Modeling the plasmasphere to topside ionosphere scale height ratio

A new model of plasmasphere to topside ionosphere scale heights ratio is developed, based on topside electron density (Ne) profiles deduced from the International Satellites for Ionospheric Studies (ISIS)-1 satellite measurements. The model is able to improve operational algorithms for space weather predictions. The topside ionospheric and plasmaspheric scale heights are determined by the lowest and largest gradients of measured profiles, respectively, converted in dh/dlnNe units. The new model depends on four parameters: the month of the year (M), the local time (LT), the geomagnetic latitude (glat), and the ln(O+) density (zO) at the O+-H+ ion transition height. It is designed to replace the old one-dimensional model of the ratio in the TaD (TSM-assisted Digisonde) profiler. The parameters M, LT, and glat are approximated by trigonometric basis functions, while zO is described by a polynomial. A series of models were produced with different number of coefficients (number of terms) of the basis functions. Comparison between models revealed that those with larger number of coefficients can produce unrealistic extremes of the model curves due to the non-uniform sampling of data along the axes. Further considered is the simplest model approximating M, LT, and glat by simple 24 sinusoidal functions and linearly depending on zO. The model description and its 54 coefficients are given in Appendix 1 and can be used by other users for reconstruction of plasmasphere density profiles. The main variation of the ratio along geomagnetic latitude at fixed values of the other model parameters is illustrated in a series of plots.