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Inferring thermospheric composition from ionogram profiles: a calibration with the TIMED spacecraft

\textlessp\textgreater\textlessstrong class="journal-contentHeaderColor"\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="inline-formula"\textgreaterkm\textless/span\textgreater, inferred from ionospheric data, for which there is a global network of ground-based stations. Measurements of thermospheric composition via ground-based 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 ground-based 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="inline-formula"\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="inline-formula"\textgreater\textitG\textless/span\textgreater factor obtained from ionograms recorded at Kwajalein (9\textlessspan class="inline-formula"\textgreater$^\textrm∘$\textless/span\textgreater N, 167.2\textlessspan class="inline-formula"\textgreater$^\textrm∘$\textless/span\textgreater E) for 25 times during which the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between \textlessspan class="inline-formula"\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="svg-formula" dspmath="mathimg" md5hash="fe020e378fd223a5491b91deb815e309"\textgreater\textlesssvg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="angeo-39-309-2021-ie00001.svg" width="21pt" height="12pt" src="angeo-39-309-2021-ie00001.png"/\textgreater\textless/svg:svg\textgreater\textless/span\textgreater\textless/span\textgreater and the molecular-to-atomic composition ratio, with a gradient of \textlessspan class="inline-formula"\textgreater2.55±0.40\textless/span\textgreater. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be \textlessspan class="inline-formula"\textgreater4.75±0.4\textless/span\textgreater. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of \textlessspan class="inline-formula"\textgreater4.20±0.8\textless/span\textgreater. This relationship has potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere via a relatively simple model. This has applications in understanding long-term change and the efficacy of the upper atmosphere on satellite drag.\textless/p\textgreater

Scott, Christopher; Jones, Shannon; Barnard, Luke;

Published by: Annales Geophysicae      Published on: mar

YEAR: 2021     DOI: 10.5194/angeo-39-309-2021

Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect

We use the \textlessi\textgreateram\textlessi/\textgreater, \textlessi\textgreateran, as\textlessi/\textgreater and the \textlessi\textgreateraσ\textlessi/\textgreater geomagnetic indices to the explore a previously overlooked factor in magnetospheric electrodynamics, namely the inductive effect of diurnal motions of the Earth’s magnetic poles toward and away from the Sun caused by Earth’s rotation. Because the offset of the (eccentric dipole) geomagnetic pole from the rotational axis is roughly twice as large in the southern hemisphere compared to the northern, the effects there are predicted to be roughly twice the amplitude of those in the northern hemisphere. Hemispheric differences have previously been discussed in terms of polar ionospheric conductivities generated by solar photoionization, effects which we allow for by looking at the dipole tilt effect on the time-of-year variations of the indices. The electric field induced in a geocentric frame is shown to also be a significant factor and gives a modulation of the voltage applied by the solar wind flow in the southern hemisphere that is typically a ±30\% diurnal modulation for disturbed intervals rising to ±76\% in quiet times. For the northern hemisphere these are 15\% and 38\% modulations. Motion away from/towards the Sun reduces/enhances the directly-driven ionospheric voltages and reduces/enhances the magnetic energy stored in the tail and we estimate that approximately 10\% of the effect appears in directly driven ionospheric voltages and 90\% in changes of the rate of energy storage or release in the near-Earth tail. The hemispheric asymmetry in the geomagnetic pole offsets from the rotational axis is shown to be the dominant factor in driving Universal Time (\textlessi\textgreaterUT\textlessi/\textgreater) variations and hemispheric differences in geomagnetic activity. Combined with the effect of solar wind dynamic pressure and dipole tilt on the pressure balance in the near-Earth tail, the effect provides an excellent explanation of how the observed Russell-McPherron pattern with time-of-year \textlessi\textgreaterF\textlessi/\textgreater and \textlessi\textgreaterUT\textlessi/\textgreater in the driving power input into the magnetosphere is converted into the equinoctial \textlessi\textgreaterF\textlessi/\textgreater-\textlessi\textgreaterUT\textlessi/\textgreater pattern in average geomagnetic activity (after correction is made for dipole tilt effects on ionospheric conductivity), added to a pronounced \textlessi\textgreaterUT\textlessi/\textgreater variation with minimum at 02–10 UT. In addition, we show that the predicted and observed \textlessi\textgreaterUT\textlessi/\textgreater variations in average geomagnetic activity has implications for the occurrence of the largest events that also show the nett \textlessi\textgreaterUT\textlessi/\textgreater variation.

Lockwood, Mike; Haines, Carl; Barnard, Luke; Owens, Mathew; Scott, Chris; Chambodut, Aude; McWilliams, Kathryn;

Published by: Journal of Space Weather and Space Climate      Published on:

YEAR: 2021     DOI: 10.1051/swsc/2020077

Inferring thermospheric composition from ionogram profiles: A calibration with the TIMED spacecraft

Measurements of thermospheric composition via ground-based instrumentation are challenging to make and so details about this important region of the upper atmosphere are currently sparse. We present a technique thatdeducesquantitative estimates of thermospheric composition from ionospheric data, for which there is a global network of stations. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed bythe \textquoteleftG\textquoteright factor, a function of ion production rate and loss rates via ion-atom interchange reactionsand 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 estimatesof the G factor obtained from ionograms recorded at Kwajalein (9oN, 167.2oE) for 25 times during which theTIMED spacecraftrecordedapproximately co-located measurements of the neutral thermosphere.We find alinear relationship between √G and the molecular: atomic composition ratio,with agradient of 2.23 \textpm0.17 and an offset of 1.66 \textpm 0.19. This relationship reveals the potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere. Such information can be used to investigate spatial and temporal variations in thermospheric compositionwhich in turn has applications such as understanding the response of thermospheric composition to climate change and the efficacy of the upper atmosphere on satellite drag.

Scott, Christopher; Jones, Shannon; Barnard, Luke;

Published by: Annales Geophysicae Discussions      Published on: 03/2019

YEAR: 2019     DOI: 10.5194/angeo-2019-4710.5194/angeo-2019-47-RC110.5194/angeo-2019-47-RC2