Long-Term Variations of June Column Atomic Oxygen Abundance in the Upper Atmosphere Inferred From Ionospheric Observations

For the first time, atomic oxygen column content [O](col) has been inferred from June daytime monthly median f(0)F(1) and f(0)F(2) observations at Rome, Juliusruh, Sodankyla, and Boulder to analyze its long-term variations for the period of similar to 6 solar cycles. The analysis is interesting in the light of possible anthropogenic impact on the upper atmosphere. After the removal of solar and geomagnetic activity effects from the inferred [O](col) variations, the residual linear trends are negative and statistically insignificant at middle latitudes. It is shown that similar to 93% (the corresponding correlation coefficient is 0.964 +/- 0.03) of the whole [O](col) variability is explained by solar and geomagnetic activity long-term variations and only similar to 7% may be attributed to other processes (reasons) including the anthropogenic impact. Solar and geomagnetic activity contributions to [O](col) long-term variations decrease with time, and this may be related to the low solar activity epoch, which we have entered. The main conclusion is that the long-term variations of the atomic oxygen column content inferred from ionospheric observations are due to solar and geomagnetic activity; that is, they have a natural origin.