Seasonal Cooling in the Southeastern Indian Ocean and the Madden-Julian Oscillation

Abstract:

Our previous study showed that the annual oceanic Rossby wave contributes to the westward advection of cold water in the southeastern Indian Ocean, resulting in abrupt cooling and lagged convective onset of the Madden-Julian Oscillation in the central south Indian Ocean during the cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011). In this study, the relationship between seasonal cooling associated with the Rossby wave and the Madden-Julian Oscillation in boreal winter (October to March) is examined for the period of 1993-2012. The westward propagation of positive sea level anomalies (as a proxy of the Rossby wave) is found in most of years but its amplitude and date of arrival in central south Indian Ocean vary from year to year. Warm SST anomalies migrate concurrently with the downwelling Rossby wave but are followed by a wide-spread cold pool in the southeastern Indian Ocean. During El Niño and/or positive Indian Ocean Dipole years, the Rossby waves tend to have larger amplitudes and the cold pool spread more widely than the other years. The first MJO events of the year which propagate from the Indian Ocean to the Pacific are found around and after the cold pool termination. Thus, the southeastern Indian Ocean cold pool may prevent intraseasonal convection in the Indian Ocean from propagating eastward to the Pacific.