The Need for a New Comprehensive View of the Middle Atmosphere–The Potential of Infrared Limb-Imaging Tomography

Earth’s middle atmosphere spans the deep region from the upper troposphere/lower stratosphere at around 10-km altitude to the mesosphere/lower thermosphere at around 100-km altitude. It is being increasingly recognized for its role in driving extreme surface weather and regional climate change. Climate models predict large ongoing and future changes in the middle atmosphere composition and circulation. However, the observations needed to detect, attribute, and understand these changes and their impacts, to test predictions, and thereby to improve our models, are lacking. Here, we show the capacity of infrared limb-imaging tomography to provide the needed observations. This evaluation is based on studies performed within a recent satellite mission concept—the Changing-Atmosphere Infrared Tomography Explorer (CAIRT). Observing thermal infrared emissions simultaneously from the midtroposphere at about 4 km up to the lower thermosphere at about 115-km altitude, this technique provides observations of temperature and an extensive range of trace gases with unprecedented spatial resolution of about 50 km × 50 km horizontally and about 1 km vertically. We show how these observations would (i) help to quantify the changing atmospheric circulation, (ii) allow characterization and quantification of the gravity waves that are critical in driving this circulation, (iii) reveal how variability in solar radiation and energetic particles propagate downward to affect regional climate at the surface, (iv) detect how volcanic eruptions and wildfires impact the middle atmosphere and climate, and (v) resolve how stratosphere–troposphere exchange affects ozone and water vapor in the crucial and climate-relevant tropopause region. Significance Statement The middle atmosphere serves as a critical link between Earth’s surface, the upper atmosphere, and the near-Earth space environment. It is increasingly influenced by rising greenhouse gas concentrations, ozone layer recovery, biomass burning emissions, and spacecraft activities, pushing the system into uncharted territory. However, current observational capabilities are insufficient to address these emerging challenges, with an imminent “data desert” of middle atmosphere observations. We show with the proposed Changing-Atmosphere Infrared Tomography Explorer (CAIRT) how infrared limb imaging can provide the urgently needed information on atmospheric waves, circulation patterns, and composition in a changing climate.