- 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, ...
An analysis technique that makes use of radial velocity measurements from two or more Doppler radars or lidars to determine the wind field within an area of precipitation or any other region of space in which there are adequate radar targets. Observations are made from two or more separate vantage points of the radial velocities of echoes from a given region of the atmosphere. Typically, the radial components are combined to deduce the field of the horizontal wind vector on one or more surfaces in the atmosphere. The surfaces may be those that are actually scanned (often by coplane scanning) or a series of horizontal planes. The three-dimensional wind vector may then be estimated by applying the continuity equation, which requires computing the field of horizontal divergence at each of the altitudes within a layer and integrating the divergence over altitude using assumed values of the vertical velocity at the top or bottom of the layer as boundary conditions.
Industry:Weather
A radar capable of simultaneously receiving signals with polarizations identical and orthogonal to that of the transmitted signal. Compare dual-polarization radar, polarimetric radar, and polarization-diversity radar.
Industry:Weather
In a psychrometer, the thermometer that has a dry bulb and therefore directly measures air temperature. See wet-bulb thermometer.
Industry:Weather
A low-level mesoscale boundary or transition zone hundreds of kilometers in length and up to tens of kilometers in width separating dry air from moist air. The length of the dryline is related to large-scale terrain or large-scale weather system features, whereas its width is related to mesoscale processes. In its quiescent state, the dryline may be considered the intersection of the top of a low-level moist layer with large-scale features of sloping terrain. In this state the shallow layer of moisture near the higher terrain is eroded by turbulent mixing with daytime heating. Moisture gradients are additionally strengthened by horizontal convergence resulting from downward transport of horizontal momentum in the dry air. In a more dynamically active state the dryline often advances away from the higher terrain as an integral component of an extratropical cyclone or frontal wave. In such cases it extends equatorward from the cyclone or wave. In this state moisture gradients and boundary motion are largely influenced by downward transport of horizontal momentum resulting from larger-scale sinking in the dry air. The dryline is found all over the world. In the United States the dryline, which marks the boundary between moist air from the Gulf of Mexico and dry continental air from the west, is found in the Plains region. It is most often present during the spring, where it is often the site of thunderstorm development. Typically the dryline in the United States advances eastward during the day and retreats westward at night.
Industry:Weather
Technically, the temperature registered by the dry-bulb thermometer of a psychrometer. However, it is identical to the temperature of the air and may also be used in that sense. Compare wet-bulb temperature.
Industry:Weather
1. An adiabatic process in a hypothetical atmosphere in which no moisture is present. 2. An adiabatic process in which no condensation of its water vapor occurs and no liquid water is present. See dry-adiabatic lapse rate.
Industry:Weather
Years in which streamflow records show runoff significantly less than the mean annual runoff.
Industry:Weather
In synoptic meteorology, a pronounced protrusion of relatively dry air into a region of higher moisture content, sometimes associated with the jet stream or jet streaks at upper levels. This term is more frequently used than its opposite, moist tongue.
Industry:Weather
A thermodynamic variable similar to potential temperature, except that the concept of static energy assumes that any kinetic energy is locally dissipated into heat. The amount of this dissipative heating is often negligible. When dry static energy, s, is expressed in units of kJ kg−1, the resulting values are of order 300 kJ kg−1, which reinforces the analogy with potential temperatures in units of Kelvin. Dry static energy is conserved during unsaturated vertical and horizontal motion, and is defined as
where cp is the specific heat capacity of air at constant pressure, T is absolute temperature, g is gravitational acceleration, and z is height. The reference height can be arbitrary; it is sometimes taken as z = 0 at P = 100 kPa to be consistent with potential temperature, or it can be defined relative to the local ground or sea level. Compare moist static energy, liquid water static energy, saturation static energy.
Industry:Weather
