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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  03 Jul 2020

03 Jul 2020

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This preprint is currently under review for the journal ACP.

Effects of Thermodynamics, Dynamics and Aerosols on Cirrus Clouds Based on In Situ Observations and NCAR CAM6 Model

Ryan Patnaude1, Minghui Diao1, Xiaohong Liu2, and Suqian Chu3 Ryan Patnaude et al.
  • 1Department of Meteorology and Climate Science, San Jose State University, San Jose, 95192, USA
  • 2Department of Atmospheric Sciences, Texas A&M University, College Station, 77843, USA,
  • 3Department of Atmospheric Science, University of Wyoming, Laramie, 82071, USA

Abstract. Cirrus cloud radiative effects are largely affected by ice microphysical properties, including ice water content (IWC), ice crystal number concentration (Ni) and mean diameter (Di). These characteristics vary significantly due to thermodynamic, dynamical and aerosol conditions. In this work, a global-scale observation dataset is used to examine regional variations of cirrus cloud microphysical properties, as well as several key controlling factors, i.e., temperature, relative humidity with respect to ice (RHi), vertical velocity (w), and aerosol number concentrations (Na). Results are compared with simulations from the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 6 (CAM6). The differences between simulations and observations are found to vary with latitude and temperature. Specifically, simulations are found to underestimate IWC by a factor of 5–30 in all regions. Simulated Ni is overestimated in most regions except Northern Hemisphere midlatitude and polar regions. Simulated Di is underestimated, especially for warmer conditions (−50 °C to −40 °C) and higher Na, possibly due to less effective ice particle growth/sedimentation and weaker aerosol indirect effects, respectively. For RHi effects, the frequency and magnitude of ice supersaturation is underestimated in simulations for clear-sky conditions, and the simulated IWC and Ni show maximum values at 80 % RHi instead of 110 % as observed. For w effects, both observations and simulations show variances of w (σw) decreasing from tropics to polar regions, but simulations show much higher σw for in-cloud condition than clear-sky condition. These findings provide an observation-based guideline for improving simulated ice microphysical properties and their relationships with key controlling factors at various geographical locations.

Ryan Patnaude et al.

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Ryan Patnaude et al.

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Latest update: 11 Aug 2020
Publications Copernicus
Short summary
A comprehensive, in-situ observation data set of cirrus clouds was developed based on seven field campaigns, ranging from 87° N–75° S. The observations were compared with a global climate model. Several key factors for cirrus cloud formation were examined, including thermodynamics, dynamics, aerosol indirect effects, and geographical locations. Model biases include lower ice mass concentrations, smaller ice crystals, and weaker aerosol indirect effects.
A comprehensive, in-situ observation data set of cirrus clouds was developed based on seven...