ENSO Explains the Link Between Indian Ocean Dipole and Meridional Ocean Heat Transport

• Published in: Geophysical research letters 2022-01, Vol.49 (2), p.n/a
• Main Authors: McMonigal, K., Larson, Sarah M.
• Format: Article
• Language: English
• Subjects: Anomalies; Anthropogenic factors; Atmospheric models; Atmospheric variability; Climate; Climate change; Climate models; Climate prediction; Climate variability; coupled climate modes; Dipoles; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; ENSO; Environmental impact; Heat; Heat transport; Human influences; Indian ocean; Indian ocean dipole; Indonesian Throughflow; Marine ecosystems; Meridional heat transport; Natural variability; Ocean basins; ocean heat transport; Ocean temperature; Oceans; Southern Oscillation; Tropical climate; Variability
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL095796

Indian Ocean meridional heat transport (MHTIO) drives climate and ecosystem impacts, through changes to ocean temperature. Improved understanding of natural variability in tropical and subtropical MHTIO is needed to contextualize observations and future projections. Previous studies suggest that El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) can drive variability in MHTIO. However, it is unclear whether internally generated IOD can drive variability in MHTIO, or if the apparent relationship between IOD and MHTIO arises because both are modulated by ENSO. Here, we use a model experiment which dynamically removes ENSO to determine the role of internally forced IOD on MHTIO. We find that IOD is not linked to anomalies in MHTIO. Nevertheless, internal atmospheric variability drives significant MHTIO variability. There is little evidence for decadal or multidecadal variability in MHTIO, suggesting this may be a region where an anthropogenic trend rises above the level of internal variability sooner. Plain Language Summary To assess changes occurring in the Indian Ocean and to understand future projected changes, we need to understand the natural variability in the basin. Heat enters the Indian Ocean from the Pacific through the Indonesian Throughflow, and exits the basin at the southern boundary. The transport of heat southward through the Indian Ocean is termed the meridional heat transport (MHTIO). To investigate the natural variability in MHTIO, we compare climate models with and without El Niño Southern Oscillation (ENSO). This allows us to determine which variability is caused by ENSO and which is internal to the basin. We find that internal variability in MHTIO is mostly caused by internal atmospheric variability, which has little predictability. Modes of climate variability with more predictive power, such as the Indian Ocean Dipole and Indian Ocean Basin Mode are not correlated with MHTIO after removing ENSO. Key Points The wind pattern associated with IOD does not drive anomalous Indian Ocean meridional heat transport (MHTIO) Internally forced and ENSO forced IOD drive different wind patterns and MHTIO responses Internally forced MHTIO variability south of 15°S is driven by an Ekman response to anticyclonic wind stress