Abstract
Abstract. BCC-CSM2-HR is a high-resolution version of the Beijing Climate Center (BCC) Climate System Model (T266 in the atmosphere and 1/4∘ latitude × 1/4∘ longitude in the ocean). Its development is on the basis of the medium-resolution version BCC-CSM2-MR (T106 in the atmosphere and 1∘ latitude × 1∘ longitude in the ocean) which is the baseline for BCC participation in the Coupled Model Intercomparison Project Phase 6 (CMIP6). This study documents the high-resolution model, highlights major improvements in the representation of atmospheric dynamical core and physical processes. BCC-CSM2-HR is evaluated for historical climate simulations from 1950 to 2014, performed under CMIP6-prescribed historical forcing, in comparison with its previous medium-resolution version BCC-CSM2-MR. Observed global warming trends of surface air temperature from 1950 to 2014 are well captured by both BCC-CSM2-MR and BCC-CSM2-HR. Present-day basic atmospheric mean states during the period from 1995 to 2014 are then evaluated at global scale, followed by an assessment on climate variabilities in the tropics including the tropical cyclones (TCs), the El Niño–Southern Oscillation (ENSO), the Madden–Julian Oscillation (MJO), and the quasi-biennial oscillation (QBO) in the stratosphere. It is shown that BCC-CSM2-HR represents the global energy balance well and can realistically reproduce the main patterns of atmospheric temperature and wind, precipitation, land surface air temperature, and sea surface temperature (SST). It also improves the spatial patterns of sea ice and associated seasonal variations in both hemispheres. The bias of the double intertropical convergence zone (ITCZ), obvious in BCC-CSM2-MR, almost disappears in BCC-CSM2-HR. TC activity in the tropics is increased with resolution enhanced. The cycle of ENSO, the eastward propagative feature and convection intensity of MJO, and the downward propagation of QBO in BCC-CSM2-HR are all in a better agreement with observations than their counterparts in BCC-CSM2-MR. Some imperfections are, however, noted in BCC-CSM2-HR, such as the excessive cloudiness in the eastern basin of the tropical Pacific with cold SST biases and the insufficient number of tropical cyclones in the North Atlantic.
Highlights
Modelling climate and weather is a major challenge for the scientific community and needs high spatial resolution
This paper was devoted to the presentation of the highresolution version Beijing Climate Center (BCC)-CSM2-HR and to the description of its climate simulation performance
We focused on its updates and differential characteristics from its predecessor, the medium-resolution version BCC-CSM2-MR
Summary
Modelling climate and weather is a major challenge for the scientific community and needs high spatial resolution. Many climate models, such as those involved in the Coupled Model Intercomparison Project Phase 5 (CMIP5, Taylor et al, 2012) and the more recent CMIP6 (Eyring et al, 2016), still use a spatial resolution of hundreds of kilometres (Flato et al, 2013). This nominal resolution is suitable for global-scale applications that run simulations for centuries into the future but fails to capture small-scale phenomena and features that influence local or regional weather and climate events. Many studies (e.g. Ohfuchi et al, 2004; Zhao et al, 2009; Walsh et al, 2012; Bell et al, 2013; Strachan et al, 2013; Kinter et al, 2013; Demory et al, 2014; Schiemann et al, 2014; Small et al, 2014; Shaevitz et al, 2014; Hertwig et al, 2015; Murakami et al, 2015; Roberts et al, 2016; Hewitt et al, 2016; Roberts et al, 2018, 2019) show that enhanced horizontal resolution in atmospheric and ocean models has many beneficial impacts on model performance and helps to reduce model systematic biases
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