Long-term Stability and Oceanic Mean State Simulated by the Coupled Model FGOALS-s2

We describe the long-term stability and mean climatology of oceanic circulations simulated by version 2 of the Flexible Global Ocean--Atmosphere--Land System model (FGOALS-s2). Driven by pre-industrial forcing, the integration of FGOALS-s2 was found to have remained stable, with no obvious climate drift over 600 model years. The linear trends of sea SST and sea surface salinity (SSS) were -0.04oC (100 yr)-1 and 0.01 psu (100 yr)-1, respectively. The simulations of oceanic temperatures, wind-driven circulation and thermohaline circulation in FGOALS-s2 were found to be comparable with observations, and have been substantially improved over previous FGOALS-s versions (1.0 and 1.1). However, significant SST biases (exceeding 3oC) were found around strong western boundary currents, in the East China Sea, the Sea of Japan and the Barents Sea. Along the eastern coasts in the Pacific and Atlantic Ocean, a warm bias (>3oC) was mainly due to overestimation of net surface shortwave radiation and weak oceanic upwelling. The difference of SST biases in the North Atlantic and Pacific was partly due to the errors of meridional heat transport. For SSS, biases exceeding 1.5 psu were located in the Arctic Ocean and around the Gulf Stream. In the tropics, freshwater biases dominated and were mainly caused by the excess of precipitation. Regarding the vertical dimension, the maximal biases of temperature and salinity were located north of 65oN at depths of greater than 600 m, and their values exceeded 4oC and 2 psu, respectively.