Diagnosing Energy and Heat Transfer in the North Atlantic Region of Idealized and Realistic Ocean-Atmosphere Models: A Frequency-Domain Approach

The ocean and atmosphere, two major components of the climate system, are inherently coupled, and there is long-standing interest in deciphering whether oceanic and atmospheric variability is primarily due to intrinsic processes driven by nonlinear advection, due to forcing from the other fluid, or due to the inherently coupled nature of the ocean-atmosphere system. In this work, we investigate the oceanic, atmospheric, and coupled sources of variability by calculating the frequency-domain spectral energy and temperature variance budgets of an idealized, eddy-resolving, ocean-atmosphere model tuned to mimic the North Atlantic, and we compare these idealized results with results from the Community Earth System Model. This spectral diagnostic is well-suited to study energy and heat transfer, as it identifies the terms that contribute to the input and removal of energy and heat across a range of timescales, from one day to 100 years. The energy budget analysis, which takes into account the mechanical coupling between fluids, reveals that the intrinsic nonlinear advection of kinetic energy is the dominant source of decadal and interdecadal variability in both fluids. We further find that the sources and sinks of energy vary across different ocean regions, and find that the western boundary current separation is a preferred region of energy input, while energy removal is primarily found along the western boundary of the basin. Here, we add to the story by investigating the temperature variance equations, which are associated with the thermal coupling between fluids.