Tropical oceanic intraseasonal variabilities associated with central Indian Ocean mode

The oceanic intraseasonal variabilities (ISVs) are pronounced over the tropical Indian Ocean. Recently, a Central Indian Ocean (CIO) mode was proposed as an ocean–atmosphere coupled mode at intraseasonal timescales. It has a close relation with northward-propagating ISVs and intraseasonal precipitation during the Indian summer monsoon. In this study, the dynamics of tropical oceanic ISVs associated with the CIO mode are analyzed using reanalysis products and observations. A complete heat budget analysis shows that intraseasonal SST anomalies which propagate westward from the eastern to the central tropical Indian Ocean during the CIO mode are mainly attributable to zonal thermal advection. Surface heat flux is the second largest contributor. This is distinct from the traditional tropical oceanic ISVs as a response to the Madden–Julian Oscillation (MJO) in the atmosphere, in which surface heat flux is usually the dominant component. Current results along with the previously reported atmosphere dynamics during the CIO mode depict a framework for the ocean–atmosphere coupled mode over the tropical Indian Ocean. This represents a more comprehensive understanding of tropical ISVs and will ultimately contribute to the improvement in process understanding, simulations, and forecasts of the Indian summer monsoon.