- 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 radioactive gas, atomic number 86, atomic weight 220; an inert gaseous element with radioactive decay, accompanied by emission of alpha particles, responsible for a portion of the ionization observed in the lower atmosphere. It is a member of the thorium family of radioactive elements and is the immediate descendant of the radium isotope of atomic number 88 and atomic weight 224 (called thorium X at one time), which decays by alpha emission to thoron in a half-life of 3. 6 days. Thoron, in turn, decays by alpha emission in a half-life of only 54. 5 seconds, yielding an isotope of polonium. Thoron, like each of the other two radioactive gases (radon and actinon) that are its isotopes, enters the atmosphere by the process of exhalation after its formation by radioactive disintegration within soil or rocks. The very short half-life of thoron allows it little time to be carried from the earth's surface to higher levels, so its contribution to atmospheric ionization is made largely in the lowest few meters of the atmosphere.
Industry:Weather
The situation in which the vertical wind shear vector does not change direction with height. Presented on a hodograph, unidirectional shear appears as a straight line. Unidirectional vertical wind shear does not always indicate unidirectional winds, since a straight-line hodograph can result from many different wind profiles.
Industry:Weather
A local, often abrupt lowering from a cumulonimbus cloud base into a low-hanging accessory cloud, normally a kilometer or more in diameter. A wall cloud marks the lower portion of a very strong updraft, usually associated with a supercell or severe multicell storm. It typically develops near the precipitation region of the cumulonimbus. Wall clouds that exhibit significant rotation and vertical motions often precede tornado formation by a few minutes to an hour.
Industry:Weather
A local, often abrupt lowering from a cumulonimbus cloud base into a low-hanging accessory cloud, normally a kilometer or more in diameter. A wall cloud marks the lower portion of a very strong updraft, usually associated with a supercell or severe multicell storm. It typically develops near the precipitation region of the cumulonimbus. Wall clouds that exhibit significant rotation and vertical motions often precede tornado formation by a few minutes to an hour.
Industry:Weather
The decrease in the lapse rate of temperature encountered at the level of the tropopause.
Industry:Weather
The decrease in the lapse rate of temperature encountered at the level of the tropopause.
Industry:Weather
In general, a local storm, invariably produced by a cumulonimbus cloud and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail. It is usually of short duration, seldom over two hours for any one storm. A thunderstorm is a consequence of atmospheric instability and constitutes, loosely, an overturning of air layers in order to achieve a more stable density stratification. A strong convective updraft is a distinguishing feature of this storm in its early phases. A strong downdraft in a column of precipitation marks its dissipating stages. Thunderstorms often build to altitudes of 40 000–50 000 ft in midlatitudes and to even greater heights in the Tropics; only the great stability of the lower stratosphere limits their upward growth. A unique quality of thunderstorms is their striking electrical activity. The study of thunderstorm electricity includes not only lightning phenomena per se but all of the complexities of thunderstorm charge separation and all charge distribution within the realm of thunderstorm influence. In U. S. Weather observing procedure, a thunderstorm is reported whenever thunder is heard at the station; it is reported on regularly scheduled observations if thunder is heard within 15 minutes preceding the observation. Thunderstorms are reported as light, medium, or heavy according to 1) the nature of the lightning and thunder; 2) the type and intensity of the precipitation, if any; 3) the speed and gustiness of the wind; 4) the appearance of the clouds; and 5) the effect upon surface temperature. From the viewpoint of the synoptic meteorologist, thunderstorms may be classified by the nature of the overall weather situation, such as airmass thunderstorm, frontal thunderstorm, and squall-line thunderstorm.
Industry:Weather
A region in the atmosphere where isotherms or thickness lines are closely packed; therefore, a region of very strong thermal wind.
Industry:Weather
A device that renders visible the paths of high energy subatomic particles. A supersaturated vapor condition is created in a chamber filled with dust-free air by a sudden adiabatic expansion and cooling. In this environment, the small ions formed along the path of a high energy particle act as effective condensation nuclei. The line of droplets so formed can be used to mark the path. See meteorological cloud chamber.
Industry:Weather
Newly deposited snow that is very fluffy and unstable. In general, it falls only during a dead calm at very low air temperatures and will usually have a low liquid to snow depth ratio. See sand snow.
Industry:Weather
