| Section S | S index | 1271-1279 of 1376 terms |
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surf beat—A nearshore phenomenon of the long period disturbance in surf zone associated with the occurrence of wave groups. One example is the release and reflection of bounded long waves by breaking wave groups in the surf zone.
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surf—The wave activity occurring on a beach inshore of the point at which incoming waves break. Generally, surf consists of waves that have broken and therefore have air to some degree mixed in with the water.
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surface albedo—The ratio, expressed as a percentage, of the amount of electromagnetic radiation reflected by the earth's surface to the amount incident upon it. Value varies with wavelength and with the surface composition. For example, snow and ice vary from 80% to 85% and bare ground from 10% to 20%. Compare albedo.
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surface-based lifted index—(Abbreviated SBLI.) A stability index that is identical to the lifted index (LI) except that it modifies the standard 1200 and 0000 UTC soundings or numerical-model soundings by incorporating hourly surface observational data, and the characteristics of the lifted parcel are from surface values of temperature and dewpoint. The advantage of this index is that it can be computed at hourly intervals and it typically reflects short-term changes in the boundary layer. The surface-based lifted index is typically more unstable than the LI. As with the LI, thunderstorms become increasingly likely the further the surface- based lifted index decreases below a threshold of zero.
Hales, J. E., Jr., and C. A. Doswell III, 1982: High-resolution diagnosis of instability using hourly surface- lifted parcel temperatures. Preprints, 12th Conf. on Severe Local Storms, 172–175.
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surface chart—(Also called surface map, sea level chart, sea level pressure chart.) An analyzed chart of surface weather observations. Essentially, a surface chart shows the distribution of sea level pressure, including the positions of highs, lows, ridges, and troughs and the location and character of fronts and various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. Often added to this are symbols of occurring weather phenomena, analysis of pressure tendency (isallobars), indications of the movement of pressure systems and fronts, and perhaps others, depending upon the intended use of the chart. Although the pressure is referred to mean sea level, all other elements on this chart are presented as they occur at the surface point of observation. A chart in this general form is the one commonly referred to as the weather map. When the surface chart is used in conjunction with constant-pressure charts of the upper atmosphere (e.g., in differential analysis), sea level pressure is usually converted to the height of the 1000-mb surface. The chart is then usually called the 1000-mb chart.
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Surface Composition Mapping Radiometer—(Abbreviated SCMR.) A three-channel scanning radiometer on Nimbus-5 (launched December 1972) measuring radiation in the visible and infrared spectrum to determine the composition of the earth's surface.
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surface current—The current at the sea surface, which is partly due to the effects of wind and waves. Empirically, it is found that the drift current at the surface is 2.5%–3.0% of the wind speed, and it decreases rapidly in the uppermost meter.
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