- 行业: Weather
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The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, AMS has a membership of more than 14,000 professionals, ...
A quantity with the dimensions of kinematic viscosity, defined as ''u''<sub>*</sub>''z''<sub>0</sub>, where ''''u''<sub>*</sub> is the friction velocity and ''z''<sub>0</sub> the aerodynamic roughness length. In smooth flow the macroviscosity is of the order of one-tenth the kinematic viscosity. In normal atmospheric flow, which is fully rough, it is of the order of 10<sup>−2</sup> m<sup>2</sup>s<sup>−1</sup>, or about 1000 times the kinematic viscosity. See logarithmic velocity profile.
Industry:Weather
A quasiperiodic oscillation of the near-equatorial troposphere, most noticeable in the zonal wind component in the boundary layer and in the upper troposphere, particularly over the Indian Ocean and the western equatorial Pacific. This phenomenon is named after the codiscoverers. The oscillation can be detected globally in winds near the tropopause. The period of the oscillation varies between about 30 and 50 days, and appears to represent an eastward-propagating disturbance with the structure of a Kelvin wave with a vertical half-wavelength of the depth of the troposphere, but with a phase speed of only about 8 m s<sup>−1</sup>, much less than that of an adiabatic Kelvin wave. The disturbance is accompanied by strong fluctuations of deep convection, easily detectable using satellite observations, and is a major contributor to intraseasonal weather variability in equatorial regions from eastern Africa eastward to the central Pacific.
Industry:Weather
天気の良い日が吹くと、特に、夏にアドリア海; で北西風最も頻繁に西海岸にあり、東地中海の etesians に相当します。それはコルシカ島とサルデーニャの海岸もあります。ミストラルと比較します。
Industry:Weather
A wind, named after the Maloja Pass between the Engadine and Bergall, Switzerland, that blows down the valley of the Upper Engadine by day and either up or down by night. This deviation from the usual nature of mountain and valley winds is attributed to the fact that the stronger daytime valley wind from the south overtops the ridge and continues down the Engadine.
Industry:Weather
A principal cloud type (cloud genus), gray colored and often dark, rendered diffuse by more or less continuously falling rain, snow, sleet, etc. , of the ordinary varieties and not accompanied by lightning, thunder, or hail. In most cases the precipitation reaches the ground, but not necessarily. Nimbostratus is composed of suspended water droplets, sometimes supercooled, and of falling raindrops and/or snow crystals or snowflakes. It occupies a layer of large horizontal and vertical extent. The great density and thickness (usually many thousands of feet) of this cloud prevent observation of the sun; this, plus the absence of small droplets in its lower portion, gives nimbostratus the appearance of dim and uniform lighting from within. It also follows that nimbostratus has no well-defined base, but rather a deep zone of visibility attenuation. Frequently a false base may appear at the level where snow melts into rain. Nimbostratus usually results from the thickening of altostratus to the point where the sun becomes totally indiscernible (Ns altostratomutatus); this point in time usually coincides with the beginning of relatively continuous precipitation. Rarely, it may evolve in like manner from stratocumulus or altocumulus (Ns stratocumulomutatus or Ns altocumulomutatus). Nimbostratus sometimes forms by the spreading of cumulonimbus or cumulus congestus when these clouds produce rainfall (Ns cumulonimbogenitus or Ns cumulogenitus). By definition, nimbostratus is always accompanied by the complementary features praecipitatio or virga. The accessory cloud, pannus, also is a common feature. At first the pannus consists of separate units, but later they may merge into a continuous layer and extend upward into the nimbostratus. Nimbostratus is most easily confused, in identification, with thick masses of altostratus, stratus, or stratocumulus. Altostratus, however, is lighter in color, appears less uniform from below, and does not completely hide the sun. In case of further doubt, a cloud is called nimbostratus if precipitation from it reaches the ground. Stratus also may have precipitation, but only of very small-sized particles. Stratocumulus shows clear relief and a well-defined limit of its base. See cloud classification.
Industry:Weather
