Morphology of atmospheric convective systems facilitates rapid transmission of near-inertial energy into the ocean thermocline

Near-inertial internal waves (NIWs) are among the primary drivers of turbulence that sustains the ocean stratification. To propagate downward into the ocean interior, NIWs typically need horizontal scales L∼100 km. Therefore, it is commonly held that NIWs generated by basin-scale midlatitude storms depend on refraction by background vorticity gradients to become horizontally compact and then propagate into the thermocline. This contrasts with NIWs generated by tropical cyclones (TCs), which can rapidly propagate downward regardless of background ocean conditions. Here, we study the upper ocean response to midlatitude storms and TCs using a dynamical framework whose equations of motion are written in terms of vorticity and divergence rather than velocity vectors. We show that patterns of wind stress curl and convergence that are inherently linked to atmospheric convection necessarily generate NIWs that are horizontally compact and can induce substantial downward energy fluxes within the first inertial cycle after storm passage. The vorticity-divergence dynamical framework elucidates this because it allows us to account for spatial wind patterns even when solving motion linearly and for a single point in space. With this, we argue that the morphology of mesoscale convective systems allows them to drive downward propagation of NIWs in their wakes, whether ocean storms take the shape of a TC or a midlatitude storm.