Empirical modeling of global ionospheric foF2 response to geomagnetic activity

Abstract

The authors expand the previously developed midlatitude model, providing the relative deviation of foF2 from its monthly median value as a function of local time and Kp, to the global scale. To achieve this, 55 ionosonde stations, having at least 11 years of continuous data, have been selected, and the model was applied to the data from each station separately. Data from each station were grouped into 12‐month bins, every bin containing all the available hourly data within the respective month of the year. The model considers the distribution of the relative deviation along the local time at any fixed moment as composed of a diurnal and a semidiurnal waves, 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 to the data in each bin. Their distribution along the geomagnetic latitude is obtained in three longitude sectors: North America‐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.