How Ocean Eddies Influence the Intensity of Tropical Cyclones

Tropical cyclones form in regions with high sea surface temperatures and are then driven across the ocean by atmospheric currents. How strong they become depends, among other things, on the conditions they encounter along the way. In general, warm sea surfaces continue to feed energy to the cyclone, while lower water temperatures weaken it. Thus, mesoscale ocean eddies, which can be up to 100 kilometers in size and involve either warm water rotating in cooler water masses or cooler water rotating in warmer waters, can exert a significant influence on the intensity of tropical cyclones. Researchers have already demonstrated this for individual storms—for example, in the case of the devastating Hurricane Katrina, which intensified rapidly over a warm ocean eddy and then weakened over a cold eddy before hitting the US coast in August 2005. However, a systematic and statistical analysis of these interactions on a global scale has been lacking until now.

A study conducted at the Max Planck Institute for Meteorology has revealed, for the first time, the extent to which ocean eddies influence the strength of tropical cyclones on average across the globe using a global storm- and eddy-resolving configuration of the ICON model. In a one-year simulation with a resolution of five kilometers in the ocean and atmosphere, researchers Arjun Kumar, Nils Brüggemann, and Jochem Marotzke analyzed the tropical cyclone tracks over the turbulent world ocean.

“It is not just sometimes that cyclones encounter one or more mesoscale ocean eddies, but in fact it is very common,” says Arjun Kumar, lead author of the study.

The analysis clearly shows that if a cyclone passes over a larger number of cold than warm ocean eddies, it intensifies less quickly on average and also remains weaker overall. Conversely, there is also evidence that cyclones that encounter more warm than cold ocean eddies tend to intensify more quickly and are stronger overall than those that predominantly encounter cold eddies. However, according to the authors, simulations over longer periods of time are needed to verify the second finding.