Optical observations of thunderstorms from the International Space Station: recent results and perspectives

Kurzfassung

Thunderstorms develop primarily at low- and mid-latitudes, where the solar energy input is the largest. The atmosphere over land is heated unequally depending on the underlying surface, and thermal bubbles develop1. Some may rise as deep convection to the upper tropopause, occasionally even into the lower stratosphere2. Deep convection carries high amounts of water vapour, dust, aerosols, and trace gases from the polluted boundary layer that may reside at high altitudes for times much longer than the duration of the storm (days versus hours). Spreading over extended regions (~100–1000 km), they perturb the radiative properties of the upper troposphere and lower stratosphere (UTLS) region3–5. Lightning affects trace species’ concentrations by specific chemical reactions in the heated lightning channel6–8. It can cause deaths and injuries, crop and property damage, and may ignite wildfires9 that release huge quantities of trace species (including greenhouse gases) into the atmosphere. Locally and temporally these amounts might exceed anthropogenic emission of such gases10. The emissions may be injected into the stratosphere11,12 and are important contributors to global warming and climate change13. Concurrently, climate change increases the frequency of hot and dry weather situations that fuel wildfires. Studies on lightning activity in a warmer climate suggest that the average global activity may decrease because of a diminishing amount of hail in thunderstorms14, whereas regional activities may increase15,16. Especially in the high Arctic region, where wildfires are easily induced, a drastic rise in lightning activity has been observed17, causing a rapid release of trace species with limited possibilities to quench the fires. For these reasons, the World Meteorological Organisation included lightning as an essential climate variable18. It is of interest, then, to understand how thunderstorms and lightning activity, on the one hand, affect the climate balance and, on the other hand, how they are affected by a changing climate. Here, the ISS is in a well-suited orbit, passing over all the major thunderstorm regions of the Earth within ±51.6° latitude, as shown in Fig. 1. In the following, we give a brief account of the development of optical observations of lightning activity from space. We discuss some aspects of how thunderstorms may affect the radiative properties of the atmosphere and point out that the altitude of perturbations to atmosphere of greenhouse gases is important. We end by discussing the opportunities for using the ISS, or another platform in LEO, for future observations with slanted viewing geometry that allows for measurements of thunderstorm activity with resolution in altitude, complementing the primarily