Model of the Equatorial Anomaly in foF 2 Based on Interkosmos-19 Data for High Solar Activity

An empirical model of the equatorial anomaly in the critical frequency foF 2 of the ionospheric F 2 layer is constructed. The model is based on Interkosmos-19 satellite data obtained in 1979–1981 for quiet conditions under high solar activity. The model reproduces the latitudinal, longitudinal, diurnal, and seasonal foF 2 variations within ±70° of magnetic inclination. The equatorial anomaly predicted by the model for any season begins to develop from ~08 LT. The anomaly is clearly expressed until 02 LT and completely disappears at 04–06 LT. The foF 2 distribution in the region of equatorial anomaly has been studied in detail for different seasons and local time hours and was corrected against Interkosmos-19 data earlier; therefore, the model more adequately reproduces the longitudinal variations in foF 2 than the IRI model, especially at the equator and over oceans. As a result, the model also more accurately reproduces the latitudinal foF 2 variations; specifically, the structure of the Weddell Sea anomaly, than the IRI model. The discrepancies between the new model and IRI-2016 for any season peak in the Pacific longitudinal sector, which contains few ground-based stations. The discrepancies are large at midnight (the decay of the equatorial anomaly according to the IRI model begins earlier than it starts according to satellite data) and in the morning at 06 LT (according to IRI, the foF 2 begins to increase much earlier than the sunrise time). The new model is presented in the form of a program on the site of IZMIRAN: https://www.izmiran.ru/ionosphere/eia/ . The program makes it possible to calculate the foF 2 values at each point; the longitudinal, latitudinal, diurnal, and seasonal variations in foF 2; and the foF 2 distribution for fixed LT and UT times.