| Section S | S index | 701-709 of 1376 terms |
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source—In hydrodynamics, a point, line, or area at which mass or energy is added to a system, either instantaneously or continuously. Conversely, a sink is a point where mass or energy is removed from the system. An incompressible fluid will possess sources or sinks of mass only at points where the divergence of its velocity vector is nonzero; a source is associated with positive divergence and a sink with negative divergence (convergence). The fluid is usually assumed to pass outward from a source or inward to a sink equally in all directions along radial lines. The strength of a source, for example, the rate of mass flow of fluid of unit density across a curve enclosing the source, is given by  where r is the distance from the source and vn the radial speed.
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South Atlantic Current—The eastward current that forms the southern part of the South Atlantic subtropical gyre. It is fed by the Brazil Current and follows the subtropical front, gradually losing water to the subtropical gyre and Brazil Current recirculation. About 20–25 Sv (20–25 × 106 m3s−1) reach the African coast and continue as the Benguela Current. Cooling of the warm Brazil Current water along its path makes the South Atlantic Current a heat source for the atmosphere.
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South Equatorial Countercurrent—(Abbreviated SECC.) A band of weak eastward flow in the Atlantic and Pacific Oceans embedded in the South Equatorial Current near 8°S, caused by a wind stress minimum in the Southern Hemisphere trade winds. In the Pacific Ocean the SECC is controlled by the Asian–Australian monsoon and is strongest during the northwest monsoon (December–April), with speeds approaching 0.3 m s−1; it is barely seen during the remainder of the year. East of the date line it decreases rapidly in strength and is absent from the eastern Pacific during most of the year. In the Atlantic Ocean it is weak, narrow, and variable and has its largest speed of little more than 0.1 m s−1 often below the surface at a depth of 100 m.
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South Equatorial Current—(Abbreviated SEC.) The broad region of uniform westward flow driven by the trade winds that forms the northern part of the Southern Hemisphere subtropical gyres. Being directly wind driven, the SEC responds quickly to variations in the wind field and is therefore strongest in winter (August). In the Atlantic Ocean it is found between 3°N and 25°S with speeds of 0.1–0.3 m s−1. In the Pacific Ocean it covers the same latitude band but attains 0.6 m s−1 and a transport of about 27 Sv (27 × 106 m3s−1) in August; this decreases to 7 Sv in February. In the Indian Ocean it occupies the latitude band 8°–30°S during the northeast monsoon (December–April) and expands northward to 6°S in September during the southwest monsoon, with speeds close to 0.3 m s−1 throughout the year.
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south foehn—A foehn wind blowing from south (northern Italy) to north (Switzerland, southern Germany, and western Austria) over the Alps. Because these winds blow from a warmer region to a cooler region, they are often accompanied by dramatic temperature and wind speed increases. The south foehn often results from flow in the warm sector of a cyclone system and thus it often occurs ahead of a cold front.
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South Indian Ocean Current—The eastward current that forms the southern part of the subtropical gyre in the Indian Ocean. It is fed by the Agulhas Current and follows the subtropical front, gradually losing water to the subtropical gyre and Agulhas Current recirculation. East of Africa it begins with 60 Sv (60 × 106 m3s−1) and arrives off the coast of western Australia with 10 Sv, which continues as the West Australian Current. Cooling of the warm Agulhas Current water along its path makes the South Indian Ocean Current a heat source for the atmosphere.
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South Java Current—A seasonal current along the south coast of Java. The current flows southeastward during December–April and northwestward during June– October, when it is associated with coastal upwelling.
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South Pacific convergence zone—(Abbreviated SPCZ.) A persistent and greatly elongated zone of low-level convergence extending from approximately 140°E near the equator to approximately 120°W at 30°S. The zone is not quite linear, but is oriented more west to east near the equator and has a more diagonal orientation (northwest to southeast) at higher latitudes. The low-level convergence of moisture leads to a persistent cloud band along the SPCZ.
Trenberth, K. E., 1991: Teleconnections Linking Worldwide Climate Anomalies, H. Glantz, R. Katz, and N. Nichols, Eds., 22–23.
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