D-layer electron temperature estimates from Heater-modulated PMSE as observed by the IRIS riometer

Routledge, G., Kosch, M. J. and Honary, F.

Lancaster University, Lancaster, UK

HF pumping of the ionosphere causes the electron temperature in the D-layer to rise, which increases electron diffusivity and therefore modulates the polar mesospheric echoes (PMSE), as seen in the VHF radar, virtually destroying them. It is thought that the heated electrons attach themselves to the dust and/or aerosol particles within the PMSE. The IRIS riometer is sensitive to the free electron density and electron collision frequency, which is temperature dependent. Despite pump-induced changes in both these parameters in the D-layer, the riometer, in this case study, detects no significant change in the background absorption. This suggests that the absorption increase due to electron temperature increasing is cancelled out by the absorption decrease due to electron density decreasing. The increase in electron temperature in the D-layer has never been measured directly. We use the riometer observation, in conjunction with the VHF radar data of electron density and absorption models, to estimate the pump-enhanced electron temperature within the D-layer.