Research Article

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

¹ Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via di Vigna Murata 605, Roma 00143, Italy
² Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow 142190, Russia

^* Corresponding author: loredana.perrone@ingv.it

Received: 15 September 2016
Accepted: 13 August 2017

Abstract

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_oF₁ neutral composition (O, O₂, N₂), exospheric temperature, Tex and the total solar EUV flux with λ < 1050 Å; 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]/[N₂] ratio control f_oF₁ and f_oF₂ while neutral temperature, Tex controls h_mF₂ long-term variations. Noontime f_oF₂ and f_oF₁ long-term variations demonstrate a negative linear trend estimated over the (1962–2010) period which is mainly due to atomic oxygen decrease after ∼1990. A linear trend in (δh_mF₂)_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, ρ 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 ∼5 solar cycles (1957–2015) are very small (<0.5% per decade) and statistically insignificant.