Potential of Mid-tropospheric Water Vapor Isotopes to Improve Large-Scale Circulation and Weather Predictability

Recent satellite techniques have uncovered detailed tropospheric water vapor isotope patterns on a daily basis, yet the significance of water isotopes on weather forecasting has remained largely unknown. Here, we perform a proof‐of‐concept observing system simulation experiment to show that mid‐tropospheric water isotopes observed by the Infrared Atmospheric Sounding Interferometer (IASI) can substantially improve weather forecasts through non‐local impacts on the convective heating structure and large‐scale circulation. Assimilating IASI isotopes can improve wind, humidity, and temperature fields by more than 10% at mid‐troposphere compared to only assimilating conventional non‐isotopic observations. These improvements are about two‐thirds of assimilating simultaneous IASI water vapor observations. The improvements can be attributed more to thermodynamic (phase change) effects than dynamic (transport) effects of water isotopes. Furthermore, isotopic observations produce additional 3%–4% improvements to the fields constrained by the conventional observations and simultaneous IASI water vapor observations, demonstrating the unique characteristics of water isotopes.
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Plain Language Summary
Accurate weather forecasting has tremendous socio‐economic benefits by saving lives from natural hazards and affecting numerous sectors including water resources, energy, and agriculture. Although recent satellite techniques have enabled observing detailed water isotope patterns (e.g., HDΟ and Η$_{2}$$^{18}$O) in the atmosphere, it has not been incorporated in operational weather forecasting. Here, we show that water isotopes can substantially improve weather forecasts by improving the heating structure and large‐scale circulation. Satellite‐observed isotopes can improve wind, humidity, and temperature fields up to 3%–4% compared to utilizing conventional non‐isotopic observations and concurrent water vapor observations by the same satellite. We anticipate that our results will facilitate further modeling developments in isotopic processes and benefit the societal sectors by improving operational weather forecasting.