- 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 bank of orographic stratiform crest cloud occurring over a mountain barrier during foehn conditions; same as foehn wall.
Industry:Weather
2 February; in American folklore, a day that is popularly supposed to provide the key to the weather for the remainder of the winter. Specifically, if the groundhog (woodchuck, Marmota monax), upon emerging from its hole, casts a shadow, it will return underground, thereby foreboding more wintry weather. There is no convincing statistical evidence to support this belief. This date, 2 February, is actually Candlemas Day, which is associated with similar beliefs in Europe, but in the United States, the popularity of this legend has come to overshadow the original significance of the day. One of the most popular Groundhog Day celebrations occurs in Punxsutawney, Pennsylvania, when the media gather at sunrise to see whether the local groundhog (named Phil) casts a shadow. See control day.
Industry:Weather
1. Water overflowing the bankfull stage of a natural or artificial waterway. 2. Accumulation of water caused by surface runoff in low-lying areas not usually submerged.
Industry:Weather
1. The rate of recurrence of any periodic phenomenon, often associated with waves of all kinds. Without qualification frequency often means temporal frequency, the rate of recurrence of a time-varying function, but could mean spatial frequency, the rate of recurrence of a space-varying function. Spatial frequency is the reciprocal of the repeat distance (sometimes the wavelength). The dimensions of (temporal) frequency are inverse time. A common unit for frequency is cycle per second, formerly abbreviated cps, but superseded by hertz, abbreviated as Hz. The symbol ν is often used for frequency but f is common in engineering. Period is inverse frequency. Related to frequency, and applied especially to sinusoidally varying quantities, is angular or circular frequency, often denoted by ω = 2πν, with units radians per unit time (e.g., radians per second). 2. In statistics, the number of times a specified event occurs in a given series of observations; for example, the number of rainy days observed at a particular station during a certain period of time. In many types of studies (hydrometeorological, especially) the reciprocal of frequency, the recurrence interval, is used.
Industry:Weather
The rate at which any physical quantity is transported (usually in a hemisphere of directions) across a unit area. The term “flux” indicates flow (rate of transport), and “density” here is an areal (as opposed to volumetric) density. Flux densities often may be written in the form pnv, where n is the number density (volumetric) of carriers of a property p (e.g., mass, charge, momentum, energy) and v is their speed.
Industry:Weather
1. The phase transition of a substance passing from the liquid to the solid state; solidification; the opposite of fusion. In meteorology, this almost invariably applies to the freezing of water. The phase change from the gaseous to the solid state is deposition. Like condensation, the freezing of water involves the process of nucleation. See ice point, freezing point, true freezing point, melting point. 2. Said of an environment when its temperature is equal to or less than 0°C (32°F). See freeze.
Industry:Weather
1. The molecular (viscous) retarding force on an object, such as air, as it moves across the earth's surface. In the atmospheric boundary layer, turbulent drag dominates by many orders of magnitude over molecular frictional drag. 2. The retarding force that an object such as a raindrop or airplane encounters as it moves through the atmosphere.
Industry:Weather
1. The initial formation of a front or frontal zone. 2. In general, an increase in the horizontal gradient of an airmass property, principally density, and the development of the accompanying features of the wind field that typify a front.
Industry:Weather
1. The fuzzy layer of ice crystals on a cold object, such as a window or bridge, that forms by direct deposition of water vapor to solid ice. 2. The condition that exists when the temperature of the earth's surface and earthbound objects fall below freezing. Depending upon the actual values of ambient-air temperature, dewpoint, and the temperature attained by surface objects, frost may occur in a variety of forms. These include a general freeze, hoarfrost (or white frost), and dry freeze (or black frost). If a frost period is sufficiently severe to end the growing season (or delay its beginning), it is commonly referred to as a killing frost. See frost day, ground frost. 3. See frozen ground. 4. Same as hoarfrost. Compare rime.
Industry:Weather
1. The distance upstream of a measurement site, receptor site, or region of meteorological interest, that is relatively uniform. If a measurement site is located in the middle of a farm field with homogeneous land use, and if there are no changes to the land use and no obstructions such as trees or buildings immediately upstream of the site, then the site is said to have “large fetch”. Large fetch is usually considered good if the measurements are to be representative of the atmosphere over the farm field. Similarly, measurements over a homogeneous forest could also have large fetch if there are no clearcuts or changes in the tree characteristics upstream of the measurement site. 2. (Also called generating area. ) An ocean area where waves are generated by a wind having a constant direction and speed. 3. The length of the fetch area, measured in the direction of the wind in which ocean waves are generated. In many cases, the fetch is limited by the upwind distance to the coast.
Industry:Weather
