CAS FGOALS-f3-L is a fully coupled climate system model that consists of four component models and one coupled module. The atmospheric model is version 2.2 of the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL) (Zhou et al., 2015; Li et al., 2019), which is the latest generation atmospheric general circulation model developed at LASG/IAP, and employs an efficient dynamical core of finite volume (FV3) (Lin, 2004; Putman and Lin, 2007). The oceanic model is the LASG/IAP Climate System Ocean Model, version 3.0 (LICOM3) (Liu et al., 2012; Li et al., 2017), which is the latest generation oceanic general circulation model developed at LASG/IAP and employs the orthogonal curvilinear coordinate. The land model is the Community Land Model, version 4 (CLM4) (Lawrence et al., 2011), and the sea-ice model is the Community Ice Code, version 4 (CICE4) (Hunke and Lipscomb, 2010). All the component models are coupled via the NCAR Coupler 7 (Craig et al., 2011). Compared with the last version FGOALS-s2 (Bao et al., 2013) in CMIP5, the main changes in CAS FGOALS-f3-L are the atmospheric model and oceanic model. The atmospheric model is updated from the Spectral Atmospheric Model of IAP/LASG, version 2 (SAMIL2) (Bao et al., 2010) to FAMIL, and the oceanic model is updated from LICOM2 (Liu et al., 2012) to LICOM3. Besides CAS FGOALS-f3-L, there is another climate system model from LASG/IAP in CMIP6, which is CAS FGOALS-g3. The main difference between the two models is the atmospheric model employed; the atmospheric model of CAS FGOALS-g3 is the Grid-point Atmospheric Model of IAP/LASG (GAMIL) (Li et al., 2013).
The atmospheric model of CAS FGOALS-f3-L, FAMIL, is established on a finite volume dynamical core on a cubed-sphere grid, with six tiles across the globe and 96 grid cells (C96) for each tile. Globally, there are 384 grid cells in longitude and 192 grid cells in latitude, making the horizontal resolution approximately equal to 1°. In the vertical direction, there are 32 layers using hybrid coordinates, and the top layer of the model is at 2.16 hPa. Several advanced physical schemes have also been employed in the model, which are specifically documented in He et al. (2019). The outputs of FAMIL uploaded to the ESG are postprocessed and interpolated into a longitude–latitude grid of 288 zonal grid cells and 180 meridional gird cells.
For the oceanic model, LICOM3, since the orthogonal curvilinear coordinate is introduced into this version, a tripolar grid with the North Pole split into two poles on two continents at (35°N, 114°E) and (35°N, 66°W), respectively, can be used, which eliminates the singularity of the primitive equations at the North Pole in the normal longitude–latitude dynamic framework and thus improves the related circulations in the Arctic Ocean (Li et al., 2017). The preserved shape advection and the implicit vertical viscosity are also employed in this version. For physical packages, a tidal mixing (Laurent et al., 2002) and a buoyancy frequency (N2) related thickness diffusivity (Ferreira et al., 2005) are introduced into the model, as well as a new vertical diffusivity (Canuto et al., 2001, 2002) and isopycnal mixing (Gent and Mcwilliams, 1990). The low-resolution LICOM3 used here has 360 grid cells in the zonal direction and 218 grid cells in the meridional direction, which is also a globally horizontal resolution approximately equal to 1°, with uneven enhanced meridional resolution from 0.5° to 1° near the equator. In the vertical direction, the resolution is 30 layers, which is 10 m per layer in the upper 150 m and divided in uneven vertical layers below 150 m.
The land model, CLM4, has a longitude–latitude grid of 288 grid cells in longitude and 192 grid cells in latitude, which is approximately equal to 1° globally. The grid of the sea-ice model, CICE4, is the same as LICOM3, which is also a 360 × 218 tripolar grid. Several codes of CICE4 have been adjusted to adapt the tripolar grid of LICOM3. The sea ice in CICE4 is divided into five categories according to ice thickness in each grid cell to better simulate the freezing and melting processes.
Before the historical experiments, the pre-industrial control experiment (piControl) is conducted using the external forcing fixed at the level before industrialization. The piControl experiment is conducted for a long period such that the deep ocean approaches a steady state. Then, the historical experiments are conducted from the variant stable fields generated in the piControl, using the same historical forcing data provided by CMIP6. In this study, as recommended by CMIP6, three ensemble historical experiments are conducted to more clearly identify forced signals emerging from natural variability (Eyring et al., 2016). The three ensembles, labeled as r1i1p1f1, r2i1p1f1 and r3i1p1f1, start from the restart fields generated in the piControl experiment on 1 January of the 600th, 650th and 700th model year, respectively, as the piControl experiment approaches steady state in the deep ocean after about 500 years. All the experiments are shown in Table 1. The historical forcing data provided by CMIP6 represent the observation-based estimates of solar radiation, GHG concentration, land-use change, etc., which are effective to the external forcing of the climate system (Matthes et al., 2017; Meinshausen et al., 2017). The forcing data cover the period from 1850 to 2014, in which the historical experiments are conducted. The outputs of the three ensembles from 1850 to 2014 are postprocessed according to the standards of ESG and then submitted to CMIP6.
Experiment_id Label Initial fields Period Forcing historical r1i1p1f1 1 Jan, 600th year in piControl 1850–2014 CMIP6 historical forcing data historical r2i1p1f1 1 Jan, 650th year in piControl 1850–2014 CMIP6 historical forcing data historical r3i1p1f1 1 Jan, 700th year in piControl 1850–2014 CMIP6 historical forcing data
Table 1. Experiment designs.
|historical||r1i1p1f1||1 Jan, 600th year in piControl||1850–2014||CMIP6 historical forcing data|
|historical||r2i1p1f1||1 Jan, 650th year in piControl||1850–2014||CMIP6 historical forcing data|
|historical||r3i1p1f1||1 Jan, 700th year in piControl||1850–2014||CMIP6 historical forcing data|