Submitted as: development and technical paper 25 Feb 2020
Submitted as: development and technical paper | 25 Feb 2020
Mitigation of the double ITCZ syndrome in BCC-CSM2-MR through improving parameterizations of boundary-layer turbulence and shallow convection
- 1Beijing Climate Center, China Meteorological Administration, Beijing, 100081, China
- 2School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing, 210044, China
- 3School of Atmospheric Sciences, Nanjing University, Nanjing, 210023, China
- 4CMA-NJU Joint Laboratory for Climate Prediction Studies, Nanjing University, Nanjing, 210023, China
- 1Beijing Climate Center, China Meteorological Administration, Beijing, 100081, China
- 2School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing, 210044, China
- 3School of Atmospheric Sciences, Nanjing University, Nanjing, 210023, China
- 4CMA-NJU Joint Laboratory for Climate Prediction Studies, Nanjing University, Nanjing, 210023, China
Abstract. The spurious double intertropical convergence zone (ITCZ) is one of the most prominent systematic biases in coupled atmosphere-ocean general circulation models (CGCMs), and the underestimated marine stratus over eastern subtropical oceans has been recognized as a possible contributor. Rather than modifying the cloud scheme itself, this study significantly promotes the marine stratus simulation through improving parameterizations of boundary-layer turbulence and shallow convection in the medium-resolution Beijing Climate Center Climate System Model version 2 (BCC-CSM2-MR). The University of Washington moist turbulence scheme is implemented in BCC-CSM2-MR to better represent the stratocumulus, and a decoupling criterion is also introduced to the shallow convection scheme for improving the simulation of the stratocumulus-to-cumulus transition. Results show that the simulated precipitation in the eastern Pacific south of the equator is largely reduced, alleviating the double ITCZ problem. The tropical precipitation asymmetry index increases from −0.024 in the original BCC-CSM2-MR to 0.147 in the revised BCC-CSM2-MR, which is much closer to the observation. The study suggests that improving parameterizations of boundary-layer turbulence and shallow convection is effective for mitigating the double ITCZ syndrome in CGCMs.
Yixiong Lu et al.


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RC1: 'Review in File', Anonymous Referee #1, 19 Mar 2020
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AC2: 'Response to Reviewer 1', Yixiong Lu, 07 Aug 2020
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AC2: 'Response to Reviewer 1', Yixiong Lu, 07 Aug 2020
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SC1: 'Executive editor comment: code and data availability.', David Ham, 10 Jul 2020
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AC1: 'Reply to SC1', Yixiong Lu, 11 Jul 2020
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AC1: 'Reply to SC1', Yixiong Lu, 11 Jul 2020
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RC2: 'review of gmd-2020-40', Anonymous Referee #2, 14 Aug 2020
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AC4: 'Response to Reviewer 2', Yixiong Lu, 26 Aug 2020
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AC4: 'Response to Reviewer 2', Yixiong Lu, 26 Aug 2020
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SC2: 'horizontal resolution of atmospheric model matters in the double-ITCZ bias in the coupled model', Fengfei Song, 22 Aug 2020
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AC3: 'Reply to SC2', Yixiong Lu, 25 Aug 2020
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AC3: 'Reply to SC2', Yixiong Lu, 25 Aug 2020
Yixiong Lu et al.
Yixiong Lu et al.
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