Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Water vapour isotopes reflect the history of moist atmospheric processes encountered by the vapour since evaporation from the ocean. This study focuses on water isotope variability in the winter trades near Barbados at cloud base, which has been identified as an important level for understanding the net radiative effects of shallow cumuli. The analyses are based on nested convection resolving COSMO<sub>iso</sub> simulations during the EUREC<sup>4</sup>A field campaign. The two main findings are that (i) the contrasting isotope and humidity characteristics in clear-sky versus cloudy cloud base environments emerge due to vertical transport on time scales of 12 hours associated with local, convective circulations and show a clear diel cycle; and (ii) the cloud base isotopes are, in addition, sensitive to variations in the large-scale circulation on time scales of several days, 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 scales act in concert to produce the observed humidity variations at the base of trade-wind cumuli.
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