Indian Ocean Warming During 1950–2005 Determined by Flexible Global Ocean–Atmosphere–Land System Model (FGOALS)

Abstract

The Indian Ocean has exhibited a basin-wide warming trend during the twentieth century, particularly since the 1950s. This trend is effectively reproduced by version 2 of the grid-point and spectral versions of the Flexible Global Ocean–Atmosphere–Land System (FGOALS) model, FGOALS-g2 and FGOALS-s2, respectively. The pattern correlation coefficient and root-mean-square-difference (RMSE) in warming patterns between HadISST and FGOALS-g2 (FGOALS-s2) are 0.92 (0.90) and 0.31 K (0.38 K), respectively. The trend of the Indian Ocean averaged sea surface temperature (SST) from HadISST is 0.63 K (56-year)⁻¹, which is underestimated in FGOALS-g2 at 0.47 K (56-year)⁻¹ and overestimated in FGOALS-s2 at 0.78 K (56-year)⁻¹. In addition, FGOALS-g2 (FGOALS-s2) underestimates (overestimates) the amplitude of interannual variability during 1950–2005. The warming mechanisms in each model are investigated by the diagnosis of the Indian Ocean mixed layer heat budget, which demonstrates that the basin-wide warming trends in the Indian Ocean in both FGOALS models are primarily caused by atmospheric forcing via radiative and turbulent fluxes. Among them, the surface latent heat flux from atmosphere and surface longwave radiation trends are most important parameters in forming the basin-wide warming trend. However, decreased surface shortwave radiation cools most of the Indian Ocean basin.