Increase in the carbon dioxide infrared emissions during solar proton events

Increase in the nighttime high-latitude nonthermal emissions in the mesosphere and lower thermosphere in the 4.3 and 15 µm CO₂ bands during solar proton events has been estimated for the first time. The estimations have been performed for protons with energies not lower than 1 MeV precipitating into the atmosphere. A strong increase in the 4.3 µm emission can be anticipated during the above events; however, a substantial increase in the 15 µm emission is improbable. The 4.3 µm emission can increase only above approximately 80 km regardless of the energy of precipitating protons. The excitation of CO₂ vibrational states, transitions from which generate the 4.3 µm emission, is caused by the vibrational excitation of N₂ molecules due to collisions with secondary electrons, produced during solar proton events, and the following transfer of this excitation to CO₂(00⁰1) molecules during N₂-CO₂ collisions.