Modelling water pathways and isotopes in the trade-wind boundary layer (MoWITrade)
Final Report Abstract
The atmospheric water cycle in the marine trade-wind region is very important for the earth’s radiation budget and climate sensitivity. However, its representation in climate models is associated with large uncertainties, and it is thus important to better understand the transport processes shaping the water cycle in this critical region. In this project, these transport processes were investigated with the help of numerical simulations with a regional atmospheric model in a high-resolution, convection-permitting setup that explicitly quantifies water transport through numerical tracers and, in addition, also simulates the isotopic composition of atmospheric moisture allowing for a direct comparison with observations. We specifically focused on the free-tropospheric moisture content that is characterized by large variability on daily time scales and has important longwave radiative effects. A comparison with observations from the EUREC4A campaign shows that our simulations, in spite of a cold and dry bias associated with overly depleted isotope ratios below clouds and too enriched values at higher altitudes, captures the temporal variability of water isotopes reasonably well and can thus be used for a process-based analysis of the relationship between transport and isotopic variability. The moisture tracers indicate that our target region above Barbados is characterized by alternating large-scale circulation regimes with differing humidity and isotope signatures. Moist conditions are linked to water transport from the south, east, southeast and evaporation from the North Atlantic, whereas dry conditions correspond to transport from the extratropics in northerly and westerly flow. Based on a statistical model that links the moisture source contributions obtained from the numerical tracers to local conditions in the target region, we showed that water isotopes contain unique information about water sources and transport that cannot be obtained from other locally observed variables. Water isotope observations thus provide additional means to evaluate and eventually improve the representation of the water cycle in climate models that prognostically simulate the isotopic composition of atmospheric moisture, an opportunity that should be further explored in future research.
Publications
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Water isotopic characterisation of the cloud–circulation coupling in the North Atlantic trades – Part 1: A process-oriented evaluation of COSMO iso simulations with EUREC 4 A observations. Atmospheric Chemistry and Physics, 23(23), 14643-14672.
Villiger, Leonie; Dütsch, Marina; Bony, Sandrine; Lothon, Marie; Pfahl, Stephan; Wernli, Heini; Brilouet, Pierre-Etienne; Chazette, Patrick; Coutris, Pierre; Delanoë, Julien; Flamant, Cyrille; Schwarzenboeck, Alfons; Werner, Martin & Aemisegger, Franziska
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Linear regression model for predicting moisture sources based on local temperature, specific humidity and isotope values for the western tropical Atlantic
Botsyun, S.
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Moisture transport over the western tropical Atlantic based on the results of COSMO-iso simulations with passive moisture tracers. Goldschmidt2024 abstracts. Geochemical Society.
Botsyun, Svetlana; Villiger, Leonie; Aemisegger, Franziska; Pfahl, Stephan & Kirchner, Ingo
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Quantifying free tropospheric moisture sources over the western tropical Atlantic with numerical water tracers and isotopes. Atmospheric Science Letters, 25(12).
Botsyun, Svetlana; Aemisegger, Franziska; Villiger, Leonie; Kirchner, Ingo & Pfahl, Stephan
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Unraveling the moisture transport in the North Atlantic trade-wind region using passive tracers and stable water isotopes.
Botsyun, Svetlana; Pfahl, Stephan; Aemisegger, Franziska; Villiger, Leonie & Kirchner, Ingo
