Empirical model of O+-H+ transition height based ontopside sounder data Original Research Article

A new model of the O+-H+ transition height (denoted as THM) is developed, based on vertical electron density profiles fromtopside ionosondes. The model provides the transition height as a function of month of the year, local time, geomagnetic latitude, longitude and solar flux F107. To define TH, the O+ scale height is approximated by the lowest gradient in the measured profile and the O+ profile is reconstructed. TH is taken at the height where O+ density becomes half of total electron density. The model data base contains 170,033 TH values, sufficiently sampling all parameterʹs ranges. THM describes the transition height by a multivariable polynomial consisted with Chebishevʹs and trigonometric base functions, which is fitted to the data in the five-dimensional space. The model results are compared with other available models. The comparison shows that THM predictions agree in general with those of the other models, but THM variations along latitude, longitude and local time have larger amplitudes.