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 Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>