| Section S | S index | 771-779 of 1376 terms |
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spectral numerical analysisThe expression of a field as a sum of spectral modes. The modes may be Fourier modes or spherical harmonics. While a continuous field can be expressed exactly as a sum of an infinite number of modes, in practice it is approximated as a sum of a finite number of modes with the error confined to the higher unrepresented spectral modes.
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spectral numerical predictionThe forecasting of atmospheric phenomena using a spectral model. The model may be a simple shallow water model or a complex three-dimensional system with full parameterized physics. The model predicts the atmospheric variables in spectral space, but they are generally transformed to physical space for display, dissemination, and verification.
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spectral transform modelA spectral model in which the nonlinear terms in the governing equations are computed in physical space. Thus, for every model time step, some fields must be transformed to physical space where nonlinear terms are computed and then transformed back to spectral space where they can be applied. These nonlinear terms may consist of advection terms, pressure gradient terms, and energy conversion terms, as well as parameterized physics terms. This is the most common kind of spectral model, as it avoids the expensive computation of interactions among modes in spectral space.
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spectrographA spectroscope with a photographic or other recording device to capture an image of the entire spectrum, or portions thereof, at one instant in time.
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spectroheliographAn instrument for taking photographs (spectroheliograms) of an image of the sun in monochromatic light. The wavelength of light chosen for this purpose corresponds to one of the Fraunhofer lines, usually the light of hydrogen and/or ionized calcium. A similar instrument used for visual, instead of photographic, observations is the spectrohelioscope.
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