Intraseasonal responses of sea surface and deep oceanic temperature anomalies in the northern Indian Ocean–western Pacific to the 30–60-day boreal summer atmospheric intraseasonal oscillation

Jiangyu MAO and Ming Wang, Institute of Atmospheric Physics, Beijing, China
The 30–60-day boreal summer atmospheric intraseasonal oscillation (BSISO) is the predominant intraseasonal variability of the Asian summer monsoon, and has a strong dynamical and thermodynamical impact on the underlying oceans in the northern Indian Ocean–western Pacific. This study uses composite analysis of satellite-observed sea surface temperature (SST) data, as well as atmospheric and oceanic reanalysis datasets for the period 1998–2013, to identify the intraseasonal behavior of SST and deep ocean temperatures during the life cycle of the BSISO. With the BSISO as an organized entity evolving both eastward and northward from the equatorial Indian Ocean, the BSISO-induced SST anomalies propagate coherently into several basins, including the Arabian Sea, Bay of Bengal, South China Sea, and western Pacific, characterized by the alternate occurrence of basin-wide positive and negative SST anomalies, which primarily respond to the active and suppressed convection phases of the BSISO due to anomalous southwesterlies and northeasterlies together with the resultant surface heating anomalies. Significant BSISO-induced oceanic temperature anomalies occur in the equatorial Indian Ocean and western Pacific, with the largest-amplitude anomalous signals arising around the thermocline and extending downward into the deep ocean to below 1000 m or more, which are associated with the equatorial eastward-propagating oceanic Kelvin waves forced by anomalous surface wind stress. However, the local and remote effects of such equatorial oceanic Kelvin waves on the SST and deep oceanic temperature anomalies, especially north of the equator, differ from different basins through the consequential coastal Kelvin waves and reflected Rossby waves.