Search for: All records

Indian Ocean meridional heat transport (MHT_IO) drives climate and ecosystem impacts, through changes to ocean temperature. Improved understanding of natural variability in tropical and subtropical MHT_IOis 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 MHT_IO. However, it is unclear whether internally generated IOD can drive variability in MHT_IO, or if the apparent relationship between IOD and MHT_IOarises 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 MHT_IO. We find that IOD is not linked to anomalies in MHT_IO. Nevertheless, internal atmospheric variability drives significant MHT_IOvariability. There is little evidence for decadal or multidecadal variability in MHT_IO, suggesting this may be a region where an anthropogenic trend rises above the level of internal variability sooner.

Identifying the origins of wintertime climate variations in the Northern Hemisphere requires careful attribution of the role of El Niño–Southern Oscillation (ENSO). For example, Aleutian low variability arises from internal atmospheric dynamics and is remotely forced mainly via ENSO. How ENSO modifies the local sea surface temperature (SST) and North American precipitation responses to Aleutian low variability remains unclear, as teasing out the ENSO signal is difficult. This study utilizes carefully designed coupled model experiments to address this issue. In the absence of ENSO, a deeper Aleutian low drives a positive Pacific decadal oscillation (PDO)-like SST response. However, unlike the observed PDO pattern, a coherent zonal band of turbulent heat flux–driven warm SST anomalies develops throughout the subtropical North Pacific. Furthermore, non-ENSO Aleutian low variability is associated with a large-scale atmospheric circulation pattern confined over the North Pacific and North America and dry precipitation anomalies across the southeastern United States. When ENSO is included in the forcing of Aleutian low variability in the experiments, the ENSO teleconnection modulates the turbulent heat fluxes and damps the subtropical SST anomalies induced by non-ENSO Aleutian low variability. Inclusion of ENSO forcing results in wet precipitation anomalies across the southeastern United States, unlike when the Aleutian low is driven by non-ENSO sources. Hence, we find that the ENSO teleconnection acts to destructively interfere with the subtropical North Pacific SST and southeastern United States precipitation signals associated with non-ENSO Aleutian low variability.