We present a method for augmenting spacecraft measurements of thermospheric composition with quantitative estimates of daytime thermospheric composition below 200 km, 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 “G” 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 G factor obtained from ionograms recorded at Kwajalein (9^∘ N, 167.2^∘ 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 $\sqrt{G}$ and the molecular-to-atomic composition ratio, with a gradient of 2.55±0.40. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be 4.75±0.4. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of 4.20±0.8. 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.

中文翻译：

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从电离图轮廓推断热层组成：使用TIMED航天器进行校准

我们提出了一种方法，可通过对电离层数据推断出的200 km以下日间热层组成进行定量估算，从而增加对热层组成的航天器测量 ，为此，全球地面站网已建立。通过地面仪器对热层成分进行测量具有挑战性，因此目前稀少了有关高层大气这一重要区域的详细信息。来自地面仪器的电离层探测中F1峰的可见性是热层组成的敏感函数。F1和F2峰之间的过渡区域中的电离层轮廓可以表示为“ G”因子，是通过离子-原子交换反应和分子离子的解离重组产生的离子产生速率和损失速率的函数。这又可以表示为通过这些过程损失的离子比率的平方。我们比较了在夸贾林（^9∘N  ，^167.2∘E  ）处记录的25次电离图所获得的G因子的估计值，在此期间热球，电离层，中层，能量和动力学（TIMED）航天器记录了中性点大致位于同一地点的测量热球。我们发现$\sqrt{G}$分子与原子的组成比为2.55±0.40。或者，使用通过电离图反演获得的hmF1值，发现该梯度为4.75±0.4。此外，考虑到分子和原子种类中的相等电离，产生了4.20±0.8的梯度。这种关系具有使用基于地面的电离层测量值来通过相对简单的模型推断中性热层组成定量变化的潜力。这可用于了解长期变化以及高层大气对卫星阻力的影响。