Linking the Subsurface Indian Ocean Dipole to Central Pacific ENSO

We identified a remote linkage from the Central Pacific (CP) El Nino-Southern Oscillation (ENSO) to the subsurface Indian Ocean dipole (Sub-IOD) occurring in winter-to-spring. Although most Sub-IOD events co-occur with a surface Indian Ocean dipole (IOD) in autumn, some Sub-IOD events develop independently in winter-to-spring. These spring Sub-IODs are usually accompanied by a CP ENSO event that develops in the winter, peaks in early spring, and has a more westward-located sea surface temperature anomaly over the central equatorial Pacific (around 180 degrees E). The sea surface temperature anomaly and the accompanying surface zonal wind anomalie during these western CP El Nino (La Nina) events contributes to an anomalous descending (ascending) branch of the Walker circulation over the Indo-Pacific region and easterly (westerly) anomalies over the equatorial Indian Ocean from winter to the following spring. This helps to trigger a positive (negative) Sub-IOD event. Plain Language Summary As a crucial ocean dynamic factor that may promote the development of the surface Indian Ocean dipole (IOD), most subsurface IOD (Sub-IOD) events co-occur with the IOD in autumn when the ocean thermocline and the atmospheric circulation over the equatorial Indian Ocean are favorable. However, we found that some Sub-IOD events may occur in winter-to-spring without an IOD-related triggering mechanism. We identified a remote linkage from the Central Pacific (CP) El Nino-Southern Oscillation (ENSO) to the occurrence of Sub-IODs in winter-to-spring. A CP El Nino (La Nina) event in winter tends to be followed by a positive (negative) Sub-IOD event in the following spring. These western-type CP ENSO events that peak in spring show sea surface temperature anomalies that have their center further to the west (up to 180 degrees E) and can yield significant zonal wind anomalies over the equatorial Indian Ocean through the atmospheric bridge, triggering Sub-IODs in spring when the IOD is absent.