Wednesday

The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of the thermospheric composition. The shape of the ionospheric profile in the transition region between F1 and F2 peaks can be expressed in terms of the ‘G’ factor, a function of ion production rate and loss rates via atomic and molecular processes. This in turn can be expressed as the square of the ratio of ions lost via molecular and atomic processes. We present a comparison of the G factor obtained from ionograms recorded at Kwajalein (9 N, 167.2 E) for 25 events during which the
TIMED spacecraft was making co-located measurements of the neutral thermosphere. An estimate is made of the relationship between √G and the molecular: atomic composition ratio. A linear relationship is found. Scatter within this relationship will be due to the assumptions used and the fact that the two measurements are not truly simultaneous (being made 15 minutes and 5 degrees in latitude and longitude from each other). Nevertheless, this relationship reveals the potential for using ground-based ionospheric measurements to infer variations in
the composition of the neutral thermosphere. Such information can be used to investigate spatial and temporal variations in thermospheric composition which 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.