Interannual variability of the Eastern Indian Ocean with focus on the Ningaloo Niño and negative Indian Ocean Dipole event in 2010/2011

The dominant mode of sea surface temperature (SST) variability in the southeast Indian Ocean off the coast of Western Australia is called Ningaloo Niño/Niña. An unprecedented Ningaloo Niño, or marine heatwave, occurred during the austral summer of 2010/2011 with mean SSTs at 3°C above the long-term mean and had drastic impacts on the ecosystem. This event was attributed to a combination of an anomalous strong Leeuwin Current and high local air-sea heat fluxes. A number of local and remote forcing mechanisms have been investigated in recent years, however, little is known about the depth-structure of these ocean extremes and their general connections to large-scale ocean interannual to decadal variability. Using a suite of simulations with a high-resolution global Ocean General Circulation Model from 1958-2016, we investigate eastern Indian Ocean variability with focus on Ningaloo Niño and corresponding cold Ningaloo Niña events. In particular, we are interested in the impacts of large-scale ocean and climate variability, such as the Indonesian Throughflow, El Niño - Southern Oscillation and the Indian Ocean Dipole (IOD), on the study region. Spatial composites reveal large-scale surface and subsurface anomalies that extend from the western Pacific across the Indonesian Archipelago into the tropical eastern Indian Ocean. In particular, strong anomalies in temperature, salinity and mixed layer depth are found to the west of Sumatra and Java, a region that is generally strongly impacted by the IOD. We therefore investigate the connection with Ningaloo Niño/Niña events, at surface and subsurface, with a focus on 2010/2011 where a strong negative IOD event occurred prior to the unprecedented Ningaloo Niño. Furthermore, we find that major heatwaves in 2000 and 2011 are associated with pronounced fresh anomalies. Sensitivity experiments allow us to assess the relative role of buoyancy and wind-forcing as drivers of the observed patterns. Our work can provide valuable contributions for advancing the understanding of Ningaloo Niño/Niña drivers from surface to depth and regional to large scales.