by Staff Writers
Pasadena CA (JPL) Aug 14, 2017
This past week marks the 25th anniversary of the launch of a revolutionary ocean research vessel - a space "ship." As the NASA/CNES Topex-Poseidon satellite ascended into orbit, it ushered in a new era of oceanography with the first highly accurate, global measurements of sea levels.
That mission and its three successors, all named Jason, have continuously mapped global ocean currents and tides; opened our eyes to the global reach of El Nino and other climate events; created a quarter-century-long, extraordinarily precise record of global and regional sea level rise; and enabled improved forecasts of extreme weather events such as hurricanes, floods and droughts.
A new slideshow celebrates this important data set - a fundamental measurement for the study of the oceans and climate - and the longstanding U.S.-French collaboration that brought it about.
Our planet's oceans are too vast and complex to be fully measured by any single satellite, or even by any single nation. Topex-Poseidon and its successor Jason satellite missions are shining examples of the power of a sustained, long-term international partnership, led by the U.S. and French space agencies, NASA and CNES.
For nearly three decades, NASA and CNES scientists and engineers have pooled their expertise, talents and insights to design and construct an integrated spaceborne measurement system far more powerful than the sum of its parts. NASA and CNES have worked together, applying advanced technology to collect measurements of remarkable precision and accuracy, and then making those measurements freely and openly available. With this effort, they have provided humanity with unprecedented views of the global oceans, how they change on time scales of days to decades, and how the oceans influence - and respond to - weather and climate.
"For more than a generation, NASA and CNES scientists and engineers have collaborated to make exquisitely accurate measurements of the ocean surface from space, providing insights into the workings and interactions of our planet's two great fluid systems, the oceans and the atmosphere," said Michael Freilich, director of NASA's Earth Science Division in Washington.
Large-scale currents like the Gulf Stream tend to flow along contours of constant ocean height, following the sides of the hills and valleys. The steepness of a slope indicates the speed of the current. Unlike terrain on land, however, the liquid "landscape" shifts with changes in winds, temperature and other factors, causing shifts in the locations and speeds of the currents. The only way to monitor these changes over the entire surface of Earth's ocean is to make precise measurements of the height of the ocean surface from orbiting satellites.
Measuring the ocean shape over nearly the entire globe every 10 days, Topex-Poseidon gave the first quantitative view of how ocean currents change with the seasons. Topex/Poseidon and the Jason-1, Jason-2 and Jason-3 missions have provided unique insights into how ocean circulation affects climate by moving heat from place to place on our planet.
Heat Storage in the Ocean
"As human-caused global warming drives sea levels higher and higher, we are literally contributing to the reshaping of the surface of our planet," said Josh Willis, NASA project scientist for Jason-3 at NASA's Jet Propulsion Laboratory in Pasadena, California. "The precision altimetric satellite missions tell us how much and how fast."
El Nino, La Nina, and More
Lee-Lueng Fu of JPL - project scientist for the first two ocean altimetry missions - pointed out, "Topex-Poseidon allowed us to follow their evolution and showed that these events weren't limited to just the tropics. It also gave us evidence of even longer-lasting ocean variations." One of these is the Pacific Decadal Oscillation, similar to El Nino and La Nina in character but with phases lasting up to several decades.
In the last 25 years, with the help of altimetry data, scientists have pinpointed many global connections between these multi-year ocean variations and weather consequences such as drought and flooding throughout the globe. While these events have by no means yielded all their secrets, they are better understood and better forecast than before global spaceborne observations began.
Tides on the Open Ocean
So far, each of the ocean altimetry missions has proven to be long-lived. Topex-Poseidon was eventually decommissioned in 2005 after 13 years in orbit. Jason-1 survived almost 12 years, until July 2013. Nine-year-old Jason-2 and Jason-3 (launched in January 2016) are still in operation.
In 2014, an unexpected forecasting use for altimetry data became operational. Bangladesh, whose 46-year history has encompassed death-dealing river floods, uses Jason-2 measurements of river levels in its flood forecasting and warning system. Within the first year using these data, Bangladesh's system enabled the most accurate, long-lead flood warnings ever given for that nation.
A New Role for Jason-2
Besides protecting Jason-3, the new orbit will allow Jason-2 to produce an improved, high-resolution estimate of Earth's average sea surface height. Because ocean topography is partly determined by the contours on the ocean bottom, the estimate is expected to enable scientists to improve maps of the seafloor, resolving currently unknown details of underwater features such as seamounts. These maps will permit advances in ocean modeling, tsunami wave forecasting and naval operations support.
Into the Future
Satellites have already revolutionized oceanography, and soon they will do the same for hydrology - the study of water on land. The French/U.S. Surface Water and Ocean Topography (SWOT) mission will be at the forefront, carrying an innovative interferometer dubbed KaRin that marks a break with today's technologies.
Fu notes that these changes show the value the world scientific community places on the ocean altimetry program. "The measurement is so important, and the technology is fully demonstrated," he said. "In the long haul, ocean altimetry is an international commitment."
Washington (UPI) Aug 9, 2017
Hilarie Sorensen intended to do her master's thesis on crystal jellyfish, the half moon-shaped bioluminescent jellies that are ubiquitous off the West Coast. Instead she'll be researching a jelly-like creature she hadn't heard of before May. That was when the University of Oregon marine biology graduate student went on a two-week research cruise from San Francisco to Newport, Ore. "In p ... read more
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