17 January 2018

Contributions of Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation to Global Ocean Heat Content Distribution


Regional sea surface temperature (SST) mode variabilities, especially the La Niña-like Pacific Ocean temperature pattern known as the negative phase of the Interdecadal Pacific Oscillation (IPO), and the associated heat redistribution within the ocean are the leading mechanisms explaining the recent global warming hiatus. Here we use the Community Earth System Model (CESM) version 1, to examine how different phases of two leading decadal timescale SST modes, namely the IPO and the Atlantic Multidecadal Oscillation (AMO), contribute to heat redistribution in the global ocean in the absence of time evolving external forcings.


Our results show that both the IPO and AMO contribute a similar magnitude to global mean surface temperature and ocean heat redistribution.  Both modes contribute warmer surface temperature and higher upper ocean heat content in their positive phase, and the reverse in their negative phase. Regionally, patterns of ocean heat distribution in the upper few hundred meters of the tropical and subtropical Pacific Ocean depend highly on the IPO phase via the IPO associated changes in the subtropical cell. In the Atlantic, ocean heat content is primarily associated with the state of the AMO. The differences between IPO and AMO’s influence on ocean heat content is that IPO can induces an opposite sign of ocean heat content change between surface and subsurface layers of the ocean, but AMO induces a heat content change in the same sign up to 1500m depth.



By analyzing the ocean heat content changes due to the internal variability in the CESM1 preindustrial control run, it is found that the changes in the phases of the internal climate modes, such as IPO and AMO, can change how the heat is distributed within the ocean. IPO induces a heat content increase in the surface ocean in its positive phase, but a decrease of heat content in the subsurface ocean, vice versa for the negative phase. AMO induces an increased heat content for the entire ocean up to 1500 meter depth in its positive phase, and opposite change in its negative phase.


Aixue Hu
National Center for Atmospheric Research (NCAR)