Estimating thermospheric neutral densities using ISR-observations during active HF-radio wave ionospheric heating experiment

Abstract

In this study we present a method to estimate neutral thermospheric densities using ISR-observations following a sequence of high-frequency radio wave ionospheric heating modi cations in the vicinity of the ionosphere peak density altitude (hmF2), and the results from two different days of observations with low geomagnetic activity levels (AP<4) that are compared to the MSIS model.

Slight discrepancies between the estimated neutral thermospheric densities and the MSIS model was found for the 18th of October, where the total density was a factor 0:98±0:02 of MSIS at the hmF2, with increasing deviations at higher altitudes, ending at a factor 0:94 ± 0:04 at 300 km. The main thermospheric neutral constituents, O, N2 and O2 were estimated to a factor 1:05 ± 0:03, 0:950 ± 0:002 and 0:73 ± 0:03 of the MSIS modelled constituents at hmF2, respectively, with all factors slightly decreasing with altitude. The 15th of August achieved less electron heating at hmF2 due to a widespread electron content and high absorption in the E and D regions, and had significantly more noise making the standard errors in the estimates far exceed a reasonable density for quiet geomagnetic activities, at a factor 0:98 ± 0:37 of MSIS, making the result from the 15th of August inconclusive.

The findings from the observations has shown that this method can if observation-data from several individual heating-cycles are used extract the neutral thermospheric densities within reasonable certainty, if the thermospheric-ionospheric condition allow for repeated measurements.