Modeling the Chemical Impact and the Optical Emissions Produced by Lightning-Induced Electromagnetic Fields in the Upper Atmosphere: The case of Halos and Elves Triggered by Different Lightning Discharges

Halos and elves are transient luminous events produced in the lower Ionosphere as a consequence of lightning-driven electromagnetic fields. These events can influence the upper atmospheric chemistry and produce optical emissions. We have developed different two-dimensional self-consistent models that couple electrodynamical equations with a chemical scheme to simulate halos and elves produced by vertical cloud-to-ground lightning discharges, compact intracloud discharges and energetic in-cloud pulses. The optical emissions from radiative relaxation of excited states of molecular and atomic nitrogen and oxygen have been calculated. We have upgraded previous local models of halos and elves to calculate for the first time the vibrationally detailed optical spectra of elves triggered by compact intracloud discharges and energetic in-cloud pulses. According to our results, the optical spectra of elves do not depend on the type of parent lightning discharge. Finally, we have quantified the local chemical impact in the upper atmosphere of single halos and elves. In the case of the halo, we follow the cascade of chemical reactions triggered by the lightning-produced electric field during a long-time simulation of up to 1 s. We obtain a production rate of NO molecules by single halos and elves of 10(16) and 10(14) molecules/J, respectively. The results of these local models have been used to estimate the global production of NO by halos and elves in the upper atmosphere at similar to 10(-7) Tg N/year. This global chemical impact of halos and elves is 7 orders of magnitude below the production of NO in the troposphere by lightning discharges. Plain Language Summary Lightning discharges can trigger transient luminous events in the mesosphere. Halos and elves, two types of transient luminous events, are seen as red colored discs or rings at altitudes between 70 and 90 km. These luminous events are a consequence of a cascade of chemical reactions triggered by the lightning-produced electromagnetic field. In this paper, we develop two self-consistent models to investigate the inception and evolution of halos and elves produced by different types of lightning discharges. These models allow us to quantify the predicted chemical impact of halos and elves in the mesosphere as well as to predict their rovibrational optical spectra. Finally, we estimate the global production of NO by these events.