Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mesoscale ocean eddies impact weather

08.07.2013
Ocean currents have a big impact on weather and climate. Without the Gulf Stream, the climate of Northern and Western Europe would be cooler. Scientists at ETH Zurich now uncovered that also relatively small swirling motions in the ocean, so called eddies, impact weather. A large number of such eddies exists in all oceans at any time, featuring diameters of about one hundred kilometers.

Eddies arise because ocean currents are generally turbulent, affected for instance by the topography of the ocean bottom, explains Ivy Frenger, a postdoc in the group of ETH-professor Nicolas Gruber at the Institute of Biogeochemistry and Pollutant Dynamics.

"An analogy to this topographic effect are the swirls that occur downstream of a rock in a creek", says Frenger. In the ocean, eddies can be carried along by large-scale currents over vast distances, and also move around independently.

Precise satellite measurements

The ETH scientists analysed comprehensive satellite data to determine the impact of these eddies on the overlying atmosphere. Their focus is the Southern hemisphere where such eddies are especially frequent. They detected the eddies based on precise measurements of sea surface topography. "Eddies appear as bumps or dips on the sea surface as the density of water within the eddies differs from that of the surrounding ambient water", explains Frenger.

The scientists investigated data collected over nearly a decade allowing them to extract information for more than 600'000 transient eddies. They compiled these eddy-data, and compared them to the corresponding overlying wind, cloud and precipitation data which had been retrieved by means of satellites as well. The scientists found that so-called anticyclonic (meaning they rotate counter clockwise in the southern hemisphere) eddies cause on average a local increase of near-surface wind speed, cloud cover and rain probability. In contrast, the clockwise rotating (so-called cyclonic) eddies reduce near-surface wind speed, clouds and rainfall.

Increased variability

Surface water in anticyclonic eddies is warmer than in their surroundings, for cyclonic eddies it is the opposite. These temperature differences mainly reflect the origin of the eddies, meaning they originate from either warmer or cooler waters relative to their current position. Frenger and colleagues computed that wind speed increases by roughly 5 percent, cloud cover by 3 percent and rain probability by 8 percent for each degree Celsius that an eddy is warmer than its ambient water.

According to Frenger, the number of warm and cold eddies is similar in most of the ocean, so that their opposite signals in the atmosphere tend to neutralize themselves, likely leading to only a small change on average. However, the oceanic eddies increase atmospheric variability and hence may influence extreme events. If a storm blows over such an eddy, peaks in the wind speed may be diminished or amplified depending on the sense of rotation of the underlying eddy. Possibly, eddies may also influence the intensity or course of such a storm. "It is important to know the variability caused by ocean eddies and account for it in weather and climate models", concludes Frenger. In addition, in areas where either warm or cold eddies dominate, they may also have larger-scale effects.

Indications for the mechanism

This study is the first examining such eddies systematically with regard to their impacts not only on wind and clouds but also on rainfall. Further, the ETH scientists inferred the mechanism of this phenomenon based on the spatial pattern of the local changes of the weather above the eddies. Two main hypotheses have been discussed in the literature: the first argues that the anomalous sea surface temperatures of the eddies cause a change in the overlying temperature of the atmosphere, which in turn results in changes in surface pressure. This leads to a compensating air flow, more specifically wind. If this hypothesis was true, one would expect wind speed changes at the edge of eddies.

However, the data evaluated by the ETH scientists reveal that the wind speed changes not at the edge of eddies, but rather at the centre. This points to another mechanism to be dominant, one where the anomalous ocean surface temperature modifies primarily the level of turbulence in the overlying atmosphere: the warmer the eddy, the greater the disturbance in the atmosphere above and the greater the altitude to which the eddy affects the lower atmosphere, which subsequently may change wind, clouds and rain.

In this project, the scientists so far only examined the impact of ocean eddies on weather, neglecting the possibility that the resulting changes in the atmosphere influence the ocean, leading to a fully coupled atmosphere ocean system at scales of 100 kilometres and less. In an on-going study, the researchers are investigating this effect with computer simulations.

Literature reference

Frenger I, Gruber N, Knutti R, Münnich M: Imprint of Southern Ocean eddies on winds, clouds and rainfall. Nature Geoscience, 2013, Advance Online Publication, doi: 10.38/ngeo1863

Nicolas Gruber | EurekAlert!
Further information:
http://www.env.ethz.ch

More articles from Earth Sciences:

nachricht The melting ice makes the sea around Greenland less saline
16.10.2017 | Aarhus University

nachricht WSU researchers document one of planet's largest volcanic eruptions
12.10.2017 | Washington State University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

Im Focus: New nanomaterial can extract hydrogen fuel from seawater

Hybrid material converts more sunlight and can weather seawater's harsh conditions

It's possible to produce hydrogen to power fuel cells by extracting the gas from seawater, but the electricity required to do it makes the process costly. UCF...

Im Focus: Small collisions make big impact on Mercury's thin atmosphere

Mercury, our smallest planetary neighbor, has very little to call an atmosphere, but it does have a strange weather pattern: morning micro-meteor showers.

Recent modeling along with previously published results from NASA's MESSENGER spacecraft -- short for Mercury Surface, Space Environment, Geochemistry and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Taking screening methods to the next level

17.10.2017 | Life Sciences

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

‘Find the Lady’ in the quantum world

17.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>