intercommutation

inshore The portion of a beach profile lying between the foreshore and offshore.

insolation Shortwave solar radiation (UV, visible, near infrared) per unit area that is received in the Earth’s atmosphere or at its surface, taking into account the angle of incidence to the horizontal.

Institute of Space and Astronautical Studies (ISAS) Japanese space agency responsible for a number of successful scientific spacecraft, including the solar missions Hinotori and Yohkoh.

integrated Sachs–Wolfe effect In cosmology, in the linear regime where fluctuations can be considered small perturbations on an expanding homogeneous isotopic cosmology, the contribution to temperature anisotropies from varying gravitational potentials along the line of sight. For a flat universe with no cosmological constant, the gravitational potentials do not evolve with time and this effect is zero. In open and flat models with cosmological constant (see Friedmann models) it can dominate over the gravitational potential variations across the last scattering surface.

intensity The radiant power in a given direction per unit solid angle per unit wavelength interval [W sr−1 nm−1].

interaction of galaxies The gravitational attraction between two or more galaxies, which can induce notable modifications in their morphology, as well as in their photometric and spectroscopic properties. Interacting galaxies are often classified as peculiar, since their morphology does not fit the criteria of any of the main classification schemes for galaxies. The effect of interaction among galaxies depends strongly on their mutual distance from a companion galaxy, depending on the inverse cube of the distance. Extensive observation, as well as computational simulation, suggests that for disk galaxies, the effects of interaction on morphology encompass the formation or enhancement of a spiral pattern, the formation of a bar, and, in more extreme cases, the formation of tidal tails, or of a prominent outer ring, as in ring

galaxies or, ultimately, the production of a remnant (after a merger) which resembles an elliptical galaxy. Collisions involving only elliptical galaxies may lead to the production of ripples, extended halos, and asymmetries in the photometric profiles, but they do not produce such spectacular features as tidal tails. Interaction of galaxies has been linked to an enhancement of star formation in the host galaxies and, more speculatively, to the occurrence of quasar-type nuclear activity. See elliptical galaxies, galaxy, spiral galaxy, starburst galaxy.

intercloud medium The warm (≈ 3000 K) low density (≈ 10−2/cm3) gas in rough pressure equilibrium with interstellar clouds.

intercommutation In the physics of cosmic strings, after a cosmic phase transition with the generation of cosmic strings, the resulting network is free to evolve and multiple interactions between single strings will take place. For the simplest (Abelian–Higgs) model, numerical simulations show that two strings will, in general, interchange extremes when crossing. This exchange of partners is intercommutation (also sometimes referred to as reconnection). In strings that might be generated from more complicated fields (non-Abelian π1(M)) string entanglement may take place, due to the fact that exchange of partners is topologically forbidden. See cosmic string, cosmic topological defect, cusp (cosmic string), kink (cosmic string).

(c)

(a)(b)

String interactions: (a) intercommutation, with the possible appearance of kinks and cusps, (b) no intercommutation, i.e., the strings cross each other and are left essentially unaffected, and (c) entanglement.

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43π µr13.

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-controlled creep In rheology, a deformation 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 σ 2 D κT µbd

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

(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

2

ds2 = −

3 1 − R12

−

1 − R2

dt2

r2

r2

+dr2

1− Rr22

+ r2 dθ2 + sin2 θdφ2

describing the gravitational field interior to a static, incompressible perfect fluid sphere of ra-

dius r1, density µ =

3

, and pressure

8πR2

µ

−

1 −

r12

.

1 −

r2

p

=

R2

R2

3

−

r12

1 −

1 −

r2

R2

R2

The total mass of the sphere is m =

The pressure is regular at the center provided

r2 < (8/9)R2. This condition sets an upper
1
limit on the mass of the sphere.
intermediate shock	Results from the steep-

ening 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

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International Temperature Scale (ITS-90)

but a rotational discontinuity. The propagation speed parallel to the magnetic field equals the Alfvén speed; thus, the intermediate shock is sometimes also called Alfvén shock.

intermittency Even in non-stratified, homogeneous turbulence, variations of the dissipation of turbulent kinetic energy (ε) and scalar variance (χ) are large and follow lognormal probability distributions. In natural waters, intermittency is larger because, in addition to the inherent intermittency, the production and transport of turbulent kinetic energy is usually variable in time and patchy in space. Due to the variations of the physical processes and intensities leading to turbulence, turbulence parameters, such as ε and χ, are usually not lognormal distributed. The standard deviation of ln(εi) is sometimes called intermittency factor.

internal energy The total energy in a thermodynamic system not associated with bulk motion; an extensive thermodynamic potential U given by

U = ST + P V ,

where S is the entropy, T is the temperature, P is the pressure, and V is the volume of the system. The change of the internal energy is the maximum work that can be extracted from a reversible closed system at constant V . For a reversible process at constant S and V , work stored as internal energy can be recovered completely.

internal friction angle A term used in the study of soil mechanics; denotes the maximum sustainable angle for a pile of the soil. Also referred to as angle of repose.

internal wave In oceanography, a wave that occurs within seawater whose density changes with depth either gradually or abruptly at an interface discontinuity.

International Atomic Time (TAI) A weighted average of atomic clocks in many countries, each having its rate adjusted by a very small amount to bring its rate, as transmitted to sea level (the geoid) by telemetry, to that which it would exhibit if situated on the geoid. Because the combination of the results from many clocks,

weighted according to their estimated accuracy, requires hours or days to calculate, TAI is not available in real time, but signals from several sources, such as NIST and the USNO, are very close to TAI and corrections are available after date. First, “Free-running Atomic Time” (EAL) is produced and then TAI is computed from it after frequency adjustments are applied to correct for instrumental errors in the length of the second, as determined from measurements of primary frequency standards (atomic clocks) at timing laboratories. Like Coordinated Universal Time (UTC), TAI is referenced to the Greenwich meridian time zone. Because it increases continuously, when UTC is held back by the introduction of leap seconds, TAI may be thought of as being equal to UTC + (cumulated leap seconds). Thus, TAI noon precedes Greenwich (UTC) solar noon by that number of seconds. See geoid.

international dateline A broken line running from the north to south pole on the Earth roughly along the meridian at 180◦ East longitude = 180◦ West longitude, 180◦ away from the prime meridian through Greenwich. The line along which a discontinuity in the current date occurs. Legal dates are arranged across this line so that the Eastern side of the line has a date 24 hours earlier than the Western side. Thus, on traveling eastward across this line, the legal date becomes one day earlier, e.g., Sunday August 10, 1997 became Saturday August 9, 1997. For political reasons the legal date line does not follow exactly the 180◦ longitude.

International Geomagnetic Reference Field (IGRF) See harmonic model.

International System of Units (SI) The unit system adopted by the General Conference on Weights and Measures in 1960. It consists of several base units (meter, kilogram, second, ampere, kelvin, mole, candela), plus derived units and prefixes.

International Temperature Scale (ITS-90)

The official international temperature scale adopted in 1990. It consists of a set of fixed points and equations that enable the thermody-

© 2001 by CRC Press LLC

interplanetary dust particles (IDPs)

namic temperature to be determined from operational measurements.

interplanetary dust particles (IDPs) The small debris that exists between the planets. Most of this material comes from comets and from collisions between asteroids. Study of interplanetary dust particles provides information about the primitive material out of which the solar system formed, material which has not been subsequently processed by heat, pressure, and chemical reactions as has happened on the larger bodies of the solar system. Sunlight reflecting off the IDPs gives rise to the zodiacal light and gegenschein.

interplanetary magnetic field	See helio-
spheric magnetic field.
interplanetary magnetic sector	A contigu-

ous region observed in interplanetary space, usually near Earth, where for locally observed magnetic field lines, the ends anchored on the sun have all the same polarity. If those ends are directed towards the sun, the region is a “towards sector”; if away from it, it is an “away sector”. Sector structure is caused by the waviness of the heliospheric current sheet (HCS) and the regions above the sun’s poles and away from the HCS do not experience sector variations as the sun rotates.

Since the Earth’s orbit is inclined to the solar magnetic equator, near sunspot minimum, when the waviness of the HCS is small, the Earth generally samples two different sectors. At times of greater solar activity, when the solar magnetic field is more complex, the HCS becomes rather wavy, and the Earth can cross 4, 6, or even

8 sectors per solar rotation.
interplanetary propagation	The propaga-

tion of energetic charged particles through the interplanetary medium is influenced by the following processes:

(a) pitch-angle scattering of particles at the solar wind turbulence is a stochastic process, described by the pitch-angle diffusion coefficient κ(µ) which depends on pitch-angle µ, particle rigidity, level of interplanetary turbulence, and location. In addition, pitch-angle diffusion coefficients might be different for electrons and

nuclei of the same rigidity. Pitch angle scattering is a stochastic process. See pitch angle diffusion, quasi-linear theory, slab model.

(b)focusing in the diverging interplanetary magnetic field is a systematic process decreasing the particle’s pitch angle as it propagates outward. See focusing.

(c)field-parallel propagation of the particle. See focused transport equation.

(d)convection of particles with the solar wind leads, in particular for particles with speeds in the order of the solar wind speed, to a more efficient propagation outwards rather than inwards. See convection.

(e)adiabatic deceleration leads to a cooling of the cosmic ray gas as it expands with the expanding solar wind that is a transport in momentum. See adiabatic deceleration. The transport equation then reads

∂F (µ, s, p, t)

∂t

streaming:

+

∂

µvF

∂z

convection:

+

∂

1 −

µ2

v2

vsowisecψF

∂z

c2

focusing:

secψ

· (1 − µ2)F

+∂µ 2ζ E + µ

v

∂

v

E

vsowi

differential convection:

∂

d

−

vsowi

cos ψ

rsecψ · µ(1 − µ2)F

∂µ

d

scattering:

∂ κ ∂ E

−

F

∂µ

2

∂µ

E

deceleration:

∂

−

pvsowi·

·

∂p

F

2ζ

(1 − µ2) + cos ψ dr secψµ2

secψ

d

source:

= Q(µ, s, t, s, v)

© 2001 by CRC Press LLC