Identification

Title

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

Abstract

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.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d73f4ts9

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

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keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

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West bounding longitude

East bounding longitude

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Temporal extent

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End position

Dataset reference date

date type

publication

effective date

2023-10-11T00:00:00Z

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Conformity

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version of format

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Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

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