# 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

## TL;DR

This study develops advanced models to simulate halos and elves caused by lightning, analyzing their optical spectra and chemical impacts, and finds that these events produce significant localized NO but negligible global chemical effects.

## Contribution

The paper introduces upgraded two-dimensional models that calculate vibrationally detailed optical spectra of elves and quantify their chemical impacts, including the first detailed spectra for elves triggered by CIDs and EIPs.

## Key findings

- Optical spectra of elves are independent of lightning type.
- Single halos produce about 10^16 NO molecules per joule.
- Global NO production from halos and elves is negligible compared to tropospheric lightning.

## Abstract

Halos and elves are Transient Luminous Events (TLEs) 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 (CG) lightning discharges, Compact Intra-cloud Discharges (CIDs) and Energetic In-cloud Pulses (EIPs). 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 CIDs and EIPs. 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 one second. 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 atmopshere at $\sim10^{-7}$ Tg~N/y. This global chemical impact of halos and elves is seven orders of magnitude below the production of NO in the troposphere by lightning discharges.