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 NO_x 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 NO_x 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 NO_x, 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-NO_x was investigated through ad hoc radiative transfer simulations quantifying reference thresholds. Global and regional observations showed sprite-NO_x 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-NO_x parameterization in the Whole Atmosphere Community Climate Model (WACCM): it was shown that sprites may contribute significantly to tropical NO_x in the middle mesosphere and reach detectable levels above particularly active thunderstorms. Extension of the adopted strategy to study lightning-NO_x was recommended, whereas the modeling and multi-satellite approach was shown to be suitable in support to the upcoming space missions.