ION COMPOSITION MEASUREMENTS AND MODELING AT ALTITUDES FROM 140 TO 350 KM USING EISCAT MEASUREMENTS

This work aims at processing the data of CPI and CP2 programs of EISCA T ionospheric radar from 1987 to 1994 using the ''full profile'' metho d which allows to solve the ''temperature-composition'' ambiguity prob lem in the lower F region. The program of data analysis was developed in the CEPHAG in 1995-1996. To improve this program, we implemented an other analytical function to model the ion composition profile. This n ew function better reflects the real profile of the composition. Secon dly, we chose the best method to select the initial conditions for the ''full profile'' procedure. A statistical analysis of the results was made to obtain the averages of various parameters: electron concentra tion and temperature, ion temperature, composition and bulk velocity. The aim is to obtain models of the parameter behaviour defining the io n composition profiles : z(50) (transition altitude between atomic and molecular ions) and dz (width of the profile), for various seasons an d for high and low solar activities. These models are then compared to other models. To explain the principal features of parameters z(50) a nd dz, we made an analysis of the processes leading to composition cha nges and related them to production and electron density profile. A ne w experimental model of ion composition is now available.