Long-term variations of the upper atmosphere parameters on Rome ionosonde observations and their interpretation

A recently proposed self-consistent approach to the analysis of thermospheric and ionospheric long-term trends has been applied to Rome ionosonde summer noontime observations for the (1957-2015) period. This approach includes: (i) a method to extract ionospheric parameter long-term variations; (ii) a method to retrieve from observed f(o)F(1) neutral composition (O, O-2, N-2), exospheric temperature, Tex and the total solar EUV flux with lambda < 1050 angstrom; and (iii) a combined analysis of the ionospheric and thermospheric parameter long-term variations using the theory of ionospheric F-layer formation. Atomic oxygen, [O] and [O]/[N-2] ratio control f(o)F(1) and f(o)F(2) while neutral temperature, Tex controls h(m)F(2) long-term variations. Noontime f(o)F(2) and f(o)F(1) long-term variations demonstrate a negative linear trend estimated over the (1962-2010) period which is mainly due to atomic oxygen decrease after similar to 1990. A linear trend in (delta h(m)F(2))(11y) estimated over the (1962-2010) period is very small and insignificant reflecting the absence of any significant trend in neutral temperature. The retrieved neutral gas density, rho atomic oxygen, [O] and exospheric temperature, Tex long-term variations are controlled by solar and geomagnetic activity, i.e. they have a natural origin. The residual trends estimated over the period of similar to 5 solar cycles (1957-2015) are very small (<0.5% per decade) and statistically.