International satellite to track effects of small ocean currents – Verve times

The Surface Water and Ocean Topography mission will examine how the ocean absorbs atmospheric heat and carbon, mitigating global temperatures and climate change.

While climate change drives sea level rise over time, researchers also believe that differences in surface elevation from place to place in the ocean can influence Earth’s climate. These highs and lows are associated with currents and eddies, swirling rivers in the ocean, which affect how it absorbs atmospheric heat and carbon.

Enter the Surface Water and Ocean Topography (SWOT) mission, a joint effort of NASA and the French space agency Center National d’Études Spatiales (CNES), with contributions from the Canadian Space Agency (CSA) and the United Kingdom Space Agency. Launching in November 2022, SWOT will collect data on ocean heights to study currents and eddies up to five times smaller than previously detectable. It will also collect detailed information on freshwater lakes and rivers.

By observing the ocean on a relatively small scale, scientists can assess its role in mitigating climate change. The ocean, the largest storehouse of atmospheric heat and carbon in the world, has absorbed more than 90% of the heat retained by man-made greenhouse gas emissions.

Much of the continued uptake of that heat — and the excess carbon dioxide and methane it produced — would take place around currents and eddies less than 100 kilometers across. These currents are small compared to currents like the Gulf Stream and the California Current, but researchers estimate that in total they transfer up to half the heat and carbon from surface waters to the ocean depths.

A better understanding of this phenomenon may be key to determining whether there is a ceiling to the ocean’s ability to absorb heat and carbon from human activities.

“What’s the turning point at which the ocean starts releasing massive amounts of heat back into the atmosphere and accelerating, rather than limiting, global warming?” said Nadya Vinogradova Shiffer, SWOT program scientist at NASA headquarters in Washington. “SWOT can help answer one of the most critical climate questions of our time.”

think small

Existing satellites cannot detect smaller currents and eddies, limiting research into how those features interact with each other and with larger currents.

“That’s a place where we’ll learn a lot from better observations of the small scales,” said J. Thomas Farrar, an oceanography SWOT scientist at the Woods Hole Oceanographic Institution in Falmouth, Massachusetts.

In addition to helping researchers study the climate effects of small currents, SWOT’s ability to “see” smaller areas of the Earth’s surface will allow for more accurate data collection along coastlines, where rising ocean levels and the flow of currents have immediate effects on the land may have ecosystems and human activity.

For example, higher seas can cause storm surges to penetrate further inland. Also, currents enhanced by sea level rise can increase the intrusion of saltwater into deltas, estuaries and wetlands, as well as groundwater supplies.

“In the open ocean, the whole phenomenon of pulling down heat and carbon will affect humanity for years to come,” said Lee-Lueng Fu, the SWOT project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “But in coastal waters, the effects of currents and sea level can be felt for days and weeks. They directly affect people’s lives.”

So how will measuring ocean height lead to a better understanding of currents and eddies?

Researchers use elevation differences between points — known as slope — to calculate the movement of currents. The math explains the Earth’s gravity, which pulls water from high to low, and the planet’s rotation, which in the Northern Hemisphere bends the current clockwise around high points and counterclockwise around low points. In the south, the effect is reversed.

Stream systems hundreds of miles wide flow around vast oceans. Along the way, smaller currents and eddies spin away and interact with each other. When they converge, they drive water from the surface down to colder depths, taking heat and carbon from the atmosphere. When those smaller currents and eddies flow apart, water from those colder depths rises to the surface, ready to absorb heat and carbon again.

This vertical movement of heat and carbon also occurs at vortices themselves. In the Northern Hemisphere, clockwise vortices generate downward currents, while counterclockwise vortices create upward currents. The reverse occurs in the Southern Hemisphere.

Fill in the gaps

By measuring ocean heights up to 0.16 inches (0.4 centimeters), as well as their slopes, SWOT’s two Ka-band Radar Interferometer (KaRIn) antennas will help researchers discern currents and eddies as small as 12 miles (20 kilometers) across. .

SWOT will also use a nadir altimeter, an older technology that can identify currents and eddies up to about 100 kilometers across. Where the nadir altimeter points straight down and records data in one dimension, the KaRIn antennas will tilt. This allows the KaRIn antennas to scan the surface in two dimensions and, in tandem, collect data with greater precision than the nadir altimeter alone.

“Now to get a two-dimensional picture of a one-dimensional line, we take all our one-dimensional lines and estimate what’s happening between them,” said Rosemary Morrow, a SWOT scientific chief of oceanography at Laboratoire d’Études and Géophysique et Océanographie Spatiales in Toulouse. , France. “SWOT will directly observe what is in the holes.”

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