- 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 theory of thunderstorm charge separation based upon the suggested occurrence of the Lenard effect in thunderclouds, that is, the separation of electric charge due to the breakup of water drops. This theory, advanced by Sir George C. Simpson (1927), was initially intended to account for a bipolar charge distribution within a thundercloud having the main positive charge center near the base of the cloud and the main negative charge center higher up. Simpson's theory, however, does not explain this phenomenon well because temperatures are below the freezing point in this region of the cloud. Evidence does remain to support a weak positive charge center that lies slightly below the lower main negative charge concentration in many, if not all, thunderclouds where the temperature is above the freezing point. Hence, the breaking-drop theory is best ascribed to this localized secondary positive charge center.
Industry:Weather
A term used to designate a climatic station with a long record of data obtained in a single location with minimal change in the environment of the station. Those stations originally designated benchmark stations are now considered part of the “Historical Climatic Network. ”
Industry:Weather
A term commonly applied to a pair of metallic strips with different thermal expansion coefficients that have been bound together to form a single strip. The purpose is to create a device that converts temperature into a mechanical signal either as a visible temperature reference or as part of a thermal control system (e.g., a thermostat).
Industry:Weather
A technique used by wind profilers to determine the vertical profile of the wind vector above the radar by measuring the line-of-sight component of the wind sequentially along each of several different beam directions. The different beam directions can be obtained in various ways: 1) mechanically steering a single fixed-beam antenna; 2) electronically or mechanically steering the beam of a single fixed-position antenna (see phased-array antenna); or 3) switching between multiple fixed-beam antennas. Three beam positions can be used to determine the wind vector if it is assumed that the wind field is the same along those beams. At least five beam positions must be used to measure both the wind and its divergence. Wind profilers typically use one vertical beam and oblique beams that are between 10° and 25° off vertical. Oblique angles closer to the zenith make separation of horizontal and vertical wind components difficult and larger zenith angles make it less likely that the wind is uniform over the horizontal distances between beams. Large zenith angles also increase the radial range to the scattering volume at a given altitude, thereby reducing the strength of the returned signal.
Industry:Weather
A systematic method of dimensional analysis, whereby variables that are relevant to a particular atmospheric situation are formed into dimensionless groups called Pi groups. Because the number of dimensionless groups equals the original number of variables minus the number of fundamental dimensions present in all the variables, this analysis reduces the degrees of freedom for the physical situation and can be used to guide the design of measurement programs. Buckingham Pi theory is often used in similarity theory to identify the relevant dimensionless groups. Fundamental dimensions are length, mass, time, temperature, electric current, and luminous intensity. All other dimensions can be formed from combinations of these fundamental dimensions. See Pi theorem.
Industry:Weather
A system of electrical currents flowing along the direction of the earth's magnetic field, between the outer regions of the magnetosphere and the ionosphere. Birkeland currents are confined to the auroral zones, and are intimately related to the aurora itself. They are named after Kristian Birkeland, an early Norwegian scientist, who first proposed the existence of such currents.
Industry:Weather
A system of estimating and reporting wind speeds using a numerical scale ranging from 0 (calm) to 12 (hurricane). It was invented in the early nineteenth century by Admiral Beaufort of the British Navy and was originally based on the effects of various wind speeds on the amount of canvas that a full- rigged frigate of the period could carry. It has since been modified and modernized and in its present form for international meteorological use it equates 1) Beaufort force (or Beaufort number), 2) wind speed, 3) descriptive term, and 4) visible effects upon land objects or sea surface. One land adaptation is the NRM wind scale.
Industry:Weather
A strong northeast wind in Russia and central Asia. It is most frequent in winter when it resembles a blizzard, that is, very cold and lifting snow from the ground; as such it is called white buran or, on the tundra, purga. A similar wind in Alaska is called burga. The buran also occurs, but less frequently, in summer, when it raises dust clouds; it is then called karaburan.
Industry:Weather
A synoptic-scale cloud pattern frequently observed in satellite imagery just prior to the onset of cyclogenesis. The cloud system is an elongated pattern with well-defined borders on both sides. It is associated with midtropospheric frontogenesis.
Industry:Weather
A structure, usually rock or concrete, protecting a shore area, harbor, or beach from wave action.
Industry:Weather
