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Английский язык

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Dictionary of Geophysics, Astrophysic, and Astronomy.pdf

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warping (of the neutral sheet or plasma sheet)

Wadati–Benioff zones (Benioff zones)

Zones of deep earthquakes in the subducted oceanic plates. These earthquakes were ﬁrst identiﬁed by Japanese seismologist K. Wadati in 1928. H. Benioff recognized the inclined planar shape of the zones of such deep seismicity.

wake The region downstream from a body moving through a ﬂuid. Vorticity generated as the ﬂow separates from the body is concentrated in the wake. Visible as surface waves in the case of boats moving through water.

wake (cosmic string) As a consequence of the conical structure of the space around a cosmic string, particle trajectories will be deﬂected from their original directions when passing close to the string. The deviation angle is 4πGU (half of the deﬁcit angle on each side of the string) and is due to a pure kinematic effect. Here U = mass per unit length of the string.

Consider now a moving string traversing a given distribution of collisionless matter, like stardust, initially at rest. From the viewpoint of the string it is the dust that moves and dust particle geodesics on opposite sides of the string trajectory will tend to converge. Dust velocities perpendicular to the string motion will be of order 4πGUvsγs, where vs is the velocity of the string, and γs is the corresponding Lorentz factor (1 − vs2/c2)−1/2. This produces a region of relatively large matter density behind the string that after subsequent gravitational clumping will lead to the formation of a sheet-like distribution of matter known as a string wake. Wakes are one of the most characteristic signatures in the generation of large scale structure with fast moving cosmic strings. See Abelian string, cosmic string, cosmic topological defect, deﬁcit angle (cosmic string), wiggle (cosmic string).

Walker circulation A longitude-vertical circulation cell of the tropical atmosphere, with rising motion and high convective activity over the

equatorial Indian and western Paciﬁc Oceans. The downdraft is located over the eastern equatorial Paciﬁc, a direct result of cold sea surface underneath. During an El Niño event when the eastern equatorial Paciﬁc Ocean warms, the rising branch of the Walker circulation shifts eastward to the central Paciﬁc, causing drought over the maritime continent and Australia.

wall terracing The walls of large impact craters are often formed at a steep angle (greater than the angle of repose for the material) and are subject to collapse under the inﬂuence of gravity. This collapse of the wall material creates a terraced appearance to the interior walls of the crater. The collapse of the walls causes the ﬁnal crater to be larger than the original crater and decreases the height of the crater rim. The onset crater diameter for wall terracing provides important information about the strength of the material in which the crater formed.

warm front Along a temperature discontinuous surface, warm air advances to replace cold air being pushed forwards so the warm air slides up and over the cold air to produce steady rain. Slopes of warm fronts are typically about 1/100 to 1/300, and the ascent of air is gradual. Ahead of warm fronts for several hundreds of kilometers there will appear cirrus; then as the warm fronts approach, cirrostratus, lower and thickening altostratus, and heavy nimbostratus will appear one by one. If the warm air mass is unstable, shower or thunderstorm activity may be present. Passage of warm fronts is marked by a rise of temperature, decreasing of relative humidity, clearing of precipitation, cloud or fair, and veering wind.

warping (of the neutral sheet or plasma sheet)

The deformation of the equatorial surface (“neutral sheet”) in the plasma sheet regions of the magnetosphere, caused by the tilt of the Earth’s dipole axis. The midnight section of that surface is displaced northward or southward, in a way that matches the displacement of the midnight section of the equatorial plane of the tilted Earth dipole. However, since the two lobes have equal magnetic ﬂuxes and are expected to have equal magnetic intensity (and hence, equal magnetic pressure), the sections of the neutral sheet near

wash load

the magnetopause are displaced in the direction opposite to that of the midnight section.

wash load Sediment that is carried in suspension in a water column through a section of channel or river, which does not originate in that section of channel. Compare with suspended load, bed load.

water H20, colorless, odorless, tasteless liquid; freezing point (to ice) 0◦C, boiling point (to steam) 100◦C (at standard atmospheric pressure). Pure water has a maximum density approximately 1000 kg/m3 at 4◦C and frozen water (ice) is much less dense than water, with a density of 920 kg/m3. The density of liquid water at 0◦C is 999.85 kg/m3 so ice ﬂoats in ice-cold water. Under normal conditions the latent heat of fusion of water is 3.33 × 105 J/kg, and the heat of vaporization is 2.26 × 1066 J/kg. These very large values act to make the oceans substantial reservoirs of heat and buffers of temperature, and ocean currents can distribute this heat, thereby stabilizing the temperature of the Earth.

water mass In physical oceanography, a body of water with a common formation history. Water masses are usually identiﬁed through physical relationships on a temperature-salinity (T-S) diagram. In addition, some assumption about the degree of spatial and temporal variability during a water mass’s formation is almost always needed as well.

water mega-masers Astrophysical masers of a spectral line at 22.235 GHz due to a rotational transition of the water vapor molecule. Water mega-masers are more luminous than the most luminous galactic masers by a factor of 100. Approximately 20 water mega-masers are known as of early 1998; they have been observed in several active galaxies. Interferometric observations have shown that mega-masers are formed within 1 pc from the active nucleus of a galaxy, indicating that the source of pumping radiation needed to sustain the population inversion is provided by the active nucleus itself.

waterspout A tornado that occurs over the ocean.

water table A surface separating the saturated and unsaturated zones of the subsurface, deﬁned as a surface at which the ﬂuid pressure is atmospheric (or zero gage pressure). The water table is generally measured by installing wells or piezometers into the saturated zone and measuring the water level in those wells.

watt (W) The SI unit of power, equal to J/s.

wave A disturbance propagating through a continuous medium. It gives rise to a periodic motion. A wave transports energy and information but not matter. Depending on the oscillatory motion, waves can be longitudinal (such as sound waves) or transversal (such as surface waves or electromagnetic waves). A wave is characterized by its amplitude (or wave height in surface waves), the wavelength or wave number, the wave period or (angular) frequency, and the phase or group speed.

wave-affected surface layer (WASL) The top layer of the surface boundary layer which is signiﬁcantly affected by the action of the waves. The extent is typically (2k)−1 = λ/4π where k is the wavenumber and λ is the wavelength at the peak of the surface wave spectrum.

wave crest The high point on a periodic wave; a point where phase angle is an integer multiple of 2π.

wavefront A 2-surface on which the wave has the same phase (e.g., a maximum of ﬁeld strength) at a particular time. A wave propagating at a great distance from its source through a vacuum or a uniform medium has very nearly plane wavefronts.

wave-function of the universe Any solution of the Wheeler–DeWitt equation in the superspace (or minisuperspace) of 3-metrics of the whole space-time.

One usually considers the minisuperspace case corresponding to homogeneous and isotropic cosmological models (see Robertson– Walker metric) as a manageable approximation of the full quantum theory of gravity, valid in an early stage of our universe when typical particle energies had already fallen below the Planck

weather modiﬁcation

mass but quantum effects were not yet negligible. Such effects include ﬂuctuations around classical trajectories of the scale factor a of the Robertson–Walker metric and tunneling of a between disconnected Lorentzian regions by passing through a classically forbidden Euclidean stage. What the boundary conditions for the wave-function could be is still an open controversy among several schools of thought. See minisuperspace, Robertson–Walker cosmological models, superspace, Wheeler–DeWitt equation.

wavelength The distance between successive maxima of a wave ﬁeld at any particular instant, or more precisely of one Fourier component of such a ﬁeld.

wave number The wave number k gives the number of waves per unit length. It is related to the wavelength λ as k = 2π/λ. See wave vector.

wave-particle interactions An important component, generally described by quasi-linear theory, in the evolution of particles and waves in a plasma.

wave rose A polar histogram that shows the directional distribution of waves for a site. Generally also scaled to indicate wave height as well.

wave trough The low point in a periodic wave; a point where phase angle is (2n + 1)π, n = 0, 1, 2, . . . .

wave vector The wave vector gives the k

direction of propagation of the wave; its length gives the number of waves per unit length, the wave number. The wave vector is related to the

phase speed by = 2. vph vph ωk/k

weak anthropic principle Minimal statement that since we observe the universe, parameters must be such as to support carbon-based life. See anthropic principle.

weak interaction Any nuclear interaction involving neutrinos or antineutrinos. Weak rates are typically much slower than strong interaction rates, at temperatures and energies relevant

to astrophysics. Hence in any reaction chain, the rate will be determined by the weak interaction rate.

weakly asymptotically simple space-time

A space-time (M, g) is weakly asymptotically simple if there exists an asymptotically simple space-time, such that in it a neighborhood of I (null inﬁnity) is an isometric with an open set of M. See asymptotically simple space-time.

weather At a given time or over a short period, measured in days, the state of the atmosphere, deﬁned by measurement of every meteorological element, such as air temperature, pressure, humidity, wind speed and direction, clouds, fog, precipitation, visibility, etc.; the synthetical status of the distributions of the meteorological elements and their accompanying phenomena; the state of the sky which affects the everyday life of humans, such as cloudy, fair, cold, warm, dry, humid, etc. In aviation meteorological observation, weather means precipitation phenomena such as rain, snow, etc.

weather forecast The prediction of future weather based on the meteorological theory and the basis of observations made from satellite data, radar data, and observation networks on both land and sea, which contains the observed reports from the ground surface to high level atmosphere. With the development of computational technology, numerical weather forecast is the most important weather forecast method. It is a complete objective forecast method and is based on atmospheric dynamical and thermaldynamical physics laws implemented on powerful supercomputers to simulate the future atmospheric for the prediction results.

weather modiﬁcation The intentional change in weather conditions by human action, such as artiﬁcial precipitation, artiﬁcial hail, artiﬁcial cloud dispersal, artiﬁcial fog clearing, artiﬁcial hurricane weakening, artiﬁcial thunder

– lightning suppression, artiﬁcial frost prevention, etc. Inadvertent change in weather conditions by human action, such as urban heat island effects, is excluded from the deﬁnition of weather modiﬁcation. Currently, weather modiﬁcation methods are mainly based on the micro-

Weber– Davis Model

physical instability properties of cloud and fog. For example, there are abundant unfrozen water droplets in cold clouds whose temperature is lower than 0◦C, so seeding glacigenic catalysts can cause the unfrozen water droplets to freeze to ice crystals and speed the forming processes of waterdrops. The released condensational latent heat in such processes can change the thermal and dynamical structure of clouds, to enhance precipitation, to reduce hail, to disperse clouds, to clear fog, or to reduce wind speed of hurricanes. Seeding appropriate sized salt powder can enhance the forming process of rain drops in warm clouds, and thus can enhance precipitation or disperse cloud and fog. Currently, the techniques of artiﬁcial cloud dispersal and fog clearing are mature and used widely on airports, while other weather modiﬁcation methods often lead to unexpected results.

Weber–Davis Model The magnetohydrodynamic theory of angular momentum transport a steady, axially symmetric, magnetized, rotating astrophysical wind.

The theory was originally developed as a tool for analysis of the transfer of angular momentum in the solar wind but has found much broader application in theoretical investigations of stellar winds and star formation. In the most general form of the theory, the ﬂow velocity and magnetic ﬁeld are separated into poloidal and toroidal parts, B = Bp + Bt eφ and V = Vp + Vt eφ, where eφ is the unit vector in the azimuthal direction; these quantities are related through conservation laws corresponding to conservation of mass and magnetic ﬂux,

Bp = λρVp

conservation of total (mechanical plus magnetic) angular momentum

(Vt − λBt /4π) = J (λ) ,

and Faraday’s law for a frozen-in magnetic ﬁeld

(Bt /λρ − Vt ) = Q(λ) .

These invariants hold for each streamline, which may be labeled by λ. is distance from the rotation axis, ρ is the mass density, and J and Q

512

are functions of λ to be determined from boundary conditions.

If the ﬂow describes expansion of a wind, the velocity on each streamline passes through an

“Alfvén point” (λ) where the (poloidal) ﬂow

A √

and Alfvén speeds are equal, Vp = Bp/ 4πρ. It can be shown that the constant of the second conservation equation is J (λ) = A2 , whereis the rotation rate of the central object, and that the angular momentum per unit mass of gas approaches J (λ) inﬁnitely far from the source of the wind. Thus, the magnetic ﬁeld enhances angular momentum transport by providing an effective lever arm of length A.

weight The force of gravity; the force with which an object is attracted to the center of a planet;

W = mg ,

where g is the magnitude of the local acceleration of gravity g = GM/r2, where M is the mass, and r is the distance to the center of the planet; G is Newton’s gravitational constant

g 980 cm/sec2 = 9.8 m/sec2 .

near the surface of the Earth.

weir A structure placed on the bottom of a channel, across which water ﬂows, to control depth or to facilitate measurement of ﬂowrate. A variety of designs are available, including broadcrested and short-crested.

well-graded A term used to describe the distribution of particle sizes in a soil sample. A well-graded soil has a wide range of particle sizes.

wentworth size classiﬁcation A classiﬁcation of sediments based on size (diameter). Ranges from boulders (>256 mm) down to colloids (<0.0024 mm).

Wesselink method	See Baade–Wesselink
method.

westerlies The global wind system blowing west to east in both hemispheres of the Earth, between approximately 35◦ and 65◦ (north or south) from the equator.

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warping (of the neutral sheet or plasma sheet)

Wadati–Benioff zones (Benioff zones)

wake The region downstream from a body moving through a ﬂuid. Vorticity generated as the ﬂow separates from the body is concentrated in the wake. Visible as surface waves in the case of boats moving through water.

Walker circulation A longitude-vertical circulation cell of the tropical atmosphere, with rising motion and high convective activity over the

wash load

waterspout A tornado that occurs over the ocean.

watt (W) The SI unit of power, equal to J/s.

wave-affected surface layer (WASL) The top layer of the surface boundary layer which is signiﬁcantly affected by the action of the waves. The extent is typically (2k)−1 = λ/4π where k is the wavenumber and λ is the wavelength at the peak of the surface wave spectrum.

wave crest The high point on a periodic wave; a point where phase angle is an integer multiple of 2π.

wavefront A 2-surface on which the wave has the same phase (e.g., a maximum of ﬁeld strength) at a particular time. A wave propagating at a great distance from its source through a vacuum or a uniform medium has very nearly plane wavefronts.

wave-function of the universe Any solution of the Wheeler–DeWitt equation in the superspace (or minisuperspace) of 3-metrics of the whole space-time.

wavelength The distance between successive maxima of a wave ﬁeld at any particular instant, or more precisely of one Fourier component of such a ﬁeld.

wave number The wave number k gives the number of waves per unit length. It is related to the wavelength λ as k = 2π/λ. See wave vector.

wave-particle interactions An important component, generally described by quasi-linear theory, in the evolution of particles and waves in a plasma.

wave rose A polar histogram that shows the directional distribution of waves for a site. Generally also scaled to indicate wave height as well.

wave trough The low point in a periodic wave; a point where phase angle is (2n + 1)π, n = 0, 1, 2, . . . .

wave vector The wave vector gives the k

weak anthropic principle Minimal statement that since we observe the universe, parameters must be such as to support carbon-based life. See anthropic principle.

weak interaction Any nuclear interaction involving neutrinos or antineutrinos. Weak rates are typically much slower than strong interaction rates, at temperatures and energies relevant

weakly asymptotically simple space-time

weight The force of gravity; the force with which an object is attracted to the center of a planet;

weir A structure placed on the bottom of a channel, across which water ﬂows, to control depth or to facilitate measurement of ﬂowrate. A variety of designs are available, including broadcrested and short-crested.

well-graded A term used to describe the distribution of particle sizes in a soil sample. A well-graded soil has a wide range of particle sizes.

Wesselink method

westerlies The global wind system blowing west to east in both hemispheres of the Earth, between approximately 35◦ and 65◦ (north or south) from the equator.