| Section S | S index | 1321-1329 of 1376 terms |
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surface wind stressThe force per unit area on a surface due to the airflow above it. For a mean wind speed Ur at a reference height zr, drag coefficient CD(zr) for that same reference height, and air density , the surface wind stress τ is given by τ = CD(zr)Ur2.
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surfactant filmA thin film on the water surface, usually due to long-chain molecules with one hydrophilic end and one hydrophobic end. Such a film has a surface tension that varies with the surfactant concentration, and the resulting effect on the near-surface viscous boundary layer causes considerably enhanced damping of centimeter-scale waves.
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surge currentA short-duration, high-amperage, electric current impulse that may sweep through an electrical network, as a power transmission network, when some portion of it is strongly influenced by the electrical activity of a thunderstorm. This activity may take the form of a direct lightning strike, or it may be simply the release of previously induced charge on the line when a thundercloud overhead suddenly discharges itself. Such current surges flow rapidly through the lines until they find a path to the ground through arc-over at a weak insulator or by entering terminal equipment at the end of the line. Use of grounded guard wires above the power lines of a transmission system reduces the frequency of surge current difficulties, and installation of lightning arresters at sensitive terminal equipment protects the system against damage there.
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surge lineIn meteorology, a line along which a discontinuity in the wind speed occurs. Usually, but not always, the wind speed is strongest upstream from the surge line. Sometimes it is also accompanied by a change in wind direction.
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suroetA persistent, rain-bearing, southwest (sud-ouest) wind on the west coast of France.
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