- 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 movement of ocean water characterized by regularity, either of a cyclic nature or, more commonly, as a continuous stream flowing along a definable path. Three general classes, by cause, may be distinguished: 1) currents related to seawater density gradients, comprising the various types of gradient current; 2) wind-driven currents, which are those directly produced by the stress exerted by the wind upon the ocean surface; and 3) currents produced by long-wave motions. The latter are principally tidal currents, but may include currents associated with internal waves, tsunamis, and seiches. The major ocean currents are of continuous, stream-flow character, and are of first-order importance in the maintenance of the earth's thermodynamic balance.
Industry:Weather
The global recirculation of water masses that determines today's climate. The conveyor belt is driven by the sinking of North Atlantic Deep Water (NADW) through cooling of the surface water in the Greenland and Labrador Seas. NADW flows southward through the Atlantic below a depth of 3000 m. When it reaches the Antarctic Circumpolar Current (ACC), some of it continues into the Indian and Pacific Oceans at depth, enters the Atlantic through the Drake Passage and returns to the North Atlantic. Most NADW, however, rises very close to the surface in the ACC, where it freshens considerably through contact with surface water and enters all three oceans as Antarctic Intermediate Water at depths of 700–1000 m. Antarctic Intermediate Water penetrates into the Northern Hemisphere, being slowly entrained by central water, the water mass above it. Pacific central water enters the Indian Ocean through the Indonesian Seas. It then joins Indian central water to flow eastward and then southward in the subtropical gyre. Agulhas Current eddies carry it into the Atlantic, where it moves northward with the Benguela and Brazil Currents and in the Gulf Stream system toward the Greenland and Labrador Seas to cool and sink again, thus completing the conveyor belt circulation.
Industry:Weather
1. In meteorology, the process of formation of an occluded front. Some persons restrict the use of this term to the usual case where the process begins at the apex of a wave cyclone; when the process begins at some distance from the apex, they call it seclusion. 2. Same as occluded front.
Industry:Weather
1. The intercommunicating body of saltwater occupying the depressions of the earth's surface. 2. One of the major primary subdivisions of the above, bounded by continents, the equator, and other imaginary lines. See sea.
Industry:Weather
1. In U. S. Weather observing practice, the designation for the sky cover when the sky is completely hidden by surface-based obscuring phenomena. It is encoded “X” in aviation weather observations; it always constitutes a ceiling, the height of which is the value of vertical visibility into the obscuring phenomenon. Compare partial obscuration. 2. A surface-based obscuring phenomenon.
Industry:Weather
A front that forms as a cyclone moves deeper into colder air. This front will separate air behind the cold front from air ahead of the warm front. This is a common process in the late stages of wave-cyclone development, but is not limited to occurrence within a wave cyclone. There are three basic types of occluded front, determined by the relative coldness of the air behind the original cold front to the air ahead of the warm (or stationary) front. 1) A cold occlusion results when the coldest air is behind the cold front. The cold front undercuts the warm front and, at the earth's surface, coldest air replaces less cold air. 2) When the coldest air lies ahead of the warm front, a warm occlusion is formed, in which case the original cold front is forced aloft at the warm front surface. At the earth's surface, coldest air is replaced by less cold air. 3) A third and frequent type, a neutral occlusion, results when there is no appreciable temperature difference between the cold air masses of the cold and warm fronts. In this case frontal characteristics at the earth's surface consist mainly of a pressure trough, a wind-shift line, and a band of cloudiness and precipitation. See bent-back occlusion.
Industry:Weather
Any cyclone (or low) within which there is little or no temperature advection; typically associated with the formation of an occluded front.
Industry:Weather
In U. S. Weather observing practice, one of a class of atmospheric phenomena, other than the weather class of phenomena, that may reduce horizontal visibility at the earth's surface. Obstructions to vision are listed in the Manual of Surface Observations (WBAN), Circular N, as follows: fog, ground fog, blowing snow, blowing sand, blowing dust, ice fog, haze, smoke, dust and blowing spray. These are encoded as a part of an aviation weather observation.
Industry:Weather
The Doppler velocity signature of middle-altitude flow around the strong updraft region of a severe thunderstorm. The signature indicates stronger flow around the edges of the updraft region and weaker (or reversed) flow in the wake region immediately downwind. Though present for all radar viewing directions, it is most pronounced when a significant component of storm motion is toward or away from the radar.
Industry:Weather
