The Changing-Atmosphere Infra-Red Tomography Explorer A candidate for ESA's Earth Explorer 11

To improve our knowledge of the coupling of atmospheric circulation, composition and regional climate change, and to provide the urgently needed observations of the on-going changes and processes involved, we have proposed the Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT), selected for Phase 0 as one of four candidates for Earth Explorer 11. There is growing evidence that the global atmosphere is changing throughout its entire depth from the surface to the fringes of space due to anthropogenic emissions of greenhouse gases, pollutants, aerosol precursors, and the recovery from ozone-depleting substances. Changes in atmospheric composition are closely coupled with changes in circulation and together affect surface climate, weather and air quality. CAIRT will be the first limb-sounder with imaging Fourier-transform infrared technology in space. By observing simultaneously the atmosphere from the troposphere to the lower thermosphere (about 5 to 115 km altitude), CAIRT will provide global observations of ozone, temperature, water vapour, as well as key halogen and nitrogen compounds. Observing nitrogen oxides from the stratosphere up to the lower thermosphere will help to better constrain the coupling with the upper atmosphere, solar variability and space weather. Observation of long-lived tracers (such as N2O, CH4, SF6, CF4) will provide information critical on transport, mixing and circulation changes. CAIRT will deliver essentially a complete budget of stratospheric sulfur (by observations of OCS, SO2, and H2SO4-aerosols), as well as observations of ammonia and ammonium nitrate aerosols. Biomass burning and other pollution plumes, and their impact on ozone chemistry in the UTLS region, will be detected from observations of HCN, CO and a further wealth of volatile organic compounds. The potential to measure water vapour isotopologues will help to constrain water vapour and cloud processes and interactions at the Earth's surface. The high-resolution measurements of temperature will provide the momentum flux, phase speed and direction of atmospheric gravity waves. CAIRT thus will provide comprehensive information on the driving of the large-scale circulation by different types of waves. Tomographic retrievals will provide temperature and trace gas profiles at a much higher horizontal resolution and coverage than achieved from space so far. Flying in loose formation with the Second Generation Meteorological Operational Satellite (MetOp-SG) will enable combined retrievals with observations by the New Generation Infrared Atmospheric Sounding Interferometer (IASI-NG) and Sentinel-5, resulting in consistent atmospheric profile information from the surface up to the lower thermosphere. Our presentation will give an overview of the proposed CAIRT mission, the science to be addressed and first results from the ongoing Phase 0 science study and campaign activities.