- 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 period of 24 hours in which 0. 01 in. (0. 2 mm) or more of rain is recorded.
Industry:Weather
Sometimes the ratio of the amplitude of the transmitted electric field to the amplitude of the field incident at the optically smooth planar interface between two optically homogeneous media. The incident and transmitted fields are plane harmonic waves and the interface is large in lateral extent compared with the wavelength of the illumination. May also be the ratio of transmitted to incident irradiances, that is, the ratio of the normal (to the interface) component of the transmitted Poynting vector to that of the incident Poynting vector. A better term for this quantity is transmissivity. The transmission coefficient (and hence transmissivity) depends on the angle of incidence of the illumination, its wavelength (by way of the wavelength-dependence of the relative refractive index of the two media), and its state of polarization (See Also reflection coefficient). These coefficients taken together are sometimes called the “Fresnel formulae” or “Fresnel relations. ” Transmission coefficient may mean the ratio of any transmitted to incident irradiance (transmissivity). Transmission coefficient, transmissivity, transmittance, and transmission function are used more or less synonymously but not always consistently. Within the same work two or more of these terms may mean the same physical quantity. Context is a guide to the exact meaning of different authors in different fields and on different occasions, but is not always sufficient to decipher them. Moreover, these terms are not restricted to electromagnetic waves but may be applied to transmission of acoustic and other waves.
Industry:Weather
In meteorology, the flow of air along a latitude circle; more specifically, the latitudinal (east or west) component of existing flow. Compare meridional flow; see zonal index.
Industry:Weather
A short straight line terminating with an arrowhead centered on a station location on a synoptic chart. It represents the direction from which the wind blows. The length of the line may be representative of the wind speed.
Industry:Weather
The position of the sun during the course of a year as it appears to move through successive star groups or constellations; that is, the band of the celestial sphere, 16° in width, through which the ecliptic runs centrally. At all times this band of the heavens contains the sun, the moon, and the principal planets except Venus and Pluto. Ancient astrologers divided the zodiac into twelve equal divisions, each 30° long, and named them for the chief constellations found in each division, the twelve constellations of the zodiac. These constellations were thought by the ancient Greeks (and others) to represent characters in their mythology and were identified with them.
Industry:Weather
A short straight line terminating with an arrowhead centered on a station location on a synoptic chart. It represents the direction from which the wind blows. The length of the line may be representative of the wind speed.
Industry:Weather
In general, a series of generalized synoptic situations or patterns, usually presented in chart form. Weather types are selected to represent typical pressure and frontal patterns and were originally devised as a method for lengthening the effective time-range of forecasts. Similar idealized patterns of upper-air circulation are sometimes referred to as circulation types.
Industry:Weather
A radar that is used to measure vertical profiles of the wind. In general the term is applied to Doppler radars operating in the VHF–UHF band (30 MHz– 3 GHz) that determine the wind by measuring the line-of-sight Doppler shift of scattered signals (Bragg scattering) from refractive index fluctuations caused by turbulence (see clear-air echo). The turbulent scattering structures are assumed to be moving with the same average velocity as the wind. The three-dimensional wind vector is determined by using the beam swinging technique of pointing the radar beam in at least three different directions. Another type of wind profiler radar that operates in the VHF–UHF band uses a technique called spaced antenna drift (SAD). SAD radars use a single vertical-beam transmitting antenna and three or more horizontally spaced, vertical-beam receiving antennas. The horizontal wind is determined from the cross correlation of the received echoes and the vertical wind is determined from the Doppler shift of the echoes. In addition to measuring the wind vector, wind profiler radars can also determine several other atmospheric quantities from the power, mean Doppler shift, and Doppler spectral width of the returned signal. These quantities include the strength of turbulence (parameterized by the refractive index structure constant ''C<sub>n</sub>''<sup>2</sup>), the eddy dissipation rate, atmospheric stability, momentum flux, virtual temperature and heat flux (using the RASS technique), and precipitation rates and drop- size distributions (from scatter from hydrometeors). Doppler lidars and acoustic sounders (sodars) can also be used as wind profilers. The scatterers for lidars are aerosols (for wavelengths around 10 μm) and molecules (for wavelengths less than 1 μm). Acoustic refractive index fluctuations caused by turbulence provide the scattering mechanism for sodars. See Also MST radar, boundary layer radar.
Industry:Weather
In general, a series of generalized synoptic situations or patterns, usually presented in chart form. Weather types are selected to represent typical pressure and frontal patterns and were originally devised as a method for lengthening the effective time-range of forecasts. Similar idealized patterns of upper-air circulation are sometimes referred to as circulation types.
Industry:Weather
In general, any effort to alter artificially the natural phenomena of the atmosphere. The term usually refers to cloud seeding activities, but can also include constructing windbreaks, dissipating fog by the forceful addition of heat or water spray, or preventing frost formation on crops by cloud spray, heating, or mixing processes. Inadvertent weather modification refers to accidental weather effects resulting from the release of greenhouse gases, aerosols, and dust, or changes in albedo or surface properties of the earth associated with urban, industrial, or agricultural activity.
Industry:Weather
