Investigating different vTEC calibration methods for data assimilation in ionospheric empirical models

Abstract

A new data assimilation procedure in the International Reference Ionosphere UPdate (IRI UP) method has been recently implemented. This new procedure relies on the assimilation of vertical total electron content (vTEC) values from a Global Navigational Satellite Systems ground-based receivers network, calibrated through the Seemala’s method (IRI UP Seemala), to obtain an updated description of F2-peak ionospheric characteristics over the South-African region. The main purpose of this paper is to investigate how the use of different vTEC calibration methods affects the IRI UP method. In this work, the IRI UP method is applied on periods already analysed in the past (several quiet and disturbed periods in 2017 and 2018), but assimilating vTEC values calibrated through the Ciraolo’s method (IRI UP Ciraolo). In this way, it is possible to make a homogeneous and fair comparison between results obtained with the two different calibration methods. Overall, it emerges that IRI UP Ciraolo models foF2 with a precision that is always greater than the IRI UP Seemala’s one, mainly at nighttime and solar terminator hours, for both quiet and disturbed periods; while slight improvements are achieved during daytime hours. Their accuracy is instead quite similar. Anyhow, the IRI foF2 modeling over the South-African region is significantly improved by both procedures, thus providing a valuable tool to improve IRI model performances.