- 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 mirage in which the image or images are displaced downward from the position of the object. If only a single image of distant objects is seen, then the term sinking is often applied: A horizontal surface appears to curve downwards with increasing distance and terminate in a relatively nearby optical horizon. The inferior mirage is most striking when it exhibits two images; the second, lower image is always inverted and of reduced magnification. Sometimes textbooks suggest that there is but a single image: the lower, inverted one. The upper erect image is claimed to be the object. However, both are images, and have positions and magnifications that differ from that of the object. Also, the lower inverted image is sometimes misinterpreted as having resulted from a reflection and when this is seen over land, it leads to the assumption that there must be water in the distance causing the reflection. This is the origin of the long association of the mirage and illusory water, and this leads to the assumption that water is present on a dry surface. The mirage owes its name (from se mirer, to look in a mirror) to this impression of arising from a reflection, having been named by French mariners for images seen at sea. For vertical objects seen beyond the optical horizon, typically the lower portion of the object cannot be seen, and an upper portion of the object is seen twice: erect, and inverted. The farther away the object, the more of the lower portion of it will have vanished so that, for example, the upper decks of a distant ship might appear erect and inverted and apparently floating above and disconnected from the optical horizon while the lower decks will not be seen at all. Sometimes a scene such as this is misinterpreted as resulting from a superior mirage by a person who thinks the ship's images have been lifted up from the horizon. Actually, in this case, everything is displaced, but the horizon has merely been displaced more. Inferior mirages occur over a surface when the temperature decreases with height. The formation of a two-image inferior mirage also requires that the temperature gradient decrease with height. These conditions are met when the surface is relatively warm, resulting in an upward heat flux, such as over sun-warmed ground or a lake at night. See sinking, stooping; compare superior mirage, towering, looming.
Industry:Weather
A measure of the angle from horizontal of a line that extends through the geographic centers of circulation of an anticyclone on multiple levels in the atmosphere.
Industry:Weather
A method to approximate the effects of turbulence by retaining a prognostic equation for mean variables (such as wind or temperature), but where a profile shape of those mean variables is assumed a priori. For example, in the boundary layer, if the daytime profile of potential temperature is assumed to be uniform with height, then only one temperature forecast equation is needed for the whole layer. Similarly at night, if an exponential shape is assumed for the potential temperature profile in the stable boundary layer, then only one temperature forecast equation is needed for the cooling at the surface. This approach is less computationally expensive than solving forecast equations at every height within the mixed layer or stable boundary layer. See closure assumptions, first-order closure, higher-order closure, nonlocal closure.
Industry:Weather
A method of fitting a frequency curve to an observed series of floods on the assumption that the logarithms of the variate are normally distributed.
Industry:Weather
A method of estimating a quantity, such as the mean streamflow velocity or mean sediment concentration along a vertical profile, whereby a measurement instrument is raised and lowered across the profile at a constant rate to achieve a uniform sampling of the profile.
Industry:Weather
A method of analysis of a wind sounding at a station. Contrary to mathematical convention, individual wind vectors at selected levels are plotted, typically on a polar coordinate diagram, from the region of the diagram toward the direction from which the wind blows. The lengths of the vectors are proportional to the corresponding wind speeds. The sense of each vector is toward the origin. The lines joining the starting points of airflow at successive levels form a hodograph (or hodogram). Each such line corresponds to the wind shear vector in the layer concerned.
Industry:Weather
A measure of the angle from horizontal of a line that extends through the geographic centers of circulation of a cyclone on multiple levels in the atmosphere.
Industry:Weather
A major interval of geologic time during which extensive ice sheets (continental glaciers) formed over many parts of the world. The best known ice ages are 1) the Huronian in Canada, occurring very early in the Proterozoic era (2700–1800 million years ago); 2) the pre-Cambrian and early Cambrian, which occurred in the early Paleozoic era (about 540 million years ago) and left traces widely scattered over the world; and 3) the Permo-Carboniferous, occurring during the late Paleozoic era (from 290 million years ago), which was extensively developed on Gondwana, a large continent comprising what is now India, South America, Australia, Antarctica, Africa, and portions of Asia and North America. The term ice age is also applied to advances and retreats of glaciers during the Quaternary era.
Industry:Weather
A major branch of bioclimatology that deals with effects of climate upon man. Currently, its major emphasis is on 1) the heat balance of the human body under different conditions of air temperature, humidity, and wind; 2) the effects of radiation, especially nuclear and ultraviolet, on genetics and general health; 3) the effects of atmospheric conditions and of types of changes of weather and climate on human health, vigor, and disease; and recently, 4) the effects of electrical conditions, including the atmospheric potential gradient and longwave radiations.
Industry:Weather
A long, thin ice crystal, axis coincident with the c axis of ice and with the cross section perpendicular to its long dimension being, at least in part, hexagonal. Ice needles grow in a narrow range of temperature near −4°C and also at much lower temperatures, below −25° to −50°C depending on ice supersaturation.
Industry:Weather
