Fresh Water Feeds Hurricanes’ Fury

Understanding factors influencing a cyclone’s path and intensity improves our ability to forecast and mitigate impacts.

Image courtesy of NOAA
Hurricane Omar.

The Science

DOE scientists at Pacific Northwest National Laboratory found that tropical cyclones intensify considerably when passing over ocean regions with a barrier layer.

The Impact

Understanding the environmental factors that influence a cyclone’s path and intensity improves our ability to forecast tropical cyclones and to mitigate their destructive potential.


A barrier layer in ocean environments, or Mixed Layer Depth, is defined as the depth where the density increases from the surface value due to a prescribed temperature decrease of some value (e.g., 0.2°C) from the surface value while maintaining constant surface salinity value. Using a combination of observations and model simulations, the team demonstrated that barrier layers, formed through high fresh water input reducing the salinity in the upper tropical oceans, significantly increase the intensity of tropical cyclones. When tropical cyclones pass over these regions, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. Their findings underscore the importance of observing salinity structure in deep tropical barrier layer regions.  As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.


Dr. Ping Chang
Texas A&M University


Basic Research: DOE Office of Science, Office of Biological and Environmental Research


Balaguru K, P Chang, R Saravanan, LR Leung, Z Xu, M Li and JS Hsieh. 2012. “Ocean Barrier Layers’ Effect on Tropical Cyclone Intensification.” Proceedings of the National Academy of Sciences, U.S.A., vol. 109 no. 36 14343-14347. DOI:10.1073/pnas.1201364109.  

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