An ensemble subseasonal-to-seasonal forecast system of IAP-CAS model

The coupled model we employed in the IAP-CAS S2S ensemble forecast system is the climate system model CAS FGOALS-f2 (The Flexible Global Ocean-Atmosphere-Land System model Finite Volume version 2, Chinese Academy of Sciences) developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) at the Institute of Atmospheric Physics (IAP), which is part of CAS (Chinese Academy of Sciences). We utilize the institution name, IAP-CAS, as a proxy for the model.

FGOALS-f2 is a fully coupled model that encompasses four components: atmospheric, land, oceanic, and sea ice models, with its configuration detailed in Table 1. The atmospheric component is version 2 of the Finite-volume Atmospheric Model (FAMIL2), with a standard horizontal resolution of C96, which means 96 × 96 grid points in each tile of the cube sphere, roughly equivalent to 1-degree resolution. Vertically, it features 32 hybrid sigma-pressure levels, with the uppermost level situated at 1 hPa (The Hybrid coefficients are listed in Table 2). The land surface component used in FGOALS-f2 is version 4 of the Community Land Model (CLM4.0), featuring a horizontal resolution nearly at 1-degree resolution. The oceanic component is Parallel Ocean Program version 2 (POP2), which utilizes a displaced-pole grid with the North Pole shifted to Greenland. This grid has a resolution of gx1v6, approximately equivalent to a 1-degree horizontal resolution, and includes 60 vertical layers. The sea ice component is the Los Alamos Sea Ice Model version 4.0 (CICE4), sharing the exact horizontal resolution as the ocean model. These four components are coupled via the coupler version 7 in the Community Earth System Model (CESM).