Oceanic Climatology in the Coupled Model FGOALS-g2:Improvements and Biases

摘要

The present study examines simulated oceanic climatology in the Flexible Global Ocean-Atmosphere-Land System model,Grid-point Version 2 (FGOALS-g2) forced by historical external forcing data.The oceanic temperatures and circulations in FGOALS-g2 were found to be comparable to those observed,and substantially improved compared to those simulated by the previous version,FGOALS-g1.0.Compared with simulations by FGOALS-g1.0,the shallow mixed layer depths were better captured in the eastern Atlantic and Pacific Ocean in FGOALS-g2.In the high latitudes of the Northern Hemisphere,the cold biases of SST were about 1℃ 5℃ smaller in FGOALS-g2.The associated sea ice distributions and their seasonal cycles were more realistic in FGOALS-g2.The pattern of Atlantic Meridional Overturning Circulation (AMOC) was better simulated in FGOALS-g2,although its magnitude was larger than that found in observed data.The simulated Antarctic Circumpolar Current (ACC) transport was about 140 Sv through the Drake Passage,which is close to that observed.Moreover,Antarctic Intermediate Water (AAIW) was better captured in FGOALS-g2.However,large SST cold biases (＞3℃) were still found to exist around major western boundary currents and in the Barents Sea,which can be explained by excessively strong oceanic cold advection and unresolved processes owing to the coarse resolution.In the Indo-Pacific warm pool,the cold biases were partly related to the excessive loss of heat from the ocean.Along the eastern coast in the Atlantic and Pacific Oceans,the warm biases were due to overestimation of shortwave radiation.In the Indian Ocean and Southern Ocean,the surface fresh biases were mainly due to the biases of precipitation.In the tropical Pacific Ocean,the surface fresh biases (＞2 psu) were mainly caused by excessive precipitation and oceanic advection.In theIndo-Pacific Ocean,fresh biases were also found to dominate in the upper 1000 m,except in the northeastern Indian Ocean.There were warm and salty biases (3℃-4℃ and 1-2 psu) from the surface to the bottom in the Labrador Sea,which might be due to large amounts of heat transport and excessive evaporation,respectively.For vertical structures,the maximal biases of temperature and salinity were found to be located at depths of ＞600 m in the Arctic Ocean,and their values exceeded 4℃ and 2 psu,respectively.