SEMINAR: Multi-decadal trends of ocean circulation in the southeast Indian Ocean

On interannual and decadal time scales, the strength of the Leeuwin Current in the southeast Indian Ocean is strongly modulated by climate variability in the tropical Pacific. Stronger trade winds in the Pacific drive a stronger Indonesian throughflow and a stronger Leeuwin Current, due to dynamic connections of the Pacific and the southeast Indian Ocean through equatorial and coastal waveguides. Historical sea level records and reanalysis wind products reveal that the strengthening of the Pacific trade winds since the early-1990’s has reversed their multi-decadal weakening tendency from the 1960’s. These multi-decadal trends of tropical Pacific climate have induced a weakening trend of the Leeuwin Current before 1993, followed by a strengthening trend to the present. Despite the discrepancies of the mean trade winds among atmospheric reanalysis products, all products corroborate the trend reversal of the trade winds during the two multi-decadal periods. The magnitudes of the trade wind reversals along the equatorial Pacific, however, differ among the reanalysis products, which may drive different responses of the Leeuwin Current in numerical models forced by different reanalysis wind products. The observed multi-decadal trends of the internal climate system are larger than the climate-change-induced secular trend during the past few decades, so that long instrumental records are necessary for the detection of human induced global change signals in the ocean circulation system.