Enhancements in cloud condensation nuclei concentrations from turbulent fluctuations in supersaturation

TL;DR

This study demonstrates that small-scale turbulent fluctuations significantly enhance cloud condensation nuclei activation, indicating that current large-scale models likely underestimate cloud droplet formation due to unresolved microphysical interactions.

Contribution

The paper introduces a novel approach using Lagrangian parcel simulations driven by high-resolution LES to quantify turbulence effects on CCN activation, highlighting the importance of unresolved microphysics.

Findings

Small-scale fluctuations increase CCN activation rates.

Neglecting turbulence microphysics leads to underestimation of cloud droplet formation.

Enhanced CCN activation impacts cloud properties and climate predictions.

Abstract

The effect of aerosol emissions on the properties and distribution of clouds is a large source of uncertainty in predictions of weather and climate. These aerosol-cloud interactions depend critically on the ability of aerosol particles to activate into cloud condensation nuclei (CCN). A key challenge in modeling CCN activation and the formation of cloud droplets is the representation of interactions between turbulence and cloud microphysics. Turbulent mixing leads to small-scale fluctuations of water vapor and temperature that are not resolved in large-scale atmospheric models. We used Lagrangian parcel simulations driven by a high-resolution Large Eddy Simulation of a convective cloud chamber to quantify the impact of these small-scale fluctuations on CCN activation. We show that small-scale fluctuations in environmental properties strongly enhance CCN activation, which suggests that conventional Large Eddy Simulations and Earth System Models that neglect these fluctuations underestimate cloud droplet formation.