Ocean eddies in the climate system: Disentangling the role of mesoscale eddies in atmosphere-ocean interactions and global climate variability

The multifaceted role of oceanic mesoscale eddies in the coupled climate system remains a focus of scientific discussion and research. In this study, we present a set of simulations utilizing the same model and resolution to disentangle the role of mesoscale eddies for global and local climate by applying an eddy backscatter parameterization to enhance or suppress eddy variability.

 Mesoscale eddies can be seen as the oceanic high- and low-pressure systems, acting as drivers of ocean weather by introducing chaotic small-scale features into the large-scale flow. By redistributing heat, momentum, and tracers such as nutrients or dissolved trace gases, they influence and shape ocean circulation patterns and affect marine productivity through vertical mixing. Eddies also interact with the atmosphere, modulating heat and moisture exchange, which contributes to variations in wind patterns, storm tracks, and ultimately influences regional and global climate dynamics.

 In this study, we conduct three distinct sets of ensemble simulations using the AWI-CM3 climate model to investigate the impact of ocean weather on climate variability. All configurations use the same spatial resolution but different levels of eddy activity due to different parameterization calibrations. One configuration is largely resolving the eddy variability, one simulation is substantially suppressing it and a reference configuration is somewhere in between using standard model parameters for AWI-CM3. With a resolution of 30 km in the atmosphere and 10–60 km in the ocean, these simulations are sufficiently detailed at the coupling interface to directly resolve air-sea interactions at the feature level. The ensemble simulations span the period from 1950 to 2015. They are then used to study the effect of eddy activity on long-term variability in large-scale ocean and atmospheric dynamics. A special focus is on mesoscale atmosphere-ocean interactions along eddy active regions such as the western boundary currents, highlighting substantial changes in local heat fluxes as well as large-scale dynamics, both in terms of climatic means and temporal variability and including changes in, e.g., Gulf Stream position and strength and its consequences for the atmospheric circulation.