Title: Do Ultrafine Cloud Condensation Nuclei Invigorate Deep Convection?

Abstract

Numerical simulations of the impact of ultrafine cloud condensation nuclei (CCN) on deep convection are analyzed herein to investigate the idea proposed by Fan et al. that addition of ultrafine CCN to an otherwise pristine environment leads to convective invigoration. The piggybacking methodology is applied, allowing rigorous separation of the impact of aerosols from different flow realizations that typically occur when even a small element of the model physics or modeling setup is changed. The setup follows the case of daytime convective development over land based on observations during the Large-Scale Biosphere–Atmosphere (LBA) experiment in Amazonia. Overall, the simulated impacts of ultrafine CCN are similar to the previous study by the authors on the impact of pollution on deep convection. There is no convective invigoration above the freezing level, but there is a small invigoration (increase in vertical velocities) below due to the supersaturation and buoyancy differences in conditions with additional ultrafine CCN compared to unperturbed pristine conditions. As in the previous study, the most significant impact is on the upper-tropospheric convective anvils that feature higher cloud fractions in conditions with ultrafine CCN. The increase comes from purely microphysical considerations as the increased cloud droplet concentrations from ultrafine CCN leadmore » to increased ice crystal concentrations and, consequently, smaller sizes and fall velocities, and longer residence times. Mesoscale organization due to low-level shear has a small effect on the simulated ultrafine CCN impacts. Finally, an alternative explanation of increased lightning above oceanic shipping lines seen in satellite observations and argued to result from convective invigoration is provided.« less

Authors:

Grabowski, Wojciech W. ^[1]; Morrison, Hugh ^[1]

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+ Show Author Affiliations

1. National Center for Atmospheric Research, Boulder, CO (United States)

Publication Date:

Wed Jul 08 00:00:00 EDT 2020

Research Org.:

University Corporation for Atmospheric Research, Boulder, CO (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)

OSTI Identifier:

1657808

Grant/Contract Number:  

SC0016476; SC0020104; SC0020118

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the Atmospheric Sciences

Additional Journal Information:

Journal Volume: 77; Journal Issue: 7; Journal ID: ISSN 0022-4928

Publisher:

American Meteorological Society

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; Cloud microphysics; Cumulus clouds; Cloud resolving models