Simulations of OH nightglow emission in the occurrence of sprites

Recent observations on sprites have revealed that the electron energies in the luminous lightning discharge channels above thundercloud tops could be in the range of a few electron volts. Sprites are transient luminous flashes, and each flash lasts from a few to tens of milliseconds. Because some chemical reaction rates are highly dependent on temperature, it is speculated that sprites might have a significant effect on the chemistry of the atmosphere. This study is aimed to investigate how OH nightglow emission in the MLT region is affected when sprites occur. Simulations of OH nightglow emission at temperatures of ∼200 K and 400 K were performed; the former represents the normal temperature in the absence of sprites, while the latter is the assumed temperature when sprites occur. The simulation results, ignoring dynamical effects, indicate that the number density of atomic O in the nightglow region is not very sensitive to a higher temperature but that of HO₂ and O₃ is reduced by 45% and 0.5%, respectively, while the production of OH is enhanced by a factor of 2.6. The column-integrated OH brightness shows a significant 16% increase when the temperature is at 400 K. The study indicates that sprites should produce a measurable effect on the OH brightness in the mesosphere.