ocean currents have a big impact on weather and climate. without the
1 stream, the climate of northern and western europe would be cooler. scientists at eth zurich now uncovered that also
2 small
3 motions in the ocean, so called
4, 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（骚乱的）,
5 for instance by the
topography（地势） of the ocean bottom, explains
6 frenger, a postdoc in the group of eth-professor nicolas gruber at the institute of biogeochemistry and
7 8. "an analogy to this topographic effect are the
9 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
10 of water within the eddies differs from that of the surrounding
ambient（周围的） 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
11-data, and compared them to the corresponding overlying wind, cloud and precipitation data which had been
12 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
13) 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
14 that wind speed increases by roughly 5 percent, cloud cover by 3 percent and rain probability by 8 percent for each degree
15 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
16 themselves, likely leading to only a small change on average. however, the oceanic eddies increase
17 variability and hence may influence extreme events. if a storm blows over such an eddy, peaks in the wind speed may be diminished or
18 depending on the sense of
19 of the
20 eddy. possibly, eddies may also influence the
21 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.
收听单词发音 
