ISOLESC: A coupled isotope-LSM-LES-Cloud modeling system to investigate the water budget in the atmospheric boundary layer

This paper presents a description of an atmospheric boundary layer (ABL) simulation system called ISOLESC that couples water isotope fractionation processes with a land surface model, a large eddy simulation model, and a two-moment cloud microphysics parameterization. Results from two model configurations-one with shallow precipitating cumulus and the other for a cloud-free ABL-are presented to evaluate the model performance and determine its sensitivity to isotopic parameterizations.

The coupled model successfully reproduces important ABL statistics (ABL height, cloud fraction, and cloud liquid water content), the expected effects of mixing and fractionation on the time evolution of ABL vapor isotopic composition, and observed diurnal variations of near-surface water vapor isotopic composition. For the current configuration, nondiscriminating entrainment contributes 17% to the subdaily time variation of near-surface vapor deuterium excess, while surface evapotranspiration contributes 83%.