Sub-cloud rain evaporation in the North Atlantic winter trade winds derived by pairing isotopic data with a bin-resolved microphysical model

Sub-cloud rain evaporation in the trade wind region significantly influences the boundary layer mass and energy budgets. Parameterizing it is, however, difficult due to the sparsity of well-resolved rain observations and the challenges of sampling short-lived marine cumulus clouds. In this study, sub-cloud rain evaporation is analyzed using a steady-state, one-dimensional model that simulates changes in drop sizes, relative humidity, and rain isotopic composition. The model is initialized with relative humidity, raindrop size distributions, and water vapor isotope ratios (e.g., delta D v , delta 18 O v ) sampled by the NOAA P3 aircraft during the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC), which was part of the larger EUREC 4 A (ElUcidating the RolE of Clouds-Circulation Coupling in ClimAte) field program. The modeled surface precipitation isotope ratios closely match the observations from EUREC 4 A ground-based and ship-based platforms, lending credibility to our model. The model suggests that 63 % of the rain mass evaporates in the sub-cloud layer across 22 P3 cases. The vertical distribution of the evaporated rain flux is top heavy for a narrow ( sigma ) raindrop size distribution (RSD) centered over a small geometric mean diameter ( D g ) at the cloud base. A top-heavy profile has a higher rain-evaporated fraction (REF) and larger changes in the rain deuterium excess ( d = delta D - 8 x delta 18 O ) between the cloud base and the surface than a bottom-heavy profile, which results from a wider RSD with larger D g . The modeled REF and change in d are also more strongly influenced by cloud base D g and sigma rather than the concentration of raindrops. The model results are accurate as long as the variations in the relative humidity conditions are accounted for. Relative humidity alone, however, is a poor indicator of sub-cloud rain evaporation. Overall, our analysis indicates the intricate dependence of sub-cloud rain evaporation on both thermodynamic and microphysical processes in the trade wind region.

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Related Links

Related Dataset #1 : Calibrated stable water isotope data in precipitation from the BCO during EUREC4A

Related Dataset #2 : M161 Rainwater Isotopic Composition

Related Dataset #3 : ATOMIC ship ceilometer: Cloud base height and vertical profiles of visible light backscattered from aerosols and clouds in the atmospheric boundary layer estimated from a vertically-pointing lidar remote sensing instrument aboard NOAA Ship Ronald H. Brown in the North Atlantic Ocean, near Barbados: Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign 2010-01-09 to 2010-02-12 (NCEI Accession 0225425)

Related Dataset #4 : ATOMIC ship disdrometer: Rain rate, rain accumulation, raindrop count, and equivalent radar reflectivity from disdrometer aboard NOAA Ship Ronald H. Brown in the North Atlantic Ocean, near Barbados, at the native time resolution of 10 seconds: Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign 2020-01-09 to 2020-02-12 (NCEI Accession 0225426)

Related Dataset #5 : ATOMIC aircraft microphysics: Size-resolved cloud and aerosol number concentrations taken from N43 aircraft in the North Atlantic Ocean, Barbados: Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign 2020-01-31 to 2020-02-10 (NCEI Accession 0232458)

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Author Sarkar, Mampi
Bailey, Adriana
Blossey, P.
de Szoeke, S. P.
Noone, D.
Quiñones Meléndez, E.
Leandro, M. D.
Chuang, P. Y.
Publisher UCAR/NCAR - Library
Publication Date 2023-10-11T00:00:00
Digital Object Identifier (DOI) Not Assigned
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Topic Category geoscientificInformation
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Metadata Date 2025-07-11T15:13:46.044045
Metadata Record Identifier edu.ucar.opensky::articles:27002
Metadata Language eng; USA
Suggested Citation Sarkar, Mampi, Bailey, Adriana, Blossey, P., de Szoeke, S. P., Noone, D., Quiñones Meléndez, E., Leandro, M. D., Chuang, P. Y.. (2023). Sub-cloud rain evaporation in the North Atlantic winter trade winds derived by pairing isotopic data with a bin-resolved microphysical model. UCAR/NCAR - Library. https://n2t.org/ark:/85065/d73f4ts9. Accessed 02 August 2025.

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