Modeling the storm-time deviations of foF2 on a global scale Original Research Article

An empirical model is developed, describing the distribution of the relative deviation of foF2 from its median (denoted as Φ) on a global scale. At any fixed moment Φ is composed by diurnal and a semidiurnal standing waves around the local time. The standing waves are expressed by five parameters: daily mean (average offset), diurnal and semidiurnal amplitudes and phases. The model expression is scaled by a modified function of Kp, which reflects the delayed reaction of foF2 to Kp changes. The model parameters are determined by fitting the model expression separately to the data from each of the selected 55 ionosonde stations. Their distribution along the geomagnetic latitude is obtained in three longitude sectors: North–South America, Europe–Africa and East Asia–Australia. The seasonal symmetry of model parameters in the Northern and Southern hemispheres, which is found to be acceptable, allows the use of parameter values from both hemispheres in obtaining their latitudinal profiles. In order to produce global distribution of each of the model parameters, the respective latitudinal profiles from the three sectors were averaged and approximated by analytical expressions.