The Ocean or the Atmosphere: Diagnosing Forced Versus Intrinsic Low-Frequency Variability in an Idealized North Atlantic Ocean-Atmosphere Model

The ocean or the atmosphere - that is the question. Or at least one of the questions when it comes to intrinsic versus forced low-frequency variability in the climate system, i.e. does the ocean or the atmosphere play a more dominant role in our climate? In an effort to help answer this question, we investigate the dynamics of the ocean-atmosphere system in the frequency domain, using the idealized Quasi-Geostrophic Coupled Model optimized to run in the North Atlantic Ocean. The model consists of a box ocean coupled to a channel atmosphere via mixed layers that allow for the vertical exchange of heat and momentum across the ocean-atmosphere boundary. In the frequency and wavenumber domains, we compute spectra and spectral transfers, the latter indicating the relative importance of the forced versus intrinsic contributions to the maintenance of low-frequency variability. We run the model in three distinct modes: a dynamic atmosphere only, a dynamic ocean only, and a fully coupled dynamic ocean-atmosphere regime. This analysis on a simplified model provides a better understanding of the source of energy at low frequencies within the climate system, and will help contribute to future studies using more complex models.