How often do thermally excited 630.0 nm emissions occur in the polar ionosphere?
The first ever statistical investigation of the contribution from thermally excited atomic oxygen emissions (630.0 nm red aurora) confirms its importance in the dayside polar and cusp ionosphere. More than 400,000 measurements from the EISCAT Svalbard radar over a 15 year period (2000-2015) are included in the study. Strong thermal emission is found to be most likely around Noon local time and associated with high electron temperatures and nominal electron densities, in agreement with theoretical predictions. However, strong thermal emission is also found to occur at lower temperature and slightly enhanced electron density. This surprising result seems to be related to enhanced neutral atomic oxygen density indicative of neutral upwelling.
Shown are distributions of densities associated with strong (> 1 kR) and weak (< 1 kR) thermally excited emissions at different electron temperatures for electron (a,c) and modeled neutral atomic oxygen densities (b,d).
Kwagala, N. K., Oksavik, K., Lorentzen, D. A., and Johnsen, M. G. (2017). How often do thermally excited 630.0 nm emissions occur in the polar ionosphere? J. Geophys. Res.: Space Physics, 122. https://doi.org/10.1002/2017JA024744