Discovering dominant atmospheric drivers of ocean variability

What are the origins and pathways of stochastic variability in the ocean? Here I will describe a new method, leveraging tools from parameter estimation and data assimilation, for combining ocean model dynamics with historical estimates of air-sea fluxes to discover atmospheric modes optimized to excite the ocean. I will use this approach to infer dominant drivers of variability in the North Atlantic Subpolar Gyre and the Atlantic Meridional Overturning Circulation using the adjoint of the MITgcm and fluxes from the ECCO ocean state estimate. Our analysis collapses the space of potential atmospheric patterns onto a subset -- in this case, principally associated with the North Atlantic Oscillation -- that dominate interannual ocean variability. Using perturbation experiments, we illustrate the pathways along which variability propagates from the atmosphere to the ocean in a nonlinear ocean model. This technique is applicable across a range of problems across Earth System components, including in the absence of a model adjoint.