Impact of Cloud-Base Turbulence on CCN Activation: Single-Size CCN

Journal Article · 31 January 2022 · Journal of the Atmospheric Sciences

DOI: https://doi.org/10.1175/JAS-D-21-0184.1 · OSTI ID:1844279

Grabowski, Wojciech W. ^[1]; Thomas, Lois ^[2]; Kumar, Bipin ^[3]

---

1. a Mesoscale and Microscale Meteorology Laboratory, National Center for Atmospheric Research, Boulder, Colorado
2. b HPCS, Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune, India, c Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune, India
3. b HPCS, Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune, India

Abstract This paper examines the impact of cloud-base turbulence on activation of cloud condensation nuclei (CCN). Following our previous studies, we contrast activation within a nonturbulent adiabatic parcel and an adiabatic parcel filled with turbulence. The latter is simulated by applying a forced implicit large-eddy simulation within a triply periodic computational domain of 64 ³ m ³ . We consider two monodisperse CCN. Small CCN have a dry radius of 0.01 μ m and a corresponding activation (critical) radius and critical supersaturation of 0.6 μ m and 1.3%, respectively. Large CCN have a dry radius of 0.2 μ m and feature activation radius of 5.4 μ m and critical supersaturation 0.15%. CCN are assumed in 200-cm ⁻³ concentration in all cases. Mean cloud-base updraft velocities of 0.33, 1, and 3 m s ⁻¹ are considered. In the nonturbulent parcel, all CCN are activated and lead to a monodisperse droplet size distribution above the cloud base, with practically the same droplet size in all simulations. In contrast, turbulence can lead to activation of only a fraction of all CCN with a nonzero spectral width above the cloud base, of the order of 1 μ m, especially in the case of small CCN and weak mean cloud-base ascent. We compare our results to studies of the turbulent single-size CCN activation in the Pi chamber. Sensitivity simulations that apply a smaller turbulence intensity, smaller computational domain, and modified initial conditions document the impact of specific modeling assumptions. The simulations call for a more realistic high-resolution modeling of turbulent cloud-base activation.

• Sponsoring Organization: USDOE
• Grant/Contract Number: NONE; SC0020118
• OSTI ID: 1844279
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Journal Issue: 2 Vol. 79; ISSN 0022-4928
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English