Diagnosing Submesoscale Divergence From Sea Surface Height

Abstract The Surface Water and Ocean Topography satellite mission now delivers global sea surface height (SSH) observations at scales fine enough to resolve submesoscale eddies (<50 km). At these scales, the traditional geostrophic approximation, commonly used to infer surface currents from SSH, no longer holds. Here, we present a new dynamical framework that diagnoses ageostrophic currents and, in particular, divergent motions directly from SSH. The framework is trained and validated using a high‐resolution numerical simulation of a western boundary current system, where submesoscale eddies are the most energetic. This approach highlights the unique capability to reveal vertical motions in the upper ocean from SSH, allowing for diagnosing transport of heat, carbon, oxygen, and nutrients between the surface and the interior of the ocean.