Kwagala, N. K., K. Oksavik, D. A. Lorentzen, M. G. Johnsen, and K. M. Laundal (2018), Seasonal and Solar Cycle Variations of Thermally Excited 630.0 nm Emissions in the Polar Ionosphere, J. Geophys. Res. Space Phys., 123, doi.org/10.1029/2018JA025477 (pdf)