Oceanic Processes in Ocean Temperature Products Key to a Realistic Presentation of Positive Indian Ocean Dipole Nonlinearity

A positive Indian Ocean Dipole (pIOD) refers to a sea surface temperature anomaly pattern with cold anomalies in the equatorial eastern Indian Ocean and warm anomalies in the west, leading to floods in the eastern African countries and droughts and bushfires in Indonesia and Australia. The pIOD displays strong inter-event differences, ranging from an extreme event dominated by westward-extended strong cold anomalies along the equator, to a moderate event with weakened cooling confined to region off Sumatra-Java. Representation of the extreme pIOD varies vastly across ocean temperature products. Here we show that products generated in a system explicitly involving subsurface oceanic processes capture the nonlinear dynamics of the extreme pIOD, i.e., the equatorial nonlinear zonal and vertical advection, and systematically produce a more realistic extreme pIOD. Thus, our study identifies ocean temperature products that are more suitable for studying extreme pIOD and its climatic impacts. Plain Language Summary A positive Indian Ocean Dipole (pIOD), with warm and cold sea surface temperature anomalies in the western and eastern equatorial Indian Ocean, respectively, exerts a pronounced impact on the climate extremes, including floods in the eastern African countries and droughts and bushfires in Indonesia and Australia. However, pIOD events vary vastly in amplitude and spatial pattern from one event to another, ranging from extreme events dominated by westward-extended strong cold anomalies along the equator, to moderate events with weakened cooling confined to region off Sumatra-Java. Any product must realistically represent the inter-event difference, because impacts of the extreme and moderate events are rather different. Here we find that ocean temperature products that explicitly involve oceanic processes, in particular, the equatorial oceanic nonlinear zonal and vertical advection, in their construction produce marked pIOD inter-event differences, particularly a greater amplitude of extreme pIODs, than in products that do not. Thus, ocean temperature products that involve oceanic processes are more advantageous for use in pIOD research.