DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

inelastic collision Collision between two or
more bodies in which there is loss of kinetic
energy.
inelastic scattering of radiation Scattering
in which the wavelength of radiation changes
because radiant energy is transferred to the scatterer.
inertia In Newtonian physics, the tendency
of a material object to remain at rest, or in a state
of uniform motion.
inertia coefficient Also referred to as a mass
coefficient; appears in the Morison Equation for
description of wave-induced force on a vertical
pile or cylinder. Denotes the force that arises
due to the acceleration of the fluid around the
cylinder. A second term denotes the force due
to the square of the instantaneous velocity and
includes a drag coefficient.
inertial-convective subrange For wave
numbers k well below LB −1 , the molecular diffusivity
of heat or salt does not influence the
spectrum very much, and so the spectra are similar
to the velocity spectrum E(k), which falls off
proportional to k −5/3 (inertial-convective subrange).
For smaller scales, velocity fluctuations
are reduced progressively by viscosity, but the
diffusivity of heat or salt is not yet effective
(viscous-convective subrange).
inertial coordinate system An unaccelerated
coordinate system in which the laws of
Newton and the laws of special relativity hold
without correction. In the absence of gravity,
this coordinate system can be extended to arbitrarily
large distances. In the presence of gravity,
such a coordinate system can be erected locally,
but cannot be extended beyond lengths
corresponding to the typical tidal scale of r =
c/ √ Gρ, where c is the speed of light, G is Newton’s
gravitational constant, and ρ is a measure
of the matter density.
inertial frequency When waves are long
compared with the Rossby radius, the frequency
is approximately constant and equal to the Coriolis
parameter, f , or twice the Earth’s rotation
rate. In this limit, gravity has no effect, so fluid
© 2001 by CRC Press LLC
inertial subrange
particles are moving under their own inertia.
Thus, f is often called the inertial frequency.
The corresponding motion is called the inertial
motion or inertial oscillation; the paths are
called inertial circles. Likewise the wave with
this frequency is known as the inertial wave.
inertialinstability Theinstabilitythatoccurs
when a parcel of fluid is displaced radially in an
axisymmetric vortex with negative (positive) absolute
vorticity (planetary vorticity plus relative
vorticity) in the northern (southern) hemisphere.
inertial mass The mass that opposes motion.
In general, for small accelerations, a = F/m,
where m is the inertial mass. The inertial mass
is usually contrasted to the passive gravitational
mass, which is a factor in the Newtonian force
law, and to the active gravitational mass, which
generates the gravitational field. In Newtonian
gravitation, and in general relativity, all these
masses are proportional, and are set equal by
convention.
inertial oscillation A fluid particle with an
initial velocity v but free of force in the Northern
Hemisphere will be bent by the inertial Coriolis
force of magnitude 2 sin θ to its right, where
is the angular velocity of Earth rotation around
the North Pole and θ is the local latitude. In the
absence of background currents, the particle’s
trajectory is a circle with a radius of v/2 sin θ.
The particle returns to its original position in
1/(2 sin θ) days (inertial period). Inertial oscillations
are often observed in the ocean after
strong wind events like hurricanes.
inertial subrange Part of the turbulent kinetic
energy spectrum where turbulent kinetic
energy is neither produced nor dissipated by
molecular diffusion, but only transferred from
larger to shorter length scales by initial forces
(see also turbulence cascade). Wavenumbers
in this part of the spectrum are much larger
than the energy containing scales of turbulence
and shorter than the Kolmogorov wavenumber
kη = ɛ/ν 3 1/4 at which kinetic energy is dissipated
into heat. For sufficiently high Reynolds
numbers, this part of the spectrum is nearly
isotropic and is independent of molecular viscosity.
The shape of the energy spectrum (see
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