Impact of Cloud-Base Turbulence on CCN Activation: CCN Distribution

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

DOI: https://doi.org/10.1175/jas-d-22-0075.1 · OSTI ID:2421428

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

---

1. a Mesoscale and Microscale Meteorology Laboratory, National Center for Atmospheric Research, Boulder, Colorado; OSTI
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 Following our previous investigation of the turbulence impact on cloud-base single-size CCN activation, this study considers a similar problem assuming CCN size distribution obtained from field measurements. The total CNN concentration is taken as either 200 cm⁻³to represent clean conditions, or as 2000 cm⁻³to represent polluted conditions. CCN is assumed to be sodium chloride. The CCN activation in the rising nonturbulent adiabatic parcel is contrasted with the activation within a rising adiabatic parcel filled with inertial-range homogeneous isotropic turbulence. The turbulent parcel of 64³m³and the turbulent kinetic energy dissipation rate of 10⁻³m⁻²s⁻³are used in most of the simulations. Results for a range of mean parcel ascent rates, between 0.125 and 8 m s⁻¹, are discussed. Overall, the adiabatic turbulent parcel simulations show results consistent with the adiabatic nonturbulent parcel, with higher activated CCN concentrations for stronger parcel ascent rates. The key difference is a blurriness of the separation between dry CCN size bins featuring activated and nonactivated (haze) CCN, especially for weak mean ascent rates. The blurriness comes from CCN getting activated and subsequently deactivated in the fluctuating supersaturation field, instead of all becoming cloud droplets above the cloud base. This leads to significantly larger spectral widths in turbulent parcel simulations compared to the nonturbulent parcel when activation is completed. Modeling results are discussed in the context of the impact of turbulent fluctuations on CCN activation documented in laboratory experiments using the Pi chamber.

• Research Organization: University Corporation for Atmospheric Research (UCAR), Boulder, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0020118
• OSTI ID: 2421428
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Journal Issue: 11 Vol. 79; ISSN 0022-4928
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English