Moraitis, G.

2000-01, Belehaki, A., Moraitis, G., Tsagouri, I., Belehaki, A.; National Observatory of Athens, Institute for Space Applications and Remote Sensing, Palea Penteli, Greece, Moraitis, G.; National Observatory of Athens, Institute for Space Applications and Remote Sensing, Palea Penteli, Greece, Tsagouri, I.; University of Athens, Physics Department, Nuclear and Particle Physics Section, Athens, Greece, National Observatory of Athens, Institute for Space Applications and Remote Sensing, Palea Penteli, Greece, National Observatory of Athens, Institute for Space Applications and Remote Sensing, Palea Penteli, Greece, University of Athens, Physics Department, Nuclear and Particle Physics Section, Athens, Greece

In this paper an hourly local ionospheric index f n F 2 is proposed to define the normal level of the undisturbed ionosphere. For the determination of this index a model is developed where the normal values of the f 0 F 2 parameter were reproduced using multiple regression analysis. For each month of the year, for a given station, a set of 48 or 72 coefficients are calculated, depending on the monthly sunspot activity. Then, the normal values of the f 0 F 2 parameter are computed as a function of the daily sunspot number. The analysis of the model results revealed the following characteristics for the f n F 2 index: first, the temporal variations that characterize the normal ionosphere, imposing some artificial effects on the monthly median values, are eliminated from the newly derived f n F 2 index. Second, the f n F 2 index does not follow the false steplike variations observed in the monthly median f 0 F 2 time series, in transition periods from one month to another. Third, during intervals of low magnetospheric activity,the f n F 2 index presents a very good degree of fit with the observed f 0 F 2 parameter, compared to the monthly median f 0 F 2 behaviour. During disturbed conditions, the f n F 2 index remains at the normal level, whereas median values are affected by ionospheric disturbances. In general, the data analysis showed that the f n F 2 index varies only with the daily sunspot number Rz and is independent of the magnetospheric activity, approaching the level of the normal ionosphere with a high degree of confidence.