Low latitude model of Te at 600 km based on Hinotori satellite data

A new model of electron temperature (Te) variations in the low latitude ionosphere (600 km) has been developed by using Te measurements onboard Hinotori satellite (February 1981-June 1982). The model is based on spline-approximation of the measured Te in 5-dimensional space comprised of solar activity (F10.7), month of the year, local time, geographic longitude and geomagnetic latitude. Each axis is divided into subintervals delimited by a number of nodes. To find Te at a point of interest, spline interpolation from the nearest nodes to the point of interest is used. During the lifetime of Hinotori mission, F10.7 varied between 140 and 230, so the model is constrained to this solar activity range. The geomagnetic latitude range is limited to ±42° due to the low inclination orbit of the satellite. The model error has been evaluated using the whole database, containing 17 months of data (4.2 × 10 ⁵ measured values). The standard (mean square root) deviation of the model from the data is found to be around 14%. A detailed comparison between the model and IRI-95 predictions shows a discrepancy of 100-200 K in most cases, although some larger deviations are also found to occur, Contrary to IRI, the present model captures satisfactorily the morning overshoot and the afternoon enhancement of Te.