside region from the F2 layer peak height to about 500–600 km of altitude over the European region is proposed. The method is based on electron density values recorded from December 2013 to June 2016 by Swarm satellites and on foF2 and hmF2 values provided by IRI UP (International Reference Ionosphere UPdate), which is a method developed to update the IRI model relying on the assimilation of foF2 and M(3000)F2 data routinely recorded by a network of European ionosonde stations. Topside effective scale heights are calculated by fitting some definite analytical functions (α‐Chapman, β‐Chapman, Epstein, and exponential) through the values recorded by Swarm and the ones output by IRI UP, with the assumption that the effective scale height is constant in the altitude range considered. Calculated effective scale heights are then modeled as a function of foF2 and hmF2, in order to be operationally applicable to both ionosonde measurements and ionospheric models, like IRI. The method produces two‐dimensional grids of the median effective scale height binned as a function of foF2 and hmF2, for each of the considered topside profiles. A statistical comparison with Constellation Observing System for Meteorology, Ionosphere, and Climate/FORMOsa SATellite‐3 collected Radio Occultation profiles is carried out to assess the validity of the proposed method and to investigate which of the considered topside profiles is the best one. The α‐Chapman topside function displays the best performance compared to the others and also when compared to the NeQuick topside option of IRI.

The ESA Swarm mission to help ionospheric modeling: a new NeQuick topside formulation for mid-latitude regions

“…Indeed, the effective scale height is an empirical parameter calculated by fitting measured electron density values with analytical functions, in order to obtain the most reliable representation of the topside vertical electron density distribution. Over the years, different techniques have been employed by many authors to model the effective scale height 5 .…”

On the Analytical Description of the Topside Ionosphere by NeQuick: Modeling the Scale Height Through COSMIC/FORMOSAT-3 Selected Data

“…Obviously, (16) confirms that N e goes to zero at infinity but, more importantly, N e decays like an exponential, representing a radial diffusive equilibrium for a single ion species [31]…”

“…The most established ionospheric models, the International Reference Ionosphere (IRI) model [11] and the NeQuick model [12] are not always able to properly represent the real features of the topside ionosphere [13]- [15]; therefore, further studies aimed at improving their topside representation are needed [16]. A part of the debate includes the choice of the mathematical function to use for the topside electron density vertical representation, the most popular being the Chapman [17] or Epstein [18], [19] families of functions [3], [20]- [22].…”

On the link between the topside ionospheric effective scale height and the plasma ambipolar diffusion, theory and preliminary results

“…These vertical scale heights gained the adjective “effective” because they are effective in reproducing the topside electron density profile only when applied to the analytical function used to derive them from either measured topside profiles or measured electron density values at low Earth orbit (LEO) satellite altitude. Different functions were applied by several authors, the most popular being exponential, Chapman, and Epstein families of functions 12 , 20 – 24 . The first studies were based on constant H values, but the growing bulk of topside measurements suggested the need to allow for an increasing trend of H with altitude 13 , 14 , 25 – 27 .…”