[M-SD35] Future Missions of Satellite Earth Observation

[MSD35-07] Satellite Mission for observation of water vapor isotope ratio using THz wavelengths

*Kei Yoshimura¹, Yasuko Kasai², Ryoichi Imasu³, Nawo Eguchi⁴ (1.Institute of Industrial Science, The University of Tokyo, 2.National Institute Of Information And Communications Technology, 3.Atmosphere and Ocean Research Institute, The University of Tokyo, 4.Research Institute for Applied Mechanics, Kyushu University)

Keywords:water vapor isotope ratio, THz wavelengths, precipitation efficiency, data assimilation

Water vapor isotope ratios (δ²H) have been used to understand atmospheric water cycle processes because of their clear sensitivity to water phase changes. Recently, it has been shown that observed water vapor isotope ratios can constrain the atmospheric water cycle process through data assimilation, and can contribute to improving the accuracy of atmospheric state analysis and weather forecasting. Nadir observations in the upper troposphere have not been conducted so far, although SCIAMACHY and GOSAT have investigated water vapor isotope ratios in the lower troposphere using near-infrared FTS, and TES and IASI have investigated water vapor isotope ratios in the mid troposphere using infrared FTS. This mission aims to observe water vapor isotope ratios in the upper troposphere using THz wavelengths to further understand the atmospheric water circulation process in detail, and to use the data for real-time observations to improve the accuracy of weather forecasting. The parameters observed during this mission are water vapor content [H₂O] and isotopic water vapor content [H²HO] at altitudes above 7 km. The isotopic ratio δ²H is obtained from [H²HO]/[H₂O]. The water vapor isotopic ratio in the upper troposphere is a good indicator of how much condensation has occurred in the upwelling in the tropopause cell, and together with the water vapor isotopic ratio in the lower middle troposphere, which is affected by isotopic fractionation due to re-evaporation from falling raindrops, the net rate of water vapor condensation and raindrop evaporation in the atmosphere, or precipitation efficiency, is estimated. The magnitude of the precipitation efficiency in the atmosphere has a significant impact on the atmospheric general circulation.