| Section T | T index | 571-579 of 589 terms |
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twin-gauge station—(Also twin-gage station.) Gauging station at which two water level gauges are used to define the water surface slope for developing a stage–discharge relationship.
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twister—In the United States, a colloquial term for tornado.
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twisting term—(Also called tilting term, tipping term.) The term in the vorticity equation that represents the generation of vertical vorticity by the twisting of horizontal vorticity into the vertical through the agency of shear in the vertical velocity. In symbols this term is  where u, v, and w are the velocity components along the coordinate directions x, y, and z, respectively.
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two-dimensional model—A mathematical model of the atmosphere that simulates variations of concentration with two spatial coordinates (usually vertical and latitudinal) as a function of time. Since the prevailing winds tend to move zonally (around circles of latitude), variations in chemical concentrations tend to be less pronounced in that coordinate, and the simplification resulting from using a zonally averaged model leads to a considerable saving in computation time.
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two-dimensional turbulence—The special case of turbulence in which the scales of the turbulent velocities in two dimensions (often the horizontal plane) are much larger than in the third dimension, and the horizontal eddies can be treated separately from the vertical. In consequence, the equations of geophysical fluid dynamics can be formulated in especially simple and productive forms for applications to atmospheric and oceanic flows. Applications include especially study of large-scale atmospheric and oceanic disturbances, the general circulation, and climate change. See also two-dimensional eddies.
Frisch, U., 1995: Turbulence: The Legacy of A. N. Kolmogorov, Cambridge University Press, 240–241.
Tennekes, H., and J. L. Lumley, 1972: A First Course in Turbulence, MIT Press, p. 91.
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two stream—An approximate technique for handling the complexity of monochromatic radiative transfer in atmospheric models. The technique reduces the directionality of the problem to an upwelling and a downwelling irradiance, and provides moderate accuracy for reflected and transmitted irradiances with little computational expense. Several variations of the two-stream technique exist, suited to different problems.
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