DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

interconnection field
interconnection field A magnetic field component,
derived from a scalar potential (see harmonic
model), added to an empirical model of
the closed magnetosphere to turn it into a model
of the open magnetosphere. It may be added
either to obtain a better fit to data, or to create
a testbed model of the open magnetosphere for
testing various theoretical notions. Often a constant,
southward-directed field is used to obtain
this effect.
interface-controlledcreep Inrheology, adeformation
mechanism for diffusion creep. In an
interface-controlled creep, macroscopic strain
is caused by diffusion mass transport involving
creation and/or deposition of vacancies at grainboundary
and their diffusion, through some
rearrangement of atomic structures at grainboundaries.
Interface-controlled creep assumes
that the interface reaction is fast compared to
diffusion, so the overall rate of deformation is
controlled by grain boundary reaction. One example
is the case where the rate of generation or
absorption of vacancies is controlled by the mobility
of grain-boundary dislocations. The constitutive
equation for interface-controlled creep
can be expressed as
ε=C σ2 D
κTµbd
where D is the diffusion coefficient, b the thickness
of grain boundary, σ the differential stress,
d the grain size, the atomic volume, κ Boltzmann’s
constant, C a numerical coefficient depending
on the grain shape and the boundary
conditions for σ, T the temperature, µ the shear
modulus, and ε the strain.
interference fading Results from interference
between signals arriving at a receiver by
two or more different paths. The multiple paths
may arise from sky wave and ground wave paths,
two polarization modes, and various combinations
of multi-mode sky-wave paths, scattering
from ionization irregularities or combinations
of any of these options. Interference fading is a
collective term for the observed fading statistics
whereas multipath fading specifically describes
the path structure of the received radio signal.
In a more restricted sense, interference fading
© 2001 by CRC Press LLC
246
(sometimes called diffraction fading) may describe
multiple paths formed within the region
of the ionosphere where the radio wave for a single
mode is reflected and the resulting fading is
attributed to local ionization irregularities. Interference
fading occurs with an associated period
of 1 sec or larger. See fading.
interglacial For the last 4 million years covering
the Holocene (recent) and the Pleistocene
epochs, the Earth has been primarily in ice ages.
An interglacial is a period of relative warming.
The last interglacial occurred about 120,000
years ago; the current interglacial began about
20,000 years ago. The record indicates that interglacials
have a length of about 20,000 years.
interior Schwarzschild space-time In general
relativity, the spacetime described by the
metric
ds 2 =
⎛
−⎝3
1 − r2
1
− 1 −
R2 r2
R2 ⎞2
⎠ dt 2
+ dr2
1 − r2
R2
2
+ r dθ 2 + sin 2 θdφ 2
describing the gravitational field interior to a
static, incompressibleperfect fluid sphere of ra-
3
dius r1, density µ =
8πR2
, and pressure
1 −
p = µ
r2
R2
− 1 − r2 1
R2
3 1 − r2 1
R2
− 1 − r2
R2 .
The total mass of the sphere is m = 4π 3 µr3 1 .
The pressure is regular at the center provided
r 2 1 < (8/9)R2 . This condition sets an upper
limit on the mass of the sphere.
intermediate shock Results from the steepening
of an intermediate MHD wave that is a
purely traverse wave with velocity perturbations
perpendicular to both the wave vector ko and
the average magnetic field Bo. Intermediate
shocks can exist only in anisotropic media. In an
isotropic plasma, such as the solar wind, a steepened
intermediate wave does not form a shock