Submesoscale coherent vortices (SCVs), which are still not resolved in climate models, can be long-lived structures that influence the global distribution of heat and other tracers. SCVs are commonly generated by the separation of slope-boundary currents, where the subsequent instability of vortex filaments leads to the formation of coherent structures. Although this process can be symmetric, most observed SCVs are anticyclonic.

Here, we use a high-resolution numerical simulation (GIGATL1) and an eddy-tracking algorithm based on the potential vorticity anomaly to study the SCV population near the Mid-Atlantic Ridge (MAR) on the 27.8 isopycnal surface (~2100 m depth). Our region of study is close to the Equator, where the local Coriolis frequency is relatively low, with a noticeable influence on vortex dynamics. We analyze the statistics of SCVs, including their intensity, size, shape, lifetime, polarity, propagation speed, and direction.

Our results indicate that cyclonic SCVs are more numerous than their anticyclonic counterparts and can be equally long-lived (up to several hundred days). However, the largest SCVs are predominantly anticyclonic. We find that these large anticyclones are more likely to propagate away from the MAR than cyclonic vortices. We hypothesize that this polarity bias arises from the enhanced ability of anticyclones to merge and to remain coherent under adverse strain in the turbulent eddy field. The emergence of these large and long-lived anticyclones therefore leads to a higher probability of detection compared with cyclones.