DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

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
winddirectioninthenorthernhemisphere. Ifthe
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
© 2001 by CRC Press LLC
in 1963. For a spherical grain Coble found
ε= DGBδσ
αd 3 kT
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, 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/d 3 ).
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 Swaves
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⊥) tothefield. 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 −12 T 5/2 Wm −1
K −1 (the Spitzer conductivity). The T 5/2 dependence
of κ0 makes energy transport by thermal
conduction negligible for low temperature