Interannual upper ocean variability in the tropical Indian Ocean

Empirical orthogonal function (EOF) analysis is used to characterize intera nnual upper ocean temperature variability since mid-1980s along two repeate d XBT sections across the Indian Ocean. The mode I EOF loadings have deepen ed thermocline in the western tropical Indian Ocean and a shoal thermocline in the east/southeast Indian Ocean during the 1994 and 1997/98 Indian Ocea n dipole (IOD) events. Reversed anomalies occur during 1988/89, 1996, and 1 998/99. The mode 2 EOF loadings only have significant magnitudes related to the IOD, with upwelling (downwelling) along the Sumatra-Java coast and dow nwelling (upwelling) in the southern subtropics leading (lagging) the IOD p eaks. Lagged correlations between sea level anomaly and westward wind stres s anomaly along the equatorial Indian Ocean (an IOD index) support the EOF analysis: the two EOF modes are linked by propagation and reflection of sub tropical Rossby waves and equatorial Kelvin waves, which also contribute to reverse the IOD through a delayed action.