- 行业: Weather
- Number of terms: 60695
- Number of blossaries: 0
- Company Profile:
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, ...
An equivalent blackbody temperature that characterizes the noise power at the terminals of an antenna. Specifically, the antenna temperature is the temperature of a blackbody radiator that, when placed around an idealized loss-free antenna, produces the same noise power as that of the actual antenna. Antenna temperature may also refer to the noise temperature of the antenna as determined by not only the coupling of the antenna to environmental noise sources, but also noise generated by resistive losses within the antenna.
Industry:Weather
A graphical representation of the radiating properties of an antenna as a function of space coordinates. Typically, the antenna pattern is a diagram showing the radiant intensity, the electric field strength, or the radiant power density emitted from an antenna as a function of the direction from the antenna, in the far-field region unless specified otherwise. The direction of maximum intensity defines the main lobe of the antenna pattern. Other local maxima, weaker than the main lobe, define the secondary lobes or sidelobes of the antenna. In the main lobe, the angular separation in a given plane between the directions at which the intensity falls to one-half its maximum value defines the half-power or 3-dB beamwidth in the plane. The directional sensitivity of an antenna to incoming signals is described by a function identical to the antenna pattern for transmission. Antenna patterns are also used to depict properties of the emitted electromagnetic field other than intensity, for example, the polarization as a function of position in the main lobe. See lobe.
Industry:Weather
For a particular radar system, the smallest measurable value of the depolarization ratio, a limitation imposed by imperfections in the antenna.
Industry:Weather
A measure of the effectiveness of a directional antenna in a given direction compared with a standard reference, usually an isotropic antenna. Specifically, the antenna gain is the ratio of the intensity radiated in a given direction from the antenna to the intensity of an isotropic source emitting the same power as the real antenna. Sometimes the term antenna gain is used in place of axial gain, which is the value of the antenna gain in the direction of the axis of the main lobe. See antenna pattern.
Industry:Weather
The mechanism that illuminates the reflecting surface of an antenna or that distributes the input power to the radiating elements of an array antenna.
Industry:Weather
A conductor or system of conductors for radiating and/or receiving radio energy. As used in radar, the antenna is usually “directional,” that is, it has the property of radiating or receiving radio waves in larger proportion in a given direction than in others. It includes both the basic radiating element or feed (such as dipole antenna or horn antenna) and its associated reflector for focusing the energy. See also waveguide, loop antenna, beavertail antenna.
Industry:Weather
An aneroid barometer arranged so that the deflection of the aneroid capsule actuates a pen that graphs a record on a rotating drum. The magnification of the deflection of the capsule may be adjusted so that records of small fluctuations in pressure may be obtained. The aneroid barograph is subject to the uncertainties of the aneroid barometer and therefore must be calibrated periodically. See also barograph, microbarograph.
Industry:Weather
The amount of moisture present in the soil at the beginning of a storm event, frequently expressed as an index corresponding to the weighted average of daily rainfalls for a given period of time preceding the storm event.
Industry:Weather
A weighted summation of daily precipitation amounts, used as an index of soil moisture. The weight given each day's precipitation is usually assumed to be an exponential or reciprocal function of time with the most recent precipitation receiving the greatest weight. The antecedent precipitation index method is commonly used to initialize some rainfall models.
Industry:Weather
1. The region between the Antarctic Polar Front and the Continental Water Boundary. 2. Geographically, the region between the Antarctic Circle (66°32′S) and the South Pole. Climatically, the limit of the zone may be set at about 60°S, poleward of which the prevailing westerly winds give place to easterly or variable winds. Over most of this region the average temperature does not rise above 0°C (32°F) even in summer.
Industry:Weather
