ESA GOCE: Monitoring Ocean currents

The ocean currents and their speeds (in cm/s) derived from ESA's GOCE data. 

During the mission’s final year, its super-low orbit was lowered even further to obtain improved measurements of Earth’s gravity field, from which information on ocean currents was derived. 

Buoys floating in the oceans were used to validate the above map, proving that this GOCE-based model is more accurate than any other model based on space-based data to date. 

Credit: ESA

The mean dynamic topography (MDT, in cm) of the world’s oceans in the highest resolution ever achieved from space-based data. 

MDT is calculated by taking the mean sea-surface height measured by satellites like Envisat, and subtracting the gravity model from GOCE. 

Red areas show where water levels are above the surface of the gravity model, while blue depicts areas where the water is below. From this, scientists calculated the speed of ocean currents.

A year after the satellite reentered the atmosphere, scientists using data from the GOCE satellite have made a breakthrough in our understanding of ocean currents.

The Gravity field and steady-state Ocean Circulation Explorer (GOCE), mapped variations in Earth’s gravity with unrivalled precision, resulting in the most accurate shape of the ‘geoid’ – a hypothetical global ocean at rest – ever produced.

While the mission is well known for its gravity measurements, the second mission objective as an ‘ocean circulation explorer’ has reached a milestone.

Using GOCE data, scientists have produced the most accurate model of ocean current speeds to date.

To do this, the GOCE geoid was subtracted from the mean sea-surface height measured over a 20-year period by satellites including ESA’s veteran Envisat.

In 2011, GOCE delivered a model of the 'geoid' pictured here. At the time, it was the most accurate ever produced. 

The colours in the image represent deviations in height (–100 m to +100 m) from an ideal geoid. 

The blue shades represent low values and the reds/yellows represent high values. 

Credit: ESA

The result shows the mean dynamic topography of the ocean surface, showing higher- and lower-than-average water levels. Based on this map, ocean currents and their speeds were calculated and validated using in situ buoys.

The result shows that this GOCE-based model is more accurate than any other model based on space data to date.

“The accurate estimate of ocean surface currents, as provided today by the combination of GOCE and altimetry data, is crucial for the better understanding of the ocean dynamics,” said Marie-Hélène Rio from the Institute of Atmospheric Sciences and Climate of the Italian National Research Council.

“In particular, the assimilation of this information into operational ocean monitoring and forecasting systems will provide highly valuable new insight into the present and future state of the ocean.”

This was just one of many GOCE results presented today at the opening of the 5th International GOCE User Workshop at the UNESCO Headquarters in Paris, France.

Galileo: Ocean Currents Shaping Europa's Icy Shell, Critical for Potential Habitats

Zonal flows in Europa-like ocean simulation. 

Image credit: University of Texas Institute for Geophysics.

In a finding of relevance to the search for life in our solar system, researchers at the University of Texas at Austin's Institute for Geophysics, the Georgia Institute of Technology, and the Max Planck Institute for Solar System Research have shown that the subsurface ocean on Jupiter's moon Europa may have deep currents and circulation patterns with heat and energy transfers capable of sustaining biological life.

Scientists believe Europa is one of the planetary bodies in our solar system most likely to have conditions that could sustain life, an idea reinforced by magnetometer readings from the Galileo spacecraft detecting signs of a salty, global ocean below the moon's icy shell.

Without direct measurements of the ocean, scientists have to rely on magnetometer data and observations of the moon's icy surface to account for oceanic conditions below the ice.

Regions of disrupted ice on the surface, known as chaos terrains, are one of Europa's most prominent features.

As lead author Krista Soderlund and colleagues explain in this week's online edition of the journal Nature Geosciences, the chaos terrains, which are concentrated in Europa's equatorial region, could result from convection in Europa's ice shell, accelerated by heat from the ocean.

The heat transfer and possible marine ice formation may be helping form diapirs, or warm compositionally buoyant plumes of ice that rise through the shell.

In a numerical model of Europa's ocean circulation, the researchers found that warm rising ocean currents near the equator and subsiding currents in latitudes closer to the poles could account for the location of chaos terrains and other features of Europa's surface.

Such a pattern coupled with regionally more vigorous turbulence intensifies heat transfer near the equator, which could help initiate upwelling ice pulses that create features such as the chaos terrains.

"The processes we are modeling on Europa remind us of processes on Earth," says Soderlund, where a similar process has been observed in the patterns creating marine ice in parts of Antarctica.

The current patterns modeled for Europa contrast with the patterns observed on Jupiter and Saturn, where bands of storms form because of the way their atmospheres rotate.

The physics of Europa's ocean appear to have more in common with the oceans of the "ice giants" Uranus and Neptune, which show signs of three-dimensional convection.

"This tells us foundational aspects of ocean physics," notes co-author Britney Schmidt, assistant professor at the Georgia Institute of Technology."

"More importantly, adds Schmidt, if the study's hypothesis is correct, it shows that Europa's oceans are very important as a controlling influence on the surface ice shell, offering proof of the concept that ice-ocean interactions are important to Europa.

"That means more evidence that the ocean is there, that it's active, and there are interesting interactions between the ocean and ice shell," says Schmidt, "all of which makes us think about the possibility of life on Europa."

Soderlund, who has studied icy satellites throughout her science career, looks forward to the chance to test her hypothesis through future missions to the Jovian system.

The European Space Agency's JUICE mission (JUpiter ICy moons Explorer) will give a tantalizing glimpse into the characteristics of the ocean and ice shell through two flyby observations.

NASA's Europa Clipper mission concept, under study, would complement the view with global measurements.

Soderlund says she appreciates the chance "to make a prediction about Europa's subsurface currents that we might know the answer to in our lifetimes - that's pretty exciting."

ESA GOCE: Gravity mapper surfs Earth's upper atmosphere

Europe's ultra-low-flying gravity-mapping satellite, Goce, is being manoeuvred even closer to the planet.

The arrow-shaped spacecraft has spent most of its mission at an altitude of 255km - that's about 500km below most other Earth-observing missions.

Engineers are now bringing it down by 20km to improve its data resolution.

But it will be a tricky operation. Goce will have to fight atmospheric drag to stay aloft and maintain the stability needed to measure Earth's gravity.

"The science benefit that you get from decreasing the altitude and thereby increasing the spatial resolution of the data, and also the precision of what you can measure, is quite spectacular," explained mission manager Dr Rune Floberghagen. (Interviewed here)

"We will get about a 35% increase in the quality of the data," he reported.

GOCE: The Gravity Field and Steady-State Ocean Circulation Explorer was launched in 2009.

It is part of a series of innovative research satellites developed by the European Space Agency (Esa).

It carries super-sensitive instrumentation to detect the tiny variations in the pull of gravity across the surface of the planet.

The maps it produces can have very broad applications. The data is a key reference in civil engineering for relating heights measured at widely separated locations, and for the computer models that need to understand how the oceans move to forecast future changes in climate.

Recent successes include producing the first global high-resolution map of the boundary between the rocks of the Earth's crust and its mantle - the famous Mohorovicic (or "Moho") discontinuity, which lies tens of kilometres below the planet's surface.

Nasa: Gulf Stream around North America

This NASA image shows the Gulf Stream around North America.

It is taken from Perpetual Ocean, a visualisation of some of the world's surface ocean currents from June 2005 through December 2007.

Picture: NASA/Reuters

ESA CryoSat breaks the ice with ocean currents

Click on the image to visit ESA Portal and view the animation.

Animation of the intensity of ocean surface currents as predicted by MyOcean’s global ocean model (1/12°) after assimilation of altimetry data. 

In addition to major currents such as the Gulf Stream, the turbulence driving the ocean circulation is visible. 

The blue-to-white colour scale represents surface currents in metres per second.

Credits: MyOcean/Mercator-Ocean

Ocean measurements from ESA’s CryoSat mission are being exploited by the French space agency CNES to provide global ocean observation products in near-real time. Understanding sea-surface currents is important for marine industries and protecting ocean environments.

As it orbits from pole to pole, CryoSat’s main objective is to measure the thickness of polar sea ice and monitor changes in the ice sheets that blanket Greenland and Antarctica. But the satellite also features an innovative radar altimeter that not only detects tiny variations in the height of the ice, but can also measure sea level and the height of the waves.

Starting today , CryoSat ocean measurements are being processed by CNES and distributed to the oceanography community. These products will be assimilated using models from the MyOcean project in near-real time to enhance sea surface products and to improve the quality of the model forecasts.

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Record-breaking current found deep in Southern Ocean

Record-breaking current found deep in Southern Ocean

MORE than 3 kilometres down in part of the freezing Southern Ocean, water is flowing at more than 700 metres per hour, making this the fastest-moving deep ocean current ever found.

The powerful current was discovered thanks to a 175-kilometre string of sensors on the eastern flank of the submerged Kerguelen plateau, some 3000 kilometres south-west of Australia (Nature Geoscience, DOI: 10.1038/ngeo842).

With a flow of more than 8 million cubic metres per second, the current transports 40 times as much water as the Amazon. It is likely to be an important component of the global ocean "conveyor belt", which pushes water from the ocean surface to its greatest depths and back again, and has a direct influence on global temperatures.

Deep ocean currents are now being monitored for signs of change. The measurements already suggest that deep Antarctic waters are warming and becoming less buoyant, perhaps because of climate change.

Jellyfish; The Spoons of the Sea

When to the new eyes of thee
All things by immortal power,
Near or far,
Hiddenly
To each other linked are,
So that thou canst not stir a flower
Without troubling a star...........

(Francis Thompson)

NEXT time you go for a dip in the sea, bear in mind that your deft front crawl is helping to mix up the waters. In fact, marine life may be stirring the oceans and moving nutrients around as much as winds or tides.

According to a theory proposed by Darwin's grandson, Charles Galton Darwin, a body moving through water drags some of the fluid with it.

Darwin's Drift

In "Darwin drift", a high-pressure zone forms at the front of each swimming animal, leaving an area of lower pressure behind, which draws in adjacent water. This results in a net movement of fluid in the direction of the swimmer.

Swarms of Jellyfish

To test the idea, Kakani Katija and John Dabiri at the California Institute of Technology in Pasadena went to a lake in the Republic of Palau in the Pacific Ocean. Diving among swarms of jellyfish, the pair used suspended dyes and a newly designed laser velocimeter to measure the movement of water around the jellyfish. They found that the animals did indeed drag water with them as they swam (Nature, vol 460, p 624).

Mixing Energy

The researchers then estimated the total energy that all ocean swimmers impart on the water. They calculated that it was on a par with the mixing energy imparted by winds or tides. The findings suggest ocean swimmers can move water over long distances and that they could help run the vertical currents that push nutrients around between the sea floor and surface waters.