Radar observations of the thermosphere

Abstract

Radar systems rely on backscatter echoes to determine range and Doppler shift of a target. In the upper-atmosphere, the target is charged particles, generally electrons, but these are strictly in the minority. In order to use a radar to observe the majority neutral atmosphere a new technique is developed. Using the ion-momentum equation in the ionosphere, simplified for magnetic field perpendicular (or parallel. ion motion only, we derive an expression for the ion-neutral collision frequency that depends primarily on the temporal and spatial variability of the ion velocity. Experiments performed by the EISCAT ionospheric modification facility (located in Norway. in 2015, 2016 and 2017, using the CUTLASS-Hankasalmi SuperDARN radar for observations, show that realistic estimates of thermospheric neutral density compared to the MSIS model can be obtained from the ion-neutral collision frequency in the thermosphere with an hourly cadence. Since HF radio wave propagation refracts in the upper-ionosphere (150-300 km altitude., a functional comparison is only possible with ray tracing. The new technique works well, at least for low geomagnetic activity. The purpose for developing this new technique is to monitor and study the thermospheric density variations, which may be as much as an order of magnitude, due to solar and geomagnetic storms. This affects, for example, satellite drag and therefore satellite lifetime with obvious economic impact. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.