DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

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 heliospheric
magnetic field.
interplanetary magnetic sector A contiguous
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 propagation
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
© 2001 by CRC Press LLC
248
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)convectionofparticleswiththesolarwind
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
streaming:
convection:
+ ∂
∂z
focusing:
+ ∂
v E ′
∂µ 2ζ E
∂F(µ,s,p,t)
∂t
1 − µ
+ ∂
∂z µvF
2 v2
c2 differential convection:
− ∂
∂µ vsowi
scattering:
deceleration:
vsowisecψF
+ µvsowi
v secψ
· (1 − µ 2 )F
cos ψ d
d rsecψ
− ∂ κ ∂ E
∂µ 2 ∂µ
′
E F
− ∂
∂p pvsowi·
secψ
·
2ζ (1 − µ2 ) + cos ψ d
source:
= Q(µ,s,t,s,v)
· µ(1 − µ 2 )F
dr secψµ2
F