Researchers from Fudan University, Shanghai, China have been using MITgcm to explore leakage in cyclonic and anticyclonic mesoscale eddies.

Reporting by Helen Hill for MITgcm

In a recent study published in Geophysical Research Letters, oceanographers Yanjiang Lin and Guihua Wang have uncovered a striking asymmetry in how cyclonic and anticyclonic mesoscale eddies leak water and particles into the surrounding ocean. Their research, titled “Divergent Leakage Features of Anticyclonic and Cyclonic Mesoscale Eddies,” offers a new perspective on how these swirling oceanic structures redistribute mass, energy, and even biological material across the global ocean. Central to their investigation was the use of the MIT General Circulation Model (MITgcm), the numerical tool that allowed the team to simulate and analyze the fine-scale dynamics of eddy leakage with unprecedented clarity.

Mesoscale eddies—large, swirling water masses that can span hundreds of kilometers and persist for weeks to months—are known to play a crucial role in transporting heat, salt, nutrients, and even microplastics and fish larvae across ocean basins. While their ability to trap and carry water is well documented, the mechanisms by which water escapes or “leaks” from these eddies have remained less understood. Lin and Wang’s study challenges the long-standing assumption that cyclonic (counterclockwise in the Northern Hemisphere) and anticyclonic (clockwise) eddies behave similarly in this regard.

By analyzing global drifter trajectories and conducting high-resolution simulations with MITgcm, the researchers discovered that eddy leakage is not symmetric. In the Northern Hemisphere, drifters tend to exit anticyclonic eddies from the rear-left side and cyclonic eddies from the rear-right side, relative to the eddy’s direction of motion. This pattern reverses in the Southern Hemisphere. The team traced this behavior to the presence of narrow “potential vorticity (PV) channels” along the edges of eddies—regions where the fluid’s rotational properties create pathways for particles to escape.

To explore the physics behind these PV channels, Lin and Wang turned to MITgcm. The model allowed them to simulate idealized eddies under controlled conditions, isolating the effects of rotation, stratification, and background flow. Through these simulations, they observed that particles near the eddy margins consistently exited through PV channels that aligned with the direction opposite to the eddy’s rotation. This behavior was driven by the relative vorticity gradient—essentially, how the spin of the water changes across the eddy—which differs between cyclonic and anticyclonic systems.

MITgcm’s flexibility and high-resolution capabilities were critical to the success of the study. The model enabled the researchers to resolve fine-scale features at the eddy boundary that are typically missed in coarser global models. It also allowed them to test a range of eddy strengths, sizes, and background conditions, confirming that the divergent leakage behavior was robust across different oceanic settings.

The implications of this work are far-reaching. Understanding how and where eddies leak water helps scientists better predict the transport of heat and biogeochemical tracers in the ocean. It also informs models of how pollutants, nutrients, and biological organisms disperse—key knowledge for fisheries, climate science, and marine conservation.

Lin and Wang’s findings underscore the importance of combining observational data with advanced modeling tools like MITgcm to unravel the complexities of ocean dynamics. Their study not only deepens our understanding of mesoscale eddies but also opens new avenues for exploring how small-scale processes shape the large-scale behavior of Earth’s oceans.

To find out more about this work​ contact Guihua

Story image: Float tracks from figure 1 of Lin and Wang (2025)

About the Researchers

Guihua Wang (left) is a Professor in the Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Science, at Fudan University in China. His research centers on multi-scale ocean-atmosphere interactions and their role in the ocean. He carries out both observing and modeling studies covering all three major oceans, especially the Pacific, including the South China Sea. His group has been using MITgcm since 2019. Yanjiang Lin (right) is a postdoc in Guihua Wang’s group. To find out more about Wang Group research email Guihua [wanggh@fudan.edu.cn]

 

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