Weakness of the Air-Sea Thermal Coupling during Indian Ocean Dipole Mode in the 1990s

Synopsis We analyze the temporal and spatial variation of the thermal structure of the eastern tropical Indian Ocean associated with Indian Ocean Dipole Mode (IOD), mainly using the water temperature of 10 years (1990-1999) of the World Ocean Circulation Experiment (WOCE) repeat IX1 expendable bathythermograph (XBT) section between Java and Western Australia together with the product of the air-sea coupled four-dimensional variational analysis (4D-VAR) system. The temperature anomaly of the XBT section reveals that the subsurface ocean temperature changes earlier than the surface before the surface IOD pattern starts to grow up. From May to August, a marked subsurface temperature anomaly is also found as well as the sea surface temperature (SST) that is formed primarily by the anomalous coastal upwelling along the south Java coast. Heat budget analysis along IX1 shows that the surface heat flux does not work to enhance the mixed layer temperature anomaly in the eastern pole region.