| Section S | S index | 1301-1309 of 1376 terms |
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surface radiation budget—(Also called surface radiation balance or net radiation, which is the preferred term.) The net radiative flux density across a given point on the earth's surface, averaged over a specified time interval. Major components of the surface radiation budget are downward shortwave (direct plus diffuse solar radiation), upward shortwave (reflected), downward longwave (emitted from different levels of the atmosphere), and upward longwave (emitted from the surface). On a global annual average, the radiation budget for the earth's surface is positive, indicating an excess of solar heating over longwave loss, and is approximately 100 watts per square meter. Instantaneous values, however, may be positive or negative, and range through many hundreds of watts per square meter. In the annual global mean, the positive surface radiation budget is assumed to be matched equally by a negative atmospheric radiation budget so that the planet as a whole is in radiative equilibrium.
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surface renewal model—A turbulent exchange model that assumes that fluid near a surface is intermittently replaced by well-mixed fluid from adjacent layers, thereby disrupting the viscous sublayer at the surface itself. Near-surface gradients are assumed to be restored by conduction according to  where T is temperature and κ is thermal diffusivity.
Kraus, E. B., and J. A. Businger, 1994: Atmosphere–Ocean Interaction, Oxford University Press, 138–147.
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surface retention—(Also called surface storage.) The portion of storm rainfall that is intercepted, stored in depressions, or otherwise sufficiently delayed that it fails to reach the basin outlet within the time interval of the storm hydrograph.
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surface roughness—The geometric characteristic of a surface associated with its efficiency as a momentum sink for turbulent flow, due to the generation of drag forces and increased vertical wind shear. In micrometeorology, the surface roughness is usually measured by the roughness length, a length scale that arises as an integration constant in the derivation of the logarithmic wind profile relation. In neutral stability the logarithmic wind profile extrapolates to zero wind velocity at a height equal to the surface roughness length. Several formulas exist to parameterize this length scale as a function of the roughness element geometry (e.g., spacing and silhouette area). Tabulated values for various surface types are published in most micrometeorological texts. See momentum flux, zero-plane displacement.
Stull, R. B., 1988: An Introduction to Boundary Layer Meteorology, 666 pp.
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surface runoff—The water that reaches streams (ranging from the large permanent streams to the tiny rills and rivulets that carry water only during rains) by traveling over the surface of the soil. Thus, surface runoff takes place only over the relatively short distance to the nearest minor channel. See overland flow.
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