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The Regional TEC Model Developed in Graz — A Progress Report

Feichter, E. / Leitinger, R.

Abstract In the frame of PRIME (Prediction and Retrospective Ionospheric Modeling over Europe) a regional TEC model has been developed from data gained by the Differential Doppler effect on the 150/400 MHz signals of the polar orbiting NNSS satellites. The model uses 4 sets of 5 × 5 Fourier coefficients, 2 sets for high solar activity (HSA), 2 for low solar activity (LSA). In each case one set is valid for 52.5°N, the other gives the latitudinal gradients. The Fourier terms represent the seasonal and local time mean (time independent term), the annual, the semi-annual, the diurnal, the semi-diurnal components and the combinations of annual and diurnal variation. The model was adopted by the PRIME project. Various combinations of Differential Doppler with Faraday data were tested too, the Faraday data were used to improve the diurnal variation in the models. Since differences in the TEC behaviour were found between odd and even solar cycles, two different regional models, one for odd, the other for even cycles, have been constructed. The differences concern the vernal-autumnal asymmetry around noon time: in the even cycles TEC was higher in spring than in autumn, the odd cycles showed the opposite (autumnal maxima).