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Section T T index 561-569 of 589 terms Previous 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Next turbulent transport—The movement of a substance or characteristic by eddy motions of the wind. See turbulent flux. Turner angle—A parameter used to define the local stability of an inviscid water column to double- diffusive convection. Defined as where tan−1 is the four-quadrant arctangent, α is the coefficient of thermal expansion, β is the coefficient of saline contraction, T is temperature, and S is salinity. If −45° < Tu < 45°, the column is statically stable. If −90° > Tu or Tu > 90°, the column is statically unstable to Rayleigh– Taylor instability. If −90° < Tu < −45°, the column is unstable to diffusive convection. If 45° < Tu < 90°, the column is unstable to salt fingering. turning latitude—The latitude below which the meridional structure of an equatorial gravity or Rossby wave is wavelike and beyond which the meridional structure is decaying. With the β-plane approximation, the turning latitude (one in each hemisphere) is defined as where n is the meridional mode number, c is the phase speed of a given vertical mode Kelvin wave, and β is the derivative of Coriolis parameter f with respect to latitude. turnover frequency—Same as Nyquist frequency. TVS—Abbreviation for tornadic vortex signature. TWERLE—Abbreviation for Tropical Wind Energy Conversion and Reference Level Experiment. twilight arch—Same as bright segment. twilight correction—In the interpretation of the records of sunshine, the difference between the time of sunrise and the time at which a record of sunshine first began to be made by the sunshine recorder; and conversely at sunset. This correction is added only when the horizon is clear during the period. twilight glow—A faint, constant glow seen in the twilight sky and associated with airglow. twilight—The period after sunset or before sunrise when all or part of the sky is visibly bright because of sunlight scattered by clouds or the clear sky. Twilight also refers to the sky's appearance during this period. By convention, there are three sequential stages of twilight: civil twilight, nautical twilight, and astronomical twilight. (Some definitions of twilight set its upper limit as high as sun elevations h0 = 5°–10°.) Regardless of cloud cover, illuminance at the earth's surface decreases steadily during evening twilight and increases during morning twilight. However, under partly cloudy or overcast skies, some minor brightness fluctuations can occur as twilight progresses. The color and luminance patterns of clear skies change in complex ways throughout twilight (see bright segment, dark segment, purple light), while overcast skies usually grow bluer during evening civil twilight. The length of nautical, astronomical, and civil twilight varies greatly with latitude and time of year. The annual range of the duration of twilight increases with latitude. For example, at polar latitudes twilight may last as long as 24 hours or may not occur at all. Compare dawn, dusk.           List, R. J., Ed., 1951: Smithsonian Meteorological Tables, 6th rev. ed., 506–520. Previous 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Next