Production of the Balmer H_β (blue line) and H_α (dashed red) emissions due to proton precipitation. For the sake of clarity, we choose a vertical Dirac distribution as the proton energy spectrum at 10 keV. The total energy is 5 erg. The green and red emissions of atomic oxygen are also shown, in their respective colour, to highlight that proton precipitation will lead to these emissions being the most important above 180 km altitude. Therefore, these cannot explain the current observation of blue emissions only.