| Section S | S index | 791-799 of 1376 terms |
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speed-up height—The height above hilltop experiencing the greatest increase in wind speed due to the Bernoulli effect, as compared to the upstream value of the wind speed at the same height.
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speed-up ratio—The increase in speed of air that accelerates over the tops of hills due to the Bernoulli effect divided by the ambient wind speed well upwind of the hill.
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speed-up wind—The increase in wind speed above the top of a hill due to the Bernoulli effect.
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sphere calibration—The procedure of calibrating a radar by measuring the power reflected by and returned to the radar from a conducting sphere of a known radar cross section. In principle, this method establishes the radar constant, including the effects of the antenna gain and any attenuation of the signal in the radar system between the antenna and the receiver, effects that are sometimes difficult to estimate by other means. In practice, the method is sometimes difficult to apply. The approach is usually to suspend the sphere beneath a tethered (sometimes free-floating) balloon. The problem is to keep the moving sphere at the center of the radar beam during the time required for a measurement of the returned power.
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spherical albedo—The albedo of a surface when the incident radiation is isotropic. Spherical albedos are also used as the average of the plane albedo over all sun angles, or as the effective albedo of an entire planet.
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spherical coordinates—(Also called polar coordinates in space, geographical coordinates.) A system of curvilinear coordinates in which the position of a point in space is designated by its distance r from the origin or pole along the radius vector, the angle φ between the radius vector and a vertically directed polar axis called the cone angle or colatitude, and the angle θ between the plane of φ and a fixed meridian plane through the polar axis, called the polar angle or longitude. A constant-amplitude radius vector r confines a point to a sphere of radius r about the pole. The angles φ and θ serve to determine the position of the point on the sphere. The relations between the spherical coordinates and the rectangular Cartesian coordinates (x, y, z) are x = r cos θ sin φ; y = r sin θ sin φ; z = r cos φ.
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spherical harmonic—An analytic basis function on the sphere that is commonly used in a spectral model. A spherical harmonic is defined for each total wavenumber n and zonal wavenumber m as the following function of sine of latitude μ and longitude λ:  where Pm,n is the associated Legendre function defined as  The spherical harmonic basis functions satisfy the orthogonal relationship  and they satisfy the elliptic equation on the sphere: 
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spherical harmonics—In analogy to harmonic functions in the plane, the solutions of the Laplace equation in spherical coordinates. Spherical surface harmonics are special sets taken over the surface of a sphere; therefore, the harmonic components are restricted to an integral number of waves over the sphere. Spherical harmonics have been applied in the study of the large-scale oscillations of the atmosphere.
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spherical pyranometer—Radiometer designed to measure only solar radiation incident on the surface of an infinitesimally small sphere. Practically, the sphere of the radiometer is at least 2 cm in diameter.
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spherical pyrgeometer—Radiometer designed to measure only thermal infrared radiation incident on the surface of an infinitesimally small sphere.
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