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Title: Effects of pre-existing ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5)

In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmosphere Model version 5.3 (CAM5.3), the effects of pre-existing ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of the cirrus cloud rather than in the whole area of the cirrus cloud. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The pre-existing ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and pre-existing ice effects simulated by the three ice nucleationmore » parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m-2) is less than that from the LP (8.46 × 106 m-2) and BN (5.62 × 106 m-2) parameterizations. As a result, the experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long-wave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m−2) and BN (0.39 W m-2) parameterizations.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Univ. of Wyoming, Laramie, WY (United States); Hebei Key Lab. for Meteorology and Eco-environment, Shijiazhuang (China); Hebei Climate Center, Shijiazhuang (China)
  2. Univ. of Wyoming, Laramie, WY (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1184955
Report Number(s):
PNNL-SA-103838
Journal ID: ISSN 1680-7324; KP1703020
Grant/Contract Number:
AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 15; Journal Issue: 3; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; ice crystals; cirrus clouds; ice nucleation parameterizations; Community Atmosphere Model; CAM5