PNNL

The Science

The North Atlantic Ocean plays an important role in modulating Earth's climate on decadal to multidecadal time scales by absorbing, releasing, and transporting heat over the planet. These slowly fluctuating sea surface temperatures (SSTs) are often referred to with the term "Atlantic Multidecadal Variability" (AMV).

Scientists remain unsure of how the ocean, the atmosphere, and their interactions generate this variability. Because the interactions are so complex, teasing out the relative roles of ocean, atmosphere, and interactions between them has been difficult.

In a study aimed at isolating the processes driving the AMV, scientists from the U.S. Department of Energy's Pacific Northwest National Laboratory led the development of a powerful climate model methodology to disentangle the coupled ocean-atmosphere interactions in model simulations with full ocean and atmosphere circulations—a fully coupled system. They found that the ocean drove stronger multidecadal variability (greater than 30 years), while the atmosphere drove weaker variability up to interdecadal timescales (10–30 years).

The Impact

The study identified some of the most important atmospheric and ocean processes that produce and damp variations in North Atlantic SSTs. Surface interactions between the atmosphere and ocean decreased the ocean-driven variability because surface heat fluxes acted to damp the ocean-driven SST variability. These results imply that the strength of surface coupling in global climate models might be one of the reasons why many Earth system models simulate weaker AMV compared to observations. This is an important consideration for improving this essential feature of the Earth system in models.

Reference: O.A. Garuba, J. Lu, H.A. Singh, F. Liu, and P.J. Rasch, "On the Relative Roles of the Atmosphere and Ocean in the Atlantic Multidecadal Variability." Geophysical Research Letters 45(17), 9186_9196 (2018). [DOI: 10.1029/2018GL078882].