Oceanic impacts on detour of Madden-Julian Oscillation near the Maritime Continent

Madden-Julian Oscillations (MJOs) are the dominant intraseasonal variabilities (ISVs) in the atmosphere acting as a bridge between weather and climate. During boreal winter, about half MJO events originating in the western Indian Ocean propagate eastward reaching the western Pacific and beyond, while about half cannot propagate across the Maritime Continent, but detour southward. Although MJO simulations have been greatly improved in recent years, the mechanism and simulation of MJO detour near the Maritime Continent are still a great scientific challenge. Several mechanisms have been proposed based on atmospheric dynamics and thermodynamics. In this study, the oceanic role in MJO detour is diagnosed using observations and reanalysis products. It is found that warm sea surface temperature (SST) anomalies occur over the southeastern Indian Ocean which induce a cyclone in the lower troposphere. Due to the westerly background winds, westerly (easterly) winds are strengthened (weakened) to the north (south) of warm SST anomalies. As a result, the latent heat flux is enhanced and convection is reinforced to the north of warm SST anomalies. In contrast, the latent heat flux is reduced, and SSTs warm to the south of pre-existing warm SST anomalies. Hence, the warm SST anomalies and convection system associated with MJOs shift southward before they reach the Maritime Continent. The identification of the oceanic influence on the MJO detour deepens our understanding of the mechanism of their detour and elicits the role of the ocean. It is expected to brighten the prospects for better simulation and forecast of MJOs over the Maritime Continent. The oceanic ISVs in the southeastern Indian Ocean are subject to many forcings, such as intraseasonal atmospheric forcing, the Indonesian Throughflow, local oceanic instability, and coastal Kelvin waves along Sumatra. The mechanism of ISVs in the southeastern Indian Ocean requires further dedicated studies.