- 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, ...
1. A violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud. When tornadoes do occur without any visible funnel cloud, debris at the surface is usually the indication of the existence of an intense circulation in contact with the ground.
On a local scale, the tornado is the most intense of all atmospheric circulations. Its vortex, typically a few hundred meters in diameter, usually rotates cyclonically (on rare occasions anticyclonically rotating tornadoes have been observed) with wind speeds as low as 18 m s<sup>−1</sup> (40 mph) to wind speeds as high as 135 m s<sup>−1</sup> (300 mph). Wind speeds are sometimes estimated on the basis of wind damage using the Fujita scale. Some tornadoes may also contain secondary vortices (suction vortices). Tornadoes occur on all continents but are most common in the United States, where the average number of reported tornadoes is roughly 1000 per year, with the majority of them on the central plains and in the southeastern states (see Tornado Alley). They can occur throughout the year at any time of day. In the central plains of the United States they are most frequent in spring during the late afternoon. See Also supercell tornado, nonsupercell tornado, gustnado, landspout, waterspout.
2. A violent thundersquall in West Africa and adjacent Atlantic waters.
Industry:Weather
1. A transparent, colorless, odorless, and tasteless liquid found near the surface of the earth. In the lithosphere, hydrosphere, and atmosphere of the earth, water is found as a gas, liquid, and solid. Water falls from the clouds as rain, hail, sleet, graupel, snow, etc. , and runs off and through soils to form creeks, streams, rivers, and lakes. In its solid form, it is referred to as ice or snow. Water as a liquid and as ice covers 70. 8% of the surface of the earth and plays a fundamental part in the earth–atmosphere energy balance. Water (chemical formula ''H''<sub>2</sub>''O'') corresponds to two parts hydrogen and one part oxygen on a molecular basis; by weight, water is 11. 19% hydrogen and 88. 81% oxygen. Water has a melting point of 0°C (32°F), a boiling point of 100°C (212°F), and a specific gravity of 1. 000 at 4°C (39°F), by definition. 2. Can refer to a body of water, such as a lake or a stream, or even a larger body of water such as a sea or part of an ocean, for example, international waters. 3. Used to describe water in specific locales; for example, hydrologists refer to soil water, surface water, and groundwater. 4. As a verb, used to describe irrigation corresponding to the application of water to plants, the grounds surrounding a residence, or to a garden.
Industry:Weather
1. A specific classification of aircraft having the same basic design, including all modifications that result in a change in handling or flight characteristics. 2. See weather type.
Industry:Weather
1. A low dam built across a stream to raise the upstream water level. 2. A structure built across a stream or channel for the purpose of measuring flow.
Industry:Weather
1. A linkage between weather changes occurring in widely separated regions of the globe. 2. A significant positive or negative correlation in the fluctuations of a field at widely separated points. Most commonly applied to variability on monthly and longer timescales, the name refers to the fact that such correlations suggest that information is propagating between the distant points through the atmosphere.
Industry:Weather
1. A relatively heavy coating of hoarfrost. With respect to vegetation, a white frost is less damaging than a black frost for at least two reasons: 1) it tends to insulate the plant from further cold; and 2) it releases latent heat of fusion (albeit slight) to the environment. 2. Colloquial term for a deposit of fine rime.
Industry:Weather
1. A layer that is commonly used as a reference, such as the boundary layer that has a height above the earth's surface of zero. 2. A layer within which some measured quantity is zero, such as the level of nondivergence.
Industry:Weather
1. A height scale in turbulent flow over tall roughness elements associated with the average level of action of momentum transfer between the flow and the roughness elements. In neutral stability the logarithmic wind profile becomes a straight line only if the vertical axis is shifted by the zero-plane displacement length. Several formulas exist to relate this height scale as a function of the roughness element geometry (for example, spacing and silhouette area). Tabulated values for various surface types are published in most micrometeorological texts, for example, Oke (1987). See surface roughness. 2. (Also called displacement distance, displacement thickness. ) In a viscous homogeneous fluid, the depth of a boundary layer of shearing flow over a flat plate.
Industry:Weather
1. A chemical or thermodynamic property of the flow that is conserved during advection. It can be used to track air-parcel movement and to identify the origins of air masses. Examples are absolute humidity, equivalent potential temperature, radioactivity, and CCN composition. 2. Any substance in the atmosphere that can be used to track the history of an air mass. It can be chemical or radioactive in nature. The main requirement for a tracer is that its lifetime be substantially longer than the transport process under study. An example of an inert chemical tracer is SF<sub>6</sub>, which is often released during a field experiment and measured at a later time to assess the extent of dilution of the air mass. Chemicals such as methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O), which are released at the earth's surface and destroyed slowly in the atmosphere, can be used to infer vertical rates of transport. CO released in the boundary layer can be used to trace transport in convection. Radioactive tracers such as <sup>14</sup>C and <sup>90</sup>Sr have been used to test models of stratospheric circulation. Certain atmospheric gases have also been used as tracers in ocean waters, for example, the chlorofluorocarbons.
Industry:Weather
1. A band in the electromagnetic spectrum that offers maximum transmission and minimal attenuation through a particular medium with the use of a specific sensor. See atmospheric window. 2. Open water in a predominantly frozen river. It is caused by warmer water from a spring or tributary, or by turbulence over a shoal. See polyn'ya. 3. (Obsolete. ) A term for the chaff used for military countermeasure purposes during World War II.
Industry:Weather
