Inferring thermospheric composition from ionogram profiles: a calibration with the TIMED spacecraft
Abstract 
\textlessp\textgreater\textlessstrong class="journalcontentHeaderColor"\textgreaterAbstract.\textless/strong\textgreater We present a method for augmenting spacecraft measurements of thermospheric composition with quantitative estimates of daytime thermospheric composition below 200 \textlessspan class="inlineformula"\textgreaterkm\textless/span\textgreater, inferred from ionospheric data, for which there is a global network of groundbased stations. Measurements of thermospheric composition via groundbased instrumentation are challenging to make, and so details about this important region of the upper atmosphere are currently sparse. The visibility of the F1 peak in ionospheric soundings from groundbased instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the “\textlessspan class="inlineformula"\textgreater\textitG\textless/span\textgreater” factor, a function of ion production rate and loss rates via ion–atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the \textlessspan class="inlineformula"\textgreater\textitG\textless/span\textgreater factor obtained from ionograms recorded at Kwajalein (9\textlessspan class="inlineformula"\textgreater$^\textrm∘$\textless/span\textgreater N, 167.2\textlessspan class="inlineformula"\textgreater$^\textrm∘$\textless/span\textgreater E) for 25 times during which the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft recorded approximately colocated measurements of the neutral thermosphere. We find a linear relationship between \textlessspan class="inlineformula"\textgreater\textlessmath xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"\textgreater\textlessmsqrt\textgreater\textlessmi\textgreaterG\textless/mi\textgreater\textless/msqrt\textgreater\textless/math\textgreater\textlessspan\textgreater\textlesssvg:svg xmlns:svg="http://www.w3.org/2000/svg" width="21pt" height="12pt" class="svgformula" dspmath="mathimg" md5hash="fe020e378fd223a5491b91deb815e309"\textgreater\textlesssvg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="angeo393092021ie00001.svg" width="21pt" height="12pt" src="angeo393092021ie00001.png"/\textgreater\textless/svg:svg\textgreater\textless/span\textgreater\textless/span\textgreater and the moleculartoatomic composition ratio, with a gradient of \textlessspan class="inlineformula"\textgreater2.55±0.40\textless/span\textgreater. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be \textlessspan class="inlineformula"\textgreater4.75±0.4\textless/span\textgreater. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of \textlessspan class="inlineformula"\textgreater4.20±0.8\textless/span\textgreater. This relationship has potential for using groundbased ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere via a relatively simple model. This has applications in understanding longterm change and the efficacy of the upper atmosphere on satellite drag.\textless/p\textgreater

Year of Publication 
2021

Journal 
Annales Geophysicae

Volume 
39

Number of Pages 
309319

Date Published 
mar

ISSN Number 
09927689

URL 
https://angeo.copernicus.org/articles/39/309/2021/

DOI 
10.5194/angeo393092021
