Geosci. Model Dev. Discuss., 6, 4933-4982, 2013
© Author(s) 2013. This work is distributed
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This discussion paper is under review for the journal Geoscientific Model Development (GMD).
Application and evaluation of McICA scheme with new radiation code in BCC_AGCM2.0.1
H. Zhang1,2, X. Jing1, and J. Li3
1Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing, China
2Nanjing University of Information Science and Technology, Nanjing, China
3Canadian Center for Climate Modeling and Analysis, University of Victoria, Victoria, British Columbia, Canada

Abstract. This research incorporates the Monte Carlo Independent Column Approximation (McICA) scheme with the correlated k-distribution BCC-RAD radiation model into the climate model BCC_AGCM2.0.1 and examines the impacts on modeled climate through several simulations with variations in cloud structures. Results from experiments with consistent sub-grid cloud structures show that both clear-sky radiation fluxes and cloud radiative forcings (CRFs) calculated by the new scheme are mostly improved relative to those calculated from the original one. The modeled atmospheric temperature and specific humidity are also improved due to changes in the radiative heating rates. The vertical overlap of fractional clouds and horizontal distribution of cloud condensation are important for computing CRFs. The maximum changes in seasonal CRF using the general overlap assumption (GenO) with different decorrelation depths (Lcf) are larger than 10 and 20 Wm2 for longwave (LW) CRF and shortwave (SW) CRF, respectively, mostly located in the Tropics and mid-latitude storm tracks. Larger (smaller) Lcf in the Tropics (mid-latitude storm tracks) yield better cloud fraction and CRF compared with observations. The inclusion of an observation-based horizontal inhomogeneity of cloud condensation has a distinct impact on LW CRF and SW CRF, with global means of ∼1.2 Wm−2 and ∼3.7 Wm−2 at the top of atmosphere, respectively, making these much closer to observations. These results prove the reliability of the new model configuration to be used in BCC_AGCM2.0.1 for climate simulations, and also indicate that more detailed real-world information on cloud structures should be obtained to constrain cloud settings in McICA in the future.

Citation: Zhang, H., Jing, X., and Li, J.: Application and evaluation of McICA scheme with new radiation code in BCC_AGCM2.0.1, Geosci. Model Dev. Discuss., 6, 4933-4982, doi:10.5194/gmdd-6-4933-2013, 2013.
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