Long term analysis of thermospheric total mass density

In this thesis study, the long-term changes of thermospheric mass density obtained at altitudes of 250 km, 275 km, 325 km, 375 km, 400 km, 425 km, 475 km, 525 km, 550 km, 575 km were investigated. In addition, the relationship between mass density and sunspot number (SSN) was analyzed. The relationship between thermospheric mass density values for sunspot number and altitudes was investigated during the 20th, 21st, 22nd, 23rd and 24th solar cycles. In order to reveal the trends and cyclical components in the total mass density data in temporal analyses, single spectrum analysis (SSA) was performed. In addition, correlation coefficients between total mass density and SSN were determined for each altitude. According to the findings, a weak relationship was obtained between SSN and thermospheric mass density at altitudes of 250 km and 325 km in 1970 and 1975, while for all the remaining altitudes, only the correlation coefficient of 1975 was at its lowest value. A positive relationship was observed between total mass density and SSN values for all the examined years and altitudes except 1970 at altitudes of 250 km and 325 km. It was observed that the correlation coefficient increased with the increase in altitude in all the examined time periods. It is thought that this situation is due to the relationship between the angle of incidence of solar rays. In this study, it is seen that the thermospheric mass density has a long-term and high dependence on solar activity. It is thought that this situation will contribute to the development of thermospheric mass density models, which are of critical importance for GNSS systems, satellite orbit predictions, orbit entry times, in-orbit collision prediction and communication technologies.