International satellite to track impacts of small ocean currents

Credit: Pixabay/CC0 Public domain

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

Although climate change causes sea levels to rise over time, researchers also believe that differences in surface height across the ocean can affect Earth’s climate. These ups and downs are associated with currents and eddies, swirling rivers in the ocean, which influence 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’Etudes Spatiales (CNES), with contributions from the Canadian Space Agency (CSA) and the British Space Agency. Launched in November 2022, SWOT will collect ocean height data to study currents and eddies up to five times smaller than previously detectable. It will also gather detailed information about freshwater lakes and rivers.

Observing the ocean at relatively small scales will help scientists assess its role in moderating climate change. The largest storehouse of atmospheric heat and carbon on the planet, the ocean has absorbed more than 90% of the heat trapped by human-caused greenhouse gas emissions.

Much of the continued absorption of this heat – and the excess carbon dioxide and methane that produced it – is believed to occur around currents and eddies less than 100 kilometers in diameter. These flows are small compared to currents such as the Gulf Stream and the California Current, but researchers estimate that, overall, they transfer up to half of the heat and carbon from the surface waters to the ocean depths.

Better understanding this phenomenon may be essential in determining whether there is a ceiling on the ocean’s ability to absorb heat and carbon from human activities.

“At what point does the ocean begin to release massive amounts of heat into the atmosphere and accelerate global warming, rather than limit it?” 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.”

The SWOT mission will collect information on sea level height, which will help scientists study the role of currents in moderating climate change, as well as elevations in freshwater bodies. The mission is being conducted jointly by NASA and CNES, with contributions from UKSA and CSA. Credit: NASA/JPL-Caltech/CNES/Thales Alenia Space

think small

Existing satellites cannot detect smaller-scale currents and eddies, which limits research into how these features interact with each other and with larger-scale flows.

“It’s a place where we’ll learn a lot by having better small-scale observations,” said J. Thomas Farrar, chief science officer for SWOT oceanography at the Woods Hole Oceanographic Institution in Falmouth, Massachusetts.

In addition to helping researchers study the climate impacts of small currents, SWOT’s ability to “see” smaller areas of the Earth’s surface will allow it to collect more precise data along coastlines, where the Sea level rise and the flow of currents can have immediate impacts on land. ecosystems and human activity.

Higher seas, for example, can cause storm surges to penetrate farther inland. In addition, currents intensified by sea level rise can increase saltwater intrusion into deltas, estuaries and wetlands, as well as groundwater supplies.

“In the deep sea, the whole phenomenon of heat and carbon mining will affect humanity for years to come,” said Lee-Lueng Fu, SWOT project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “But in coastal waters, the effects of currents and high seas are felt for days and weeks. They directly affect human lives.

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

The researchers use the height differences between the points, known as the slope, to calculate the movement of the currents. The calculation takes into account the force of gravity of the Earth, which pulls the water up and down, and the rotation of the planet, which, in the northern hemisphere, deflects the flow clockwise. shows around the high points and counterclockwise around the low points. The effect is reversed in the south.

Ocean height is associated with currents and eddies on the ocean surface, which are shown in this visualization based on the period June 2005 to June 2007. SWOT will be able to observe currents and eddies smaller than those illustrated, up to 12 miles (20 kilometers) in diameter. Credit: NASA Goddard Space Flight Center

Current systems hundreds of kilometers wide circulate around vast expanses of ocean. Along the way, smaller currents and eddies break off and interact with each other. When they come together, they carry water from the surface to cooler depths, carrying away heat and carbon from the atmosphere. When these small currents and eddies separate, the water from these cooler depths rises to the surface, ready to absorb heat and carbon again.

This vertical movement of heat and carbon also occurs at the level of the vortices themselves. In the northern hemisphere, clockwise vortices generate downward flows, while counterclockwise vortices create upward flows. The reverse occurs in the southern hemisphere.

Fill gaps

By measuring the height of the oceans down to 0.16 inch (0.4 centimeter) increments, as well as their slopes, the two antennas of SWOT’s Ka-Band Radar Interferometer (KaRIn) will help researchers discern the 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 around 60 miles (100 kilometers) wide. Where the nadir altimeter will point down and take data in one dimension, the KaRIn antennas will tilt. This will allow the KaRIn antennas to scan the surface in two dimensions and, working in tandem, collect data with greater accuracy than the nadir altimeter alone.

“Currently, to get a two-dimensional view from a one-dimensional line, we take all of our one-dimensional lines and estimate what’s going on between them,” said Rosemary Morrow, science lead for SWOT oceanography at the Environmental Studies Laboratory. Geophysics. and Space Oceanography in Toulouse, France. “SWOT will directly observe what is in the gaps.”

Assembly of a satellite to follow water changes in the world from the United States to France

More information:

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Jet Propulsion Laboratory

International satellite to track the impacts of small ocean currents (2022, May 11)
retrieved 12 May 2022

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