| Section S | S index | 931-939 of 1376 terms |
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static pressure—In engineering fluid mechanics, the pressure in a homogeneous incompressible fluid in steady flow along a level streamline at points other than the stagnation point. Thus if p is the static pressure, Bernoulli's equation gives  where is the density of the fluid, V the speed, and p1 the pressure at the stagnation point, called the total pressure. The kinetic energy per unit volume (1/2)V2 is also called the dynamic pressure. The static pressure is that measured by a barometer moving with the fluid. Since the static pressure is the pressure in the moving fluid and is distributed along the streamline exactly as the hydrodynamic pressure, the terminology is most unfortunately chosen. Since it is rigorously defined only when Bernoulli's equation applies, meteorologists do well in avoiding the term. The unqualified term “pressure” is quite satisfactory in this connection. However, the instrumental precautions taken in measuring the static pressure in fluid mechanics must also be applied to meteorological barometers so that it is the pressure and not the wind speed that is being measured. The measured meteorological pressure is in approximate hydrostatic equilibrium because of the relatively small vertical accelerations in the atmosphere, but this condition does not ordinarily obtain in those studies in which the concept of static pressure is used. Thus static pressure and hydrostatic pressure must be distinguished.
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static stability—(Also called hydrostatic stability, vertical stability.) The ability of a fluid at rest to become turbulent or laminar due to the effects of buoyancy. A fluid, such as air, tending to become or remain turbulent is said to be statically unstable; one tending to become or remain laminar is statically stable; and one on the borderline between the two (which might remain laminar or turbulent depending on its history) is statically neutral. The concept of static stability can also be applied to air not at rest by considering only the buoyant effects and neglecting all other shear and inertial effects of motion. However, if any of these other dynamic stability effects would indicate that the flow is dynamically unstable, then the flow will become turbulent regardless of the static stability. That is, turbulence has physical priority, when considering all possible measures of flow stability (e.g., the air is turbulent if any one or more of static, dynamic, inertial, barotropic, etc., effects indicates instability). Turbulence that forms in statically unstable air will act to reduce or eliminate the instability that caused it by moving less dense fluid up and more dense fluid down, and by creating a neutrally buoyant mixture. Thus, turbulence will tend to decay with time as static instabilities are eliminated, unless some outside forcing (such as heating of the bottom of a layer of air by contact with the warm ground during a sunny day) continually acts to destabilize the air. This latter mechanism is one of the reasons why the atmospheric boundary layer can be turbulent all day. Compare dynamic stability, lapse rate, Brunt–Väisälä frequency, nonlocal static stability, adiabatic equilibrium; see also slice method, buoyant instability
Stull, R. B., 1991: Static stability—An update. Bull. Amer. Meteor. Soc., 72, 1521–1529.
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static—Audio frequency signals, usually regarded as noise, that are detected by radio receivers. Radio noise emitted by lightning is the most common natural source of static. There are also many common man-made sources, such as corona discharges from high-voltage transmission lines, defective vehicular ignition systems, and high-power switching relays for large motors.
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station continuity chart—A chart or graph on which time is one coordinate and one (or more) of the observed meteorological elements at that station is the other coordinate. Compare continuity chart.
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