Water isotopic characterisation of the cloud-circulation coupling in the North Atlantic trades - Part 2: The imprint of the atmospheric circulation at different scales
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Date
2024-01-23
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Journal Article
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Abstract
Water vapour isotopes reflect the history of moist atmospheric processes encountered by the vapour since evaporating from the ocean, offering potential insights into the controls of shallow trade-wind cumuli. Given that these clouds, particularly their amount at the cloud base level, play an important role in the global radiative budget, improving our understanding of the hydrological cycle associated with them is crucial. This study examines the variability of water vapour isotopes at cloud base in the winter trades near Barbados and explores its connection to the atmospheric circulations ultimately governing cloud fraction. The analyses are based on nested COSMOiso simulations with explicit convection during the EUREC4A (Elucidating the role of clouds-circulation coupling in climate) field campaign. It is shown that the contrasting isotope and humidity characteristics in clear-sky versus cloudy environments at cloud base emerge due to vertical transport on timescales of 4 to 14h associated with local, convective circulations. In addition, the cloud base isotopes are sensitive to variations in the large-scale circulation on timescales of 4 to 6d, which shows on average a Hadley-type subsidence but occasionally much stronger descent related to extratropical dry intrusions. This investigation, based on high-resolution isotope-enabled simulations in combination with trajectory analyses, reveals how dynamical processes at different timescales act in concert to produce the observed humidity variations at the base of trade-wind cumuli.
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published
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Volume
24 (2)
Pages / Article No.
957 - 976
Publisher
Copernicus
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09576 - Bresch, David Niklaus / Bresch, David Niklaus
03854 - Wernli, Johann Heinrich / Wernli, Johann Heinrich
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Funding
188731 - Large-scale circulation drivers and stable water isotope characteristics of low-level clouds over the tropical North Atlantic (SNF)