We examine observational data to clarify impacts of three major climate
modes on Sea Surface Height Anomaly (SSHA) of the Indian Ocean during
1993-2016: The El Niño and Southern Oscillation (ENSO), the Indian Ocean
Dipole mode (IOD) and the Asian summer monsoon. ENSO and IOD dominantly
control the SSHA in the eastern tropical area and in the western
tropical and northwestern areas of the Indian Ocean, respectively, while
the monsoon contributes to local SSHA.
For all climate modes, SSHA is primarily linked to the wind-forced ocean
upwelling. In particular, the trade-wind and alongshore-wind changes
associated with ENSO- and IOD-related atmospheric convection clearly
control the equatorial and coastal upwelling of the tropical areas. The
net heat flux anomaly at the sea surface always works to damp the
tropical SSHAs. In the northwestern areas, on the other hand, it can
contribute to enhancing the SSHAs relevant to IOD and monsoon.