NASA’s S-MODE field campaign is deployed in the Pacific Ocean

When the research vessel Bold Horizon set sail from Newport, Oregon, in early October, it joined a small armada of planes, drones and other high-tech devices chasing the physics of changing ocean shape.

NASA’s Sub-Mesoscale Ocean Dynamics (S-MODE) experiment is converging on a stretch of sea 110 nautical miles off the coast of San Francisco. Over the course of 28 days, the team will deploy a new generation of instruments to observe eddies, currents and other dynamics at the air-sea interface. The goal: to understand how these dynamics drive the exchange of nutrients and energy between the ocean and atmosphere and ultimately help shape Earth’s climate.

Perhaps the most familiar “sub-mesoscale” features are the phytoplankton-rich eddies or eddies that can be seen spiraling across the ocean from Earth’s satellites.

“Some of the coolest pictures of submesoscale eddies in the ocean come from the Apollo spaceflight photos,” said Tom Farrar, a scientist at Woods Hole Oceanographic Institution in Massachusetts and principal investigator of S-MODE.

Such objects are difficult to analyze because they cover up to 6.2 miles (10 kilometers) farther than any ship, but smaller than regions typically studied by satellite measurements. Filled with energy, they can change in a matter of hours. Farrar says researchers’ ability to simulate these dynamics on computers has outpaced their ability to combat them at sea — until recently.

This work is important because, although the surface layer makes up only about 2% of the ocean, it plays a huge role in the climate system. It is there, at the air-sea boundary, that nutrients, gases and heat are exchanged – this process is called vertical exchange.

The process is not fully understood, and S-MODE observations may help reconcile differences between current models. The implications for climate science are significant. According to some estimates, the net effect of submesoscale eddies on vertical heat transfer is an order of magnitude greater than planetary energy imbalance associated with greenhouse effect.

Tracking the surface of the ocean

From the belly of a King Air B200 at NASA’s Armstrong Flight Research Center in Edwards, Calif., protrudes an instrument that Farrar calls one of the stars of the mission. From its perch 28,000 feet (8.5 kilometers) in the air, DopplerScatt uses radar to bounce electromagnetic energy from the wind the surface of the ocean and measure the energy dissipated.

The instrument, developed at NASA’s Jet Propulsion Laboratory in Southern California, can simultaneously map surface currents and wind. “With the help of S-MODE, we are trying to observe two things at the same time: how the ocean moves and how the ocean and atmosphere interact and influence each other,” said Nadya Vinogradova Schiffer, S-MODE program researcher and Phys. oceanography program manager at NASA headquarters in Washington.

The team relies on state-of-the-art weather forecasting to identify severe wind conditions because the radar can’t “read” calm, flat seas, said Dragana Perkovic-Martin, JPL’s DopplerScatt principal investigator. “The glossy sea surface creates a very weak radar signal. We need the wind to disturb the surface and produce the signal we’re looking for,” she added. “Participating in a mission of this magnitude can be exciting and nerve-wracking.”

On board another plane is an instrument that can display microscopic marine life in billions of colors. JPL’s Portable Remote Spectrometer (PRISM), which resembles a metal basketball, will be inside the Gulfstream III aircraft, observing phytoplankton blooms in hundreds of wavelengths from ultraviolet to infrared.

By tracking chlorophyll, a prominent signature of these algae, PRISM will help scientists visualize ecology interacting with ocean currents, providing exponentially more information than the familiar three-channel (red, green, blue) cameras. It will also inform the next day’s flight planning during the campaign, said David Thompson, JPL’s principal investigator for PRISM.

“PRISM is one of our eyes that looks for submesoscale features across the ocean,” he said. “The mission is incredibly interdisciplinary, and we’re all rallying around this tool.”

For the crew below on Bold Horizon, life aboard a research vessel traveling at 5 mph can seem cramped and full of adventure. “It’s fun, but it’s fun, like camping or climbing a mountain,” Farrar said.

Problems can be unpredictable. Last year’s pilot launch overcame delays related to COVID-19 and a rogue wave that disabled several wave gliders — surfboard-like marine robots equipped with scientific instruments.

In the second of three deployments, the mission plans to collect more than 15 data sets, ranging from biology to atmospheric weather. The data will complement another NASA mission that will launch later this year. The Surface Water and Ocean Topography, or SWOT, satellite will survey nearly all of Earth’s water in higher definition than before.

“The ocean is turbulent at all spatial scales, and there are many insights that can be gained by taking these measurements together,” Farrar said. “NASA has played a major role in oceanography and continues to push the boundaries of what we understand about Earth.”

The third and final deployment of S-MODE is scheduled for next spring.