Submesoscale Dynamics over the Continental Shelf: Drivers and Implications for Across-Shelf Exchange

Recent advancements in remote sensing of oceanic surface currents have observed dramatic examples of both persistent and transient small-scale O(2-20km) circulation features in proximity to the coast. With horizontal length scales similar to the internal deformation radius, and Rossby numbers O(1), coherent vortices and frontal features represent a class of lateral exchange processes that are not well characterized within the coastal ocean. Previous efforts focused on the inner part of the shelf have suggested that coastal mesoscale and submesoscale dynamics can have a significant impact on exchange budgets between the nearshore and the rest of the shelf. Heat, salt, and momentum budgets of broad shelves such as the Middle Atlantic Bight (MAB) have uncertainties that suggest unresolved across-shelf eddy heat fluxes. Additionally, the temporal and spatial scales of eddy diffusivity, a primary indicator of mixing and exchange are not well constrained in coastal environments. along broad and shallow shelves.

The potential influence of bottom stress, topography, winds, and tides on coastal submesoscale features are both distinct from open ocean submesoscale dynamics and purely bathymetrically forced features as well as poorly understood. These features are also difficult to resolve in existing coastal observing systems. This work seeks to observe and diagnose the coastal mesoscale and submesoscale dynamics over the middle part of the New England Shelf (NES), identifying their role in driving exchange across the shelf. Utilizing a novel implementation of HF radar to resolve horizontal scales of 2 km up to 90 km offshore, combined with in situ sampling of these features by both fixed, moored, and mobile platforms over multiple seasons, this work explores the seasonally varying effects of small scale features on exchange across the shelf. Initial results from the project effort are presented here.