Response of the Equatorial Ionosphere to Disturbances in April 2022

The joint use of the total electron content TEC and ionosonde data allows solving a number of problems from testing ionospheric models to environmental forecasts, but equatorial regions are worst provided with both ionosondes and GPS receivers, so for these regions the use of global models is of particular importance. For TEC, these are global GIM maps, for foF2 - models such as IRI and IRI-Plas that allow determining TEC as well. This paper uses GIM JPL maps and IZMIRAN data for 9 equatorial stations Ascension Is, Belem, Cocos, Guam, Darwin, Fortaleza, Jicamarca, Niue, Sao Luis. The aim of this work was to assess the interchangeability of TEC and foF2 parameters in determining the state of the ionosphere and to compare the model and experimental values of these parameters including during four disturbances in April 2022. The correlation coefficients
$\rho$
between TEC and foF2 exceed 0.9, except three stations with
$0.7 < \rho < 0.8$
associated with large scatter of foF2 data. This indicates the interchangeability of the two parameters. The TEC comparison statistics includes a mean error MAE of 14.3 TECU for the IRI model and 9 TECU for the IRI-Plas model, with RMSE values of 17.2 TECU and 11.7 TECU, corresponding to NRMSE values of 42.8 % and 29.6 %. For foF2, the mean MAE error was 1.33 MHz for the IRI and IRI-Plas models and 0.96 MHz for the IRI-Plas model adapted to the observational TEC values. The RMSE values for these three options were 1.63 MHz, 1.65 MHz, and 1.12 MHz, corresponding to NRMSE values of 17.7 %, 18 %, and 12.3 %. The main conclusion is that the use of the global GIM maps and the adapted IRI-Plas model is an acceptable option for determining the ionospheric parameters in equatorial regions not only in quiet conditions, but also in periods of disturbances.