CHIMTEA - Chemical Impact of Thunderstorms on Earth's Atmosphere

Since their accidental discovery in the 1990s, lightning-related sprites, other transient luminous events (TLEs), and terrestrial gamma-ray flashes have shown us how the impact of thunderstorms extends from the troposphere up to the upper atmosphere and ionosphere. Thunderstorms are a key player for the climate system, in particular through lightning-produced NOx and troposphere–stratosphere exchange. The CHemical Impact of Thunderstorms on Earth’s Atmosphere (CHIMTEA) project focused on TLE-producing thunderstorms and their possible impact on stratospheric NOx and ozone. The distribution and seasonal cycle of thunderstorm activity were studied through global lightning data and TLE observations over Europe. Michelson Interferometer for Passive Atmosphere Sounding (MIPAS)/Environmental Satellite (ENVISAT) measurements of NOx, ozone, and other related constituents from the upper troposphere to the mesosphere were analyzed with a 2D tomographic approach to quantify thunderstorm-induced changes and explore how to improve their detectability. The study included observations from Global Ozone Monitoring by Occultation of Stars (GOMOS)/ENVISAT, other satellites, and in situ measurements. The sensitivity of the measurements to sprite-NOx was investigated through ad hoc radiative transfer simulations quantifying reference thresholds. Global and regional observations showed sprite-NOx to be at the edge of current detectability, with no detectable impact on ozone. Model simulations were performed including for the first time a sprite-NOx parameterization in the Whole Atmosphere Community Climate Model (WACCM): it was shown that sprites may contribute significantly to tropical NOx in the middle mesosphere and reach detectable levels above particularly active thunderstorms. Extension of the adopted strategy to study lightning-NOx was recommended, whereas the modeling and multi-satellite approach was shown to be suitable in support to the upcoming space missions.