Examination of interannual variability of sea surface temperature in the Indian Ocean using the physical decomposition method

The physical decomposition method suggested by Qian (2012) is used to examine the interannual variability of sea surface temperature (SST) and anomaly (SSTA) in the Indian Ocean (IO) for the period 1945−2003. The monthly mean SSTs taken from the global ocean reanalysis produced by the Simple Ocean Data Assimilation (SODA) are decomposed into four terms. The first term is the zonally averaged monthly climatological SST ([ ( )]) Tt ϕ , which features relatively warm surface waters in the tropical IO and relatively colder surface waters over the southern IO. This term also has a relatively low SST pool between the Equator and 20°N. The SST at the center of the pool in summer is about 1−2°C lower than in spring and autumn. The second term is the spatially-varying monthly climatological SSTA * ( ( , )) Tt λ ϕ , due mainly to the topographic effect and seasonal variation in wind forcing. The values of * (,) Tt λ ϕ are negative over the western coastal waters and positive over the eastern coastal and shelf waters in the tropical and northern IO. The third term is the zonally-averaged transient SSTA ([ ( , ) ] ) T t ϕ Y ′ . The largest values of [ ( , )] T t ϕ Y ′ occur over the subtropical and mid-latitudes of the IO, which differs from the SSTA in the tropical waters of the Pacific Ocean. Time series of zonally and meridionally averaged ( ,) T t ϕ Y ′ in the tropical-subtropical IO is strongly correlated with the Indian Ocean basin-wide (IOBW) mode. The fourth term is the spatially-varying transient SSTA * ( ( , ,) ) T t λ ϕ Y′ . The REOF analysis of the fourth term demonstrates that the first REOF is correlated strongly with the South Indian Ocean Dipole (SIOD) mode. The second REOF is correlated strongly with the equatorial Indian Ocean dipole (IOD) mode. The third REOF is highly correlated with the tropical IOBW mode.