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November 10, 2015 | Scientists have long been interested in studying how winds influence ocean waves.
NCAR Senior Scientist Peter Sullivan wanted to examine the relationship in reverse: How do waves affect the atmosphere?
"Most people focus on winds influencing waves because it’s the easiest to study in a laboratory," Sullivan said. "But nature works the other way, too."
The result is this striking 3D animation showing the influence of ocean waves on the air above.
While strong winds from storms create waves on the ocean surface, those waves don’t just stop. They travel away from the storm, sometimes thousands of miles, to areas with lighter winds. There, in those new areas, the waves, which have become swells, influence the atmosphere.
Understanding how this happens provides insight into global weather and climate patterns, as well as into major storms such as hurricanes, which draw energy from the ocean. "With a hurricane, the first thing you see is the fast moving swell created by it," Sullivan said.
Sullivan simulated what would happen if a spectrum of small and big waves moved into an area with light winds. He used a technique called large eddy simulation, first developed by NCAR scientists in the 1960s to account for turbulence in computer models.
A billion data points were crunched by the NCAR-Wyoming Supercomputing Center’s Yellowstone system. NCAR software engineer Scott Pearse later rendered this two-minute visualization from telling chunks of the simulation. "It’s the data that was actually beautiful," Pearse said.
"The ocean wave fields and atmosphere couple, leaving an imprint on each other, and the visualization illustrates some of the complexity of what goes on—in 3D," Sullivan said.
Small waves impose a drag on air, while fast and big waves provide thrust, pushing the air forward. "You can see wave signatures in the atmosphere over a large vertical extent," Sullivan said. (Watch for some of these wave-driven winds aloft between the 1:30 and 2:00 mark in the video).
Sullivan has made available a simplified version of the new software code, and a number of students are using the code for their graduate work.
Pearse created the visualization using a software tool from NCAR called VAPOR, a visualization and analysis platform for ocean, atmosphere, and solar researchers.
When he vacationed in Florida after doing initial work on the project, Pearse found he had gained a new perspective on the relationship between the air and ocean.
"I saw the waves differently," he said. "Now that I know that atmosphere-ocean interaction is a two-way street, I find myself wondering what the air is doing whenever I see moving water."
A journal publication describing the numerical algorithm and further results from the large-eddy simulations can be found at: Sullivan, P.P., J.C. McWilliams and E.G Patton, 2014: Large-eddy simulation of marine boundary layers above a spectrum of moving waves. Journal of the Atmospheric Sciences, doi: 10.1175/JAS-D-14-0095.1
Jeff Smith, Science Writer and Public Information Officer
Physical Oceanography Program at the Office of Naval Research
National Science Foundation
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.