Highlights F10.7 cannot describe the hmF2 behavior in the 24th SA cycle. hmF2 behaves during the “vague” period similarly to foF2. The reduction of atomic oxygen in the thermosphere is concluded.
Abstract The measurements of the F2-layer height, hmF2, at Juliusruh station during 1958–2018 are analyzed by the method developed by the authors earlier and used to determine long-term trends in parameters of the F2 layer. It is found that, in the same way as for the behavior of the critical frequency described by the authors in the previous publication, peculiarities in the hmF2 behavior are observed after 2002–2003. If the solar activity index F10.7 is used, an increase in the ΔhmF2 value is observed and provides a positive trend in hmF2 that contradicts to the available ideas on the continuing process of cooling and contraction of the upper atmosphere. If the F10.7 index corrected by other SA indices (the sunspot number Rz or the Lyman-alpha line intensity) is used, as it has been done for the foF2 trends in the previous publications by the authors, the picture of changes in the hmF2 trends is obtained similarly to the changes in the foF2 trends. A well pronounced negative trend in hmF2 is observed to 2002–2003, and then it is substituted by a chaotic change in ΔhmF2 during the “vague” period, whereas during the last analyzed years it becomes negative again. Analysis of the slope s of the foF2(hmF2) dependence shows that there is a systematic decrease in s with time. That confirms the conclusion of the authors on a decrease in the oxygen amount in the thermosphere.
Trends in hmF2 and the 24th solar activity cycle
Advances in Space Research ; 66 , 2 ; 292-298
2020-04-08
7 pages
Article (Journal)
Electronic Resource
English
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