Overestimation of the Bottom-Side Ionospheric TEC in the IRI Model Over Low Latitude Regions

Abstract

It is known that the ionospheric Total Electron Content (TEC) variations estimated by the IRI model show large differences from observed values over the low latitudes. While studies on the topside ionospheric contributions to the errors in the modeled TEC by the IRI are under active consideration, there have been no studies on the role of the contribution of the bottom-side ionosphere. As ionosondes provide the true information on the bottom-side TEC, in this work a comparative study has been carried out in discerning the role of various parameters that go into the estimates of bottom-side density profiles and electron content in the IRI model (TECb_iri). The digisonde measurements over a low latitude location, Ahmedabad, India are used to estimate the bottom-side electron content (TECb_digi) during 2015 and 2018. It is found that the TECb_iri is overestimated during day time irrespective of the season and solar activity. The maximum differences in TECb_digi are noted during equinoctial months and high solar activity period. Among the F-layer peak and profile parameters, the model differences in the bottom-side thickness (B0) are found to be consistent with the differences in the TECb_iri. The agreements and discrepancies between TECb_iri and TECb_digi, under the influence of complex electrodynamic processes and solar flux are discussed. This study provides crucial information required to delineate the contributions of different empirical parameters in the IRI to address the discrepancies that exist in the bottom-side ionospheric modeling over low latitudes.