The simplest model for an this is the Chapman profiel , which is used in all models as a basis for the F-region layer. A description of profile parameters on a global scale. From measurements taken at single geographic locations around the globe, the mean diurnal variations of certain ionospheric parameters are calculated. These variations are then described by means of a limited fourier series. Legendre polynomials are then used to interpolate between these series on a gloabl scale.
Information is avalable on the following numerical models.
TEC , the T otal E lectron C ontent model.