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Abstract

Stable isotopic signals preserved in natural precipitation archives, such as ice cores, provide information on past climatic changes. When measured in water vapor, water isotopes bear information on large-scale transport, and convective and cloud processes. To better understand the physical processes that control the vertical distribution of vapor isotopes and the added value of vapor isotopic measurements to infer deep convective processes, we made observations of the vertical profiles of atmosphere vapor isotopes up to the upper troposphere (from the ground surface at 3856m up to 11000m a.s.l.) from June to October in the southeastern Tibetan Plateau using a specially-designed unmanned-aerial-vehicle system. The vertical distribution of atmospheric water vapor isotopes across the entire monsoon period up to the upper troposphere is derived for the first time. We find that the vertical profiles of water vapor isotopic composition reflect a combination of large-scale processes, in particular deep convection along trajectories, and local convective processes, in particular convective detrainment and sublimation of ice crystals. The observed vapor δ¹⁸O decreases and its d-excess increases with altitude up to 8-10km, consistent with the progressive condensation of water vapor and precipitation. Beyond this altitude, where the maximum convective detrainment occurs, the vapor δ¹⁸O re-increases with altitude, reflecting the sublimation of ice crystals detrained from convective clouds. The d-excess is maximum during the monsoon period, due to more depleted initial vapor.