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

The Earth's upper atmosphere is under the total control of solar activity as the Earth is in the atmosphere of the Sun. 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 (<1% per decade) and statistically insignificant. Large and physically unreal $\text{Tn}=\text{Ti}$ trends obtained from ISR observations may be related to the routine ISR method. Solar and geomagnetic activities are two channels controling of foF1, foF2 and hmF2 long-term variations. Atomic oxygen, [O] and [O]/[N2] ratio control foF1 and foF2, while Tex controls the hmF2 long-term variations. A linear trend in (hmF2)11y estimated over the (1962–2010) period is small and insignificant. The foF2 and foF1 long-term variations demonstrate a negative trend over the (1962–2010) period. However it is not related to the CO2 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.

The Earth's upper atmosphere is under the total control of solar activity as the Earth is in the atmosphere of the Sun. 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 are small (<1% per decade) and statistically insignificant. Large and physically unreal trends obtained from ISR observations may be related to the routine ISR method. Solar and geomagnetic activities are two channels controling of f_oF₁, f_oF₂ and h_mF₂ long-term variations. Atomic oxygen, [O] and [O]/[N₂] ratio control f_oF₁ and f_oF₂, while Tex controls the h_mF₂ long-term variations. A linear trend in (h_mF₂)_11y estimated over the (1962–2010) period is small and insignificant. The f_oF₂ and f_oF₁ long-term variations demonstrate a negative trend over the (1962–2010) period. However it is not related to the CO₂ concentration increase but is due to [O] decrease after ∼ 1990. A close similarity between (foE)_11y and 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.