Exploring the Ocean’s Depths with a New Hyperwall Visualization Tool

At a depth of 850 meters near the coast of Antarctica (140 - 130° W longitude), previously undiscovered eddies become apparent in a new visualization of a global ocean simulation run on the Pleiades supercomputer. Relative salinity is shown in grayscale, with the darker areas showing slightly lower salt concentrations. At bottom, the continental shelf is shown in red, and the ice-covered land is shown in white. The video is running at 6 days of simulation time per second.
Bron Nelson, David Ellsworth, NASA/Ames

August 2, 2017

Scientists from the Estimating the Circulation and Climate of the Ocean (ECCO) project were glowing with excitement during two recent day-long sessions using the hyperwall at the NASA Advanced Supercomputing (NAS) facility, located at Ames Research Center in Silicon Valley. It was their first opportunity to try a new, interactive method of viewing output from a groundbreaking ECCO simulation carried out on the Pleiades supercomputer during the past two years.

With their high-resolution global ocean simulation spread out across the hyperwall’s 128 screens, Dimitris Menemenlis of NASA’s Jet Propulsion Laboratory and Christopher Hill of the Massachusetts Institute of Technology (MIT) noticed some unusually persistent and symmetric eddies circulating at a depth of 850 meters near the coast of Antarctica. The new capability developed by the NAS data analysis and visualization team enabled the researchers to discover these unusual features, which had not been noticed during previous analyses of the simulation.

"In the global view, the eddies jumped out at us right away, because they were so different from everything else we could see happening across the ocean," said Menemenlis.

Diving into Petabytes of Data

First run on Pleiades in 2014, the ECCO team’s simulation remains to this date the highest resolution global ocean configuration ever achieved with the MIT general circulation model (MITgcm), a widely used ocean modeling code. The simulation has 90 vertical levels, and horizontal grid spacing that ranges from 750 meters around Antarctica to 2.3 kilometers at the equator, resulting in 22 billion model grid points. Due to the size and complexity of the data—over 4 petabytes of time-evolving, multi-property model output—the researchers were previously unable to look at full-resolution global views of the simulation. They could only visualize small subsets of the model output at any one time.

"If we were looking for a specific feature in a particular region of the ocean, we could find it by exploring that part of the simulation in great detail," Menemenlis said. "But in the global view, we could not see everything in detail at the same time. So, if we were not already looking for something, we had no way of knowing it was there," he explained.

photo of Dimitris Menemenlis and Chris Hill at the NAS hyperwall — ECCO researchers Dimitris Menemenlis (left) and Christopher Hill take a closer look at a new visualization of their global ocean simulation on the hyperwall at the NASA Advanced Supercomputing facility. *David Ellsworth, NASA/Ames*

For this reason, the researchers missed some ocean features and processes, like the unusual Antarctic eddies, that were in the simulation all along. But now, the updated visualization tool provides a high-resolution view of the whole globe at once, enabling them to easily spot new things. “And once we see them, we can examine them in detail just by walking closer to the screen,” said Menemenlis.

Once the researchers got a closer look at the Antarctic eddies, another feature of the new tool came into play. The NAS team adjusted the hyperwall view so that instead of showing the global ocean circulating across all 128 screens, each screen quickly changed to display a single region—just the area containing the eddies. Progressively deeper levels of the region were shown from left to right across the wall, with properties such as temperature, surface wind stress, density, and salinity clearly identified with high-contrast colors that could be changed on the fly.

Even better, multiple properties could be combined in a single view as time progressed, enabling the scientists to quickly determine whether the properties might be correlated.

To achieve this, the NAS team took advantage of the high-capacity network bandwidth, exceptional data processing capabilities, and 245-million-pixel display of the hyperwall, one of the world’s most powerful visualization systems. They significantly improved performance by using compression to enable viewing at 24 frames per second, and integrated a mechanism to display time-evolving scatter plots, which allowed them to display the distributions of individual properties as they change over time.

Menemenlis was enthusiastic. "This tool completely transforms the way we study the global ocean circulation. Not only can we can discover processes taking place in the simulation, but we can immediately investigate them to determine their causes."

Speeding Up the Pace of Discovery

Back in the hyperwall room, the scientists and the visualization team worked together for hours, interactively exploring the dataset and making several more discoveries. The origin of the unusual eddies near Antarctica did not remain a mystery for long: above them, large cracks in the sea ice and cold air cause more ice to form, which rejects salt and increases the salinity of the surrounding water. The resulting dense blobs of water sink and spread, and Earth’s rotation causes them to spin.

"The eddies may or may not have any effect on the larger ocean system," Menemenlis said. "But they are interesting—and, if we hadn’t found them, we would have had absolutely no chance of finding out whether they are important in a global sense."

A new tool developed at NAS provides researchers with a global view of their ocean simulation in high resolution. In this part of the global visualization, the Gulf Stream features prominently; surface water speeds are shown ranging from 0 meters per second (dark blue) to 1.25 meters per second (cyan). The video is running at one simulation day per second. Bron Nelson, David Ellsworth, NASA/Ames

The ECCO team studies global ocean circulation in order to better understand how the ocean interacts with the atmosphere, sea ice, and ice sheets, and to investigate ocean ecology and the carbon cycle: 12 times more active carbon is stored in the ocean than in the air, vegetation, and soil combined. Learning more about how all of these complex processes work together helps us understand our planet’s climate and weather, and how both are changing.

Their simulations are used in combination with data obtained from Earth-observing satellites and other observations, and help engineers design satellite missions such as the upcoming Surface Water Ocean Topography (SWOT). For example, by discovering the surface signatures of internal ocean processes in the simulations, the researchers can provide parameters that help SWOT designers calibrate their instruments to detect these signatures.

Eventually, the ECCO team hopes to couple their high-resolution ocean model with a global atmospheric model of similar resolution being developed at NASA’s Goddard Space Flight Center. This would be a monumental achievement that would revolutionize our understanding of how Earth’s atmosphere interacts with the sea.

—Michelle Moyer, NASA Ames Research Center