Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) are building a greater understanding of extreme waves in conjunction with climate forecasts.
Using decades of global climate data generated at a spatial resolution of about 25 square kilometers (10 square miles), the researchers were able to capture the formation of tropical cyclones (hurricanes and typhoons) and the extreme waves that they generate. Those same models, when run at resolutions of about 100 kilometers (60 miles), missed the tropical cyclones and the big waves up to 30 meters (100 feet) high.
The findings demonstrate the importance of running climate models at higher resolution, say the researchers. Better predictions of how often extreme waves will hit are important for coastal cities, the military, and industries that rely upon shipping and offshore oil platforms.
Ben Timmermans, a computational scientist at Lawrence Berkeley National Laboratory in Berkeley, California and lead author of the new study said: “The majority of existing models used to study the global climate are run at resolutions that are insufficient to predict tropical cyclones. The simulations in our study are the first long-duration global data sets to use a resolution of 25 kilometers [16 miles]. It’s also the first time a study has specifically examined the impact of resolution increase for ocean waves at a global climatological scale.”
Climate models work by simulating the exchange of air, water and energy between the grid “boxes.” In today’s state-of-the-art climate models, these boxes are typically 100 to 200 kilometers (60 to 120 miles) wide. That level of detail is good enough to catch the formation and movement of mid-latitude storms, the researchers said, because such systems tend to be quite large.
In contrast, tropical cyclones tend to cover a smaller area. While the overall footprint of a hurricane can be broad, the eye of a hurricane can be very compact and well defined, the researchers noted.
To see if the cyclones had an effect on waves, the researchers ran global wave models at both resolutions. They saw extreme waves in the high-resolution model that did not appear in the low-resolution ones.
While additional high-resolution simulations of the future are on the way, the researchers were able to take a first look at possible conditions at the end of the 21st century. The biggest waves in Hawaii are projected to be substantially larger in a much warmer future world, according to the authors.
The researchers added that this study only looked at averages of wind-generated waves. One-off “rogue” or “freak” waves cannot be reproduced in these kinds of models, and large waves such as tsunamis are very different since they are caused by seismological activity, not the wind.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.