Vertical Structure and Ice Production Processes of Shallow Convective Postfrontal Clouds over the Southern Ocean in MARCUS. Part I: Observational Study

A study of the vertical structure of postfrontal shallow clouds in the marine boundary layer over the Southern Ocean is presented. The central question of this two-part study regards cloud phase (liquid/ice) of precipitation, and the associated growth mechanisms. In this first part, data from the Me...

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Bibliographic Details
Published in:Journal of the atmospheric sciences Vol. 80; no. 5; pp. 1285 - 1306
Main Authors: Hu, Yazhe, Geerts, Bart, Deng, Min, Grasmick, Coltin, Wang, Yonggang, Lackner, Christian Philipp, Hu, Yishi, Lebo, Zachary J., Zhang, Damao
Format: Journal Article
Language:English
Published: United States American Meteorological Society 01.05.2023
Subjects:
Boundary layer
Cloud microphysics
Mesoscale systems
Southern Ocean
ISSN:0022-4928, 1520-0469
Online Access:Get full text
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Summary:A study of the vertical structure of postfrontal shallow clouds in the marine boundary layer over the Southern Ocean is presented. The central question of this two-part study regards cloud phase (liquid/ice) of precipitation, and the associated growth mechanisms. In this first part, data from the Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean (MARCUS) field campaign are analyzed, starting with a 75-h case with continuous sea surface-based thermal instability, modest surface heat fluxes, an open-cellular mesoscale organization, and very few ice nucleating particles (INPs). The clouds are mostly precipitating and shallow (tops mostly around 2 km above sea level), with weak up- and downdrafts, and with cloud-top temperatures generally around −18° to −10°C. The case study is extended to three other periods of postfrontal shallow clouds in MARCUS. While abundant supercooled liquid water is commonly present, an experimental cloud-phase algorithm classifies nearly two-thirds of clouds in the 0° to −5°C layer as containing ice (cloud ice, snow, or mixed phase), implying that much of the precipitation grows through cold-cloud processes. The best predictors of ice presence are cloud-top temperature, cloud depth, and INP concentration. Measures of convective activity and turbulence are found to be poor indicators of ice presence in the studied environment. The water-phase distribution in this cloud regime is explored through numerical simulations in Part II.
Bibliography:SC0018927
None
USDOE Office of Science (SC), Biological and Environmental Research (BER)
ISSN:0022-4928
1520-0469
DOI:10.1175/JAS-D-21-0243.1