Long-term Trends in Thermospheric and Ionospheric Parameters as the Reflection of Solar Activity Long-Term Variations

Abstract

TAbstsract2. Using retrieved thermospheric parameters from observed foF1 long-term variations in Tex and neutral composition have been revealed for the period of 5 solar cycles. The residual trends in Tex and $\rho$ are small ( $\text{Tn}=\text{Ti}$ trends obtained from ISR observations may be related to the routine ISR method. Solar and geomagnetic activities are two channels controling of f o F 1 , f o F 2 and h m F 2 long-term variations. Atomic oxygen, [O] and [O]/[N 2 ] ratio control f o F 1 and f o F 2 , while Tex controls the h m F 2 long-term variations. A linear trend in (h m F 2 ) 11y estimated over the (1962–2010) period is small and insignificant. The f o F 2 and f o F 1 long-term variations demonstrate a negative trend over the (1962–2010) period. However it is not related to the CO 2 concentration increase but is due to [O] decrease after ∼ 1990. A close similarity between (foE) 11y and $(\text{R}_{12})_{11\text{y}}(\text{c}.\text{c}. =0.996)$ tells us that the origin of these (foE) 11y variations is the Sun. The residual (foE) 11y trend is small (∼ 0.029% per decade) and insignificant. Thus (foE) 11y variations are totally dependent on variations of solar activity. The main conclusion – all revealed long-term variations of thermospheric and ionospheric parameters have a natural (not anthropogenic) origin related to long-term variations in solar activity.