Quoted from: https://ccmc.gsfc.nasa.gov/modelweb/ionos/ni-intercosmos.html
Parameter: Electron temperature at 550 km, 900 km, 1500 km, and 2500 km
Brief Description:
This data set includes several global empirical models of the ionospheric electron temperature based on measurements by the radiofrequency probe and retarding potential analyzer on board the Intercosmos 19, 24, and 25 satellites representing mostly high solar activity conditions. Two models are provided one for equinox and one for solstice conditions. A spherical harmonics representation (up to 8th order) is used in terms of invdip and Magnetic Local Time (MLT). The invdip latitudinal coordinate combines the advandages of the dip latitude at low latitudes with those of the invariant latitude at high latitudes. These models are used in the International Reference Ionosphere.
Availability: Included in the International Reference Ionosphere.
References:
V. Truhlik, L. Triskova, J. Smilauer, and V. Afonin, Global empirical model of electron temperature in the outer ionosphere for period of high solar activity based on data of three Intercosmos satellites, Adv. Space Res. 25, #1, 163-169, 2000.
V. Truhlik, L. Triskova, and J. Smilauer, Imporved electron temperature model and comparison with satellite data, Adv. Space Res. 27, #1, 101-109, 2001.