Deep Cyclones and Benthic Storms in the Western North Atlantic: New Insights From a Regional Circulation Model

Deep cyclones (DCs) are mesoscale, deep‐reaching features that develop near meander troughs of large‐scale currents, such as the Gulf Stream. Although, in some aspects, they could be viewed as oceanic analogs of synoptic‐scale cyclones in the mid‐latitude atmosphere, their dynamics and impacts are not fully understood. Notably, the roles of different vorticity sources in deep cyclogenesis and the relationship of DCs with “benthic storms” remain to be elucidated. Here we develop a regional configuration of a primitive‐equation model with 1/20° horizontal resolution and 10‐m vertical resolution over the entire water column to study DCs in the western North Atlantic. In our simulation, DCs form both in the Hatteras Abyssal Plain, where DCs were observed during the 1980‐90s SYNOP campaign, and in the Sohm Abyssal Plain, where observations are lacking. Their spatial scales, lifetimes, pressure drops, swirl velocities, and drift speeds compare favorably with observational estimates. During deep cyclogenesis, the pressure fall at abyssal depth reflects a small imbalance between the effects of the sea level drop and of the density increase in the overlying water column within tightening meander troughs. Below 1,500 m, the main source of cyclonic vorticity is vortex stretching, associated mainly with the curvature‐induced ageostrophic flow, while vortex tilting is a sink of smaller magnitude. Near‐bottom currents in DCs reach speeds comparable to those observed during benthic storms and, when present, dominate the basin‐scale bottom energy dissipation. Overall, the study highlights the importance of DCs for sub‐annual variability and material transport in the abyssal interior.