3D Distribution of Atmospheric Vapor Isotopes in East Asia: Vehicle-based Spatial and Seasonal In-situ Observations and Drone-based Tropospheric Vertical Profiles and Their Added Value to Infer Convective Processes and Paleoclimate Reconstruction
Authors: Wang Di , Risi Camille , Tian Lide 
Published: March 2024

&#160; &#160; Stable isotopic signals preserved in natural precipitation archives, such as ice cores, provide information on past climatic changes. When measured in the water vapor, water isotopes bear information on large-scale transport, convective and cloud processes.
&#160; &#160; To document spatial and seasonal variations across China, we made in-situ observations of near-surface vapor isotopes over a large region (over 10000 km) across China in both pre-monsoon and monsoon seasons, using a newly-designed vehicle-based vapor isotope monitoring system. We found that the observed spatial variations in both periods represent mainly seasonal-mean spatial variations, but are also influenced by synoptic-scale variations during the monsoon period. The spatial variations of vapor &#948;18O are mainly controlled by Rayleigh distillation along air mass trajectories during the pre-monsoon period, but are significantly influenced by different moisture sources, continental recycling processes and convection along moisture transport during the monsoon period. Thus, the North-South gradient observed during the pre-monsoon period is counteracted during the monsoon period. These results provide an overview of the spatial distribution and seasonal variability of water isotopic composition in East Asia and their controlling factors, and emphasize the need to interpret proxy records in the context of the regional system.
&#160; &#160; 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 observation 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 are derived for the first time. We find that the vertical profiles of water vapor isotopic composition reflects 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 &#948;18O&#160; 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 &#948;18O 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. The observed seasonal and intra-seasonal variations are generally vertically coherent, due to the strong vertical convective mixing and local convective detrainment of vapor originating from the low levels. The vapor is more depleted during the monsoon season and in October, due to deep convection along trajectories.