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coastal jet

particle forces due to electrical charges are significant compared to particle weight.

clear air turbulence (CAT) Vigorous smallscale motions within the lowest kilometer of the atmosphere. Most clear air turbulence is the result of small-scale wavelike undulations that develop spontaneously when the vertical shear of the horizontal flow exceeds some critical value.

cleft, polar See cusp, polar.

climate regimes (Charney and DeVore, 1979). The equilibrium states in the extratropical circulation in the atmosphere.

climatic optimum Mid-Holocene event in which summer temperatures in the Northern hemisphere averaged 1 to 2◦C above current temperatures. Dated as the period approximately 8000 to 5000 years ago.

closed magnetosphere A model of a magnetosphere (usually the Earth’s), in which all planetary magnetic field lines are confined inside some surface, usually identified with the magnetopause. The Earth’s magnetosphere resembles a closed magnetosphere, except for two details: (1) on the night side, field lines extend to great distances and no well-defined closure surface has been observed there; (2) indications exist that a small amount of interconnection usually exists. See open magnetosphere.

closed universe A model of the universe that is finite in total volume and age. It evolves from a “big bang” to a point of maximum expansion before contracting back to a “big crunch” of high density and temperature.

cloud classification A scheme of distinguishing and grouping clouds based on their appearance, elevation, and the physical processes generating them. The World Meteorological Organization classifies 10 genera in three major groups — cumulus, stratus, and cirrus, by criteria essentially according to the cloud formation processes. The major cloud genera are, cirrus (Ci), cirrocumulus (Cc), cirrostratus (Cs), altocumulus (Ac), altostratus (As), nimbostratus (Ns), stratocumulus (Sc), stratus (St ), cumulus

(Cu), and cumulonimbus (Cb). Clouds can also be referred to, according to their composition, as water clouds, ice clouds, or mixed clouds.

clump star A metal-rich star of a few solar masses that has begun helium burning. Because of the difference in opacity, such stars do not reach the giant branch but instead spend a long period of time in the red clump in the HR diagram, B − V = 1mag, and M = 0mag.

CNO cycle (or tricycle) A set of nuclear reactions in which hydrogen is fused to helium, with the liberation of about 7 × 1018 ergs per gram, 5 to 10% of which is lost in neutrinos, depending on the precise temperature at which the reactions occur, generally in the range 15–25 ×106 K. These reactions, which require the presence of carbon, nitrogen, or oxygen as catalysts, are the primary source of energy for stars larger than about 2 solar masses during their main sequence lifetimes and for all stars during the red giant phase. They are the primary source of nitrogen in the universe and contribute to the production of 13C , 15N , 17O , 18O, and, through extensions

to heavier catalysts at higher temperatures, probably also to 19F , 21Ne , 22Ne , 23Na, and perhaps 26Al.

The primary reaction sequence is (see nuclear reactions for explanation of the symbols):

12C(p, γ )13N(e+νe)13C(p, γ )14N(p, γ ) 15O(e+νe)15N(p, α)12C ,

thus the net effect is to convert four protons (hydrogen atoms) to one helium nucleus or alpha particle, returning the 12C to its original form. Other closures include

15N(p, γ )16O(p, γ )17F (e+νe)17O(p, γ ) 18F (e+νe)18O(p, α)15N .

See nuclear reactions.

cnoidal wave A nonlinear theory for periodic waves, attributed to Korteweg and Devries (1895), in which the water surface profile is expressed in terms of a Jacobian elliptical integral, cn(u).

coastal jet a coastal current system that intensifies toward the coast.

© 2001 by CRC Press LLC

coastally trapped waves

coastally trapped waves Waves generated by wind blowing over a stratified ocean with a shelf topography. These are hybrid waves with characteristics of both Kelvin and continental shelf waves. In the northern hemisphere, waves propagate alongshore with the coast on the right.

coastal ocean Shallow water generally situated over continental shelves; often, but not always, case 2 waters. See case 2 water.

coastal upwelling or downwelling The resultant ocean volume transport in the Ekman layer is at right angles to and to the right of the wind direction in the northern hemisphere. If the wind blows parallel to the coast and is directed with the coast on the right/left in the northern/southern hemisphere, water in the Ekman layer will tend to move away from the coast and will be replaced by water moving upward from below the layer. This is called the coastal upwelling. Regions particularly noted for coastal upwelling are the coast of Peru, the U.S. West Coast, and the coasts of Northwest and Southwest Africa. There is also upwelling off Somalia and Arabia during the Southwest Monsoon.

Likewise, if the wind blows parallel to the coast and is directed with the coast on the left/right in the northern/southern hemisphere, water in the Ekman layer will tend to move toward the coast and will move downward to replace water below the layer. This is called the coastal downwelling.

Coastal Zone Color Scanner (CZCS) A multi-spectral line scanner operational from October 1978 to June 1986, which had four channels devoted to ocean color, each of 20 nm bandwidth and centered at 443, 520, 550, and 670 nanometers.

cobble A sediment particle between 64 and 250 mm in diameter (definitions vary). Generally rounded due to abrasive action.

coble creep (grain-boundary diffusion creep)

A deformation mechanism for the diffusion creep of a fine-grained polycrystal, in which the creep rate is controlled by diffusion along the grain boundary. It was first proposed by Coble

in 1963. For a spherical grain Coble found

= DGB δσI

ε

αd3kT

where (ε) is the creep rate, DGB is the grain boundary self-diffusion coefficient, δ is the thickness, σ is the differential stress, d is the grain size, I is the atomic volume, k is Boltzmann’s constant, α is a numerical coefficient depending on the grain shape and the boundary conditions for σ , and T is the temperature. It is a linear rheology (n = 1, n is stress sensitivity of creep rate at steady-state stage) with a high sensitivity to grain-size (strain rate depends on the grain size as ε 1/d3).

cobpoint Short for “connection of observer point”, describing the point on a shock to which the observer is connected magnetically. See connection longitude.

coda wave A wave group following P- and S- waves on a seismogram. For a near earthquake, there are many cases in which the directions of arrival of coda waves cannot be determined. The coda waves are considered to consist mainly of incoherent waves scattered in a small-scale heterogeneous structure in the Earth. The spectrum of coda waves hardly depends on hypocentral distances or ray paths of seismic waves. Coda Q as a measure of energy redistribution and magnitude of earthquakes can be determined from, respectively, decreasing rate of amplitude of coda waves and their duration time.

coefficient of thermal conductivity A measure of the ability of a material to transport thermal energy. In solar physics the coefficient of thermal conductivity, usually denoted κ, is used in the calculation of heat flux transfer in a fully ionized medium. When a magnetic field is present, the coefficient of thermal conductivity depends on whether one is considering the heat transfer parallel (κ ) or perpendicular

(κ ) to the field. In the solar corona, the ratio of these two coefficients is κ /κ 10−13,

and so for most situations, κ is ignored and we have κ = κ0 = 9 × 10−12T 5/2 W m−1 K−1 (the Spitzer conductivity). The T 5/2 de-

pendence of κ0 makes energy transport by thermal conduction negligible for low temperature

© 2001 by CRC Press LLC

colored dissolved organic matter (CDOM)

plasmas, such as the lower chromosphere and photosphere.

coesite A dense, heavy form of silica, formed at extremely high pressures and temperatures (40 kb at 700◦C to 1700◦C). Coesite is found naturally only in meteorite impact craters. Stishovite, an even higher temperature, higher pressure polymorph of quartz, is also found associated with impact craters.

cohesionless Without cohesion; used to describe sediments, such as sand, that have little tendency to cling together when completely dry or wet (surface tension will hold moist particles together if partially wet).

cohesive sediment Sediment in which particles cling together due to electrical charges on particle edges or sides. These forces are significant compared to particle weight. Clays represent the best example of cohesive sediments.

cold dark matter See dark matter, cold.

cold front The front line along which a wedge of cold sector air underruns and displaces the warm sector mass. The gradient of the upper surface of the cold air is steep, about 1/25 to 1/100. Along the cold front there is a strong instability that causes cumulonimbus clouds with rain and thunder. When the cold front passes, weather changes with significant temperature decrease, increasing pressure, and wind veering to northerly or north-westerly in the northern hemisphere.

cold plasma Formal description of a plasma neglecting the thermal motion of the particles. Such cold plasma is the basic assumption in magnetohydrodynamics: it allows the description of a plasma as a fluid with all particles having the same speed, the bulk speed, and is sufficient to derive concepts, such as frozen-in fields, magnetic pressure and tension, and reconnection.

Coleman–Weinberg potential Spontaneous symmetry breaking field-theory models predict that topological defects (magnetic monopoles, cosmic strings, domain walls) could survive

from the early universe. However, they require that a scalar field φ evolves in a potential such that its minimum (which determines the actual vacuum) is reached for non-vanishing values of φ. Ad hoc fixing of such an arbitrary potential appears rather unnatural. However, Coleman and Weinberg realized in 1973 that in some cases, quantum radiative corrections to an otherwise more natural potential could generate the required shape for symmetry breaking. See Higgs mechanism, spontaneous symmetry breaking.

collision boundary

See convergent bound-

ary.

 

collisionless shock

The momentum trans-

port by collisions plays a crucial role in the formation of gas-dynamic shocks. In the rarefied plasmas of space, too few collisions occur between the constituents of the plasma to provide efficient momentum transport and allow for shock formation. Nonetheless, shocks do exist in space plasmas. These shocks are called collisionless shocks; here the collective behavior of the plasma is not guaranteed by collisions but by the collective effects of the electrical and magnetic properties of the plasma, which allow for frequent interactions between the particles and, consequently, also for the formation of a shock wave.

color-color diagram A plot of one color index vs. another color index of a collection of stars. In the Johnson photometry system, the commonly used color-color diagram plots the U-B color vs. the B-V color. The placement of a star on this diagram is a function of its intrinsic colors (which are a measure of the star’s temperature) and the strength of the interstellar reddening. The effect of reddening is to move stars along a line of increasing U-B and B-V values.

colored dissolved organic matter (CDOM)

High-molecular-weight organic compounds (humic and fulvic acids) formed from the decomposition of plant tissue; they strongly absorb light at the blue end of the spectrum and can give water a yellowish color at high concentrations.

© 2001 by CRC Press LLC

color excess

color excess A measure of the reddening of starlight due to small intervening interstellar dust grains. It has been found for most interstellar dust clouds that the extinction of light is proportional to the amount of reddening that a given interstellar cloud causes.

AV = 3.2 .

E

AV is the visual extinction (obscuration) of light in magnitudes, and E is the color excess of B and V magnitudes, given by the intrinsic color index subtracted from the measured color index

E = (B − V ) − (B − V )o

where (B−V) and (B−V)o are the measured and expected color indices, respectively, of a star of a known temperature (see color index). Since the ratio of extinction to reddening is known, then the luminosity of the star can be derived and hence the distance to the star.

color index The difference between a star’s apparent magnitude at some given wavelength to that at another (longer) wavelength. A typical color index used is B–V, where B and V are the apparent blue and visible magnitudes measured with standard filters at 4200 and 5400, respectively. The color index is independent of distance and gives a measure of a star’s color temperature, that temperature which approximates the radiation distribution of the star as a black body (see color temperature). For any given stellar type, there is an expected color index, calculated by assuming a black body temperature for the star. Any difference between the observed color index and the measured color index of a star is due to interstellar reddening. See color excess.

color-magnitude diagram

See HR (Hertz-

sprung–Russell) diagram.

 

color temperature The temperature that describes a black body radiation distribution based on the intensity ratios at two or more wavelength intervals (or “colors”). One reason that the radiation distribution from stars deviates from that of a black body is that atoms and molecules in the stellar atmosphere deplete radiation from the

continuum for spectral line formation. Then a least squares fit of a Planck curve to the stellar spectrum will underestimate the radiation temperature of the star. However, since the shape of a black body curve for any temperature is the same, the ratio of the intensity at two wavelength intervals judiciously chosen to avoid strong absorption features will give a temperature that more closely describes the radiation distribution that the star is actually putting out.

coma In a comet, the region of heated gas and dust surrounding the nucleus of the comet, distinct from the tails which are generated by nuclear and coma material driven off by solar wind and solar radiation pressure. The gas in the coma may be ionized, and its composition can vary with distance from the comet as the different molecules undergo photo-dissociation with time. The coma can reach many millions of kilometers in radius. In optics, an image defect in which the image of a point consists of an offcenter bright spot in a larger, fainter “coma”.

comet A small solar system object composed substantially of volatile material, which is distinctive because of its rapid motion across the sky and its long tail(s) of gas and dust emitted from the body. An accurate description of a comet is a “dirty snowball”, “dirty iceberg” since comets contain some rocky material but are primarily composed of ice. The rocky-icy center of a comet is called the nucleus. Comets usually orbit the sun in highly elliptical orbits. As the comet nears the sun, the increased temperature causes the ice in the nucleus to sublimate and form a gaseous halo around the nucleus, called the coma. Comets often possess two tails: a dust tail that lies in the orbit behind the comet generated by surface activity, and a brighter, ionized gas tail, that points away from the sun, driven by solar wind. Long period comets (periods greater than 200 years) are thought to originate in the Oort cloud, a spherical shell surrounding the Earth at distances exceeding 50,000 AU. They are perturbed by the planets (especially Jupiter) to fall in toward the sun. Their orbits typically have random inclinations and very large eccentricities; some hyperbolic orbits have been observed. Short period comets apparently arise in the Kuiper Belt, in the zone

© 2001 by CRC Press LLC

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