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Ice and Supercooled Liquid Water Distributions over the Southern Ocean based on In Situ Observations and Climate Model Simulations
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  • Ching An Yang,
  • Minghui Diao,
  • Andrew Gettelman,
  • Kai Zhang,
  • Jian Sun
Ching An Yang
San Jose State University
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Minghui Diao
San Jose State University

Corresponding Author:minghui.diao@sjsu.edu

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Andrew Gettelman
National Center for Atmospheric Research (UCAR)
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Kai Zhang
Pacific Northwest National Laboratory
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Jian Sun
Pacific Northwest National Laboratory (DOE)
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An evaluation of three climate models is conducted using in situ airborne observations from the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) campaign. The evaluation targets cloud phases, microphysical properties, thermodynamic conditions, and aerosol indirect effects at -40°C – 0°C. For cloud phase frequency distribution, the Community Atmosphere Model version 6 (CAM6) shows the most similar result to the observations, which allows more liquid-containing clouds below -10°C compared with its predecessor – CAM5. The Energy Exascale Earth System Model (E3SM) underestimates (overestimates) ice phase frequencies below (above) -20°C. Compared with 580-second averaged observations (i.e., 100 km horizontal scale), CAM6 and E3SM overestimate (underestimate) liquid (ice) water content (i.e., LWC and IWC), leading to lower a glaciation ratio when ice and liquid coexist. Thermodynamic conditions, specifically relative humidity (RH), is likely a key factor contributing to model cloud occurrence and cloud phase biases. Simulated in-cloud RH shows higher minimum values than observations, possibly restricting ice growth during sedimentation. As number concentrations of larger and smaller aerosols (> 500 nm and > 100 nm) increase, observations show increases in glaciation ratio, cloud fraction, LWC and liquid number concentration (Nliq) at -18°C to 0°C, and IWC and ice number concentration (Nice) at -35°C to 0°C. CAM6 and E3SM show slight increases of LWC and Nliq, and E3SM shows small increases of Nice. These results indicate that models underestimate aerosol indirect effects on ice and mixed phase clouds over the Southern Ocean.
27 Dec 2021Published in Journal of Geophysical Research: Atmospheres volume 126 issue 24. 10.1029/2021JD036045