DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

Kolmogorov spectrum
the length scale is expressed by
LK =η=
ν 3
ɛ
1/4
rad m −1
where ν is the viscosity of the fluid and ɛ is the
rate at which energy is dissipated by the smallest
turbulent eddies (see dissipation rate). Values
forη are of the order of millimeters in the ocean
and in the atmosphere. This implies that for
scalesshorterthantheKolmogorovscaleLK, the
turbulent kinetic energy is converted into heat by
molecular viscosityν. LK is often referred to as
the size of the smallest possible eddies to exist
in a fluid for a given level of dissipation and
viscosity.
Kolmogorov spectrum The spectrum of the
turbulent kinetic energy follows in the inertial
subrange (scales smaller than the energycontaining
range of eddies; larger than the
Kolmogorov scale) the characteristic so-called
−5/3-law: φ(k) = 1.56ε 2/3 k −5/3 (see inertial
subrange). The name of the spectrum is due to
Kolmogorov (1941).
Kolmogorov wavenumber Defines the wave
numbers at which the turbulent kinetic energy
is converted into heat by molecular viscosity
ν, i.e., kK = (ε/ν 3 ) 1/4 [rad m −1 ]or kK =
(2π) −1 (ε/ν 3 ) 1/4 [cycle m −1 ]. See Kolmogorov
scale.
Kp index A 3-hourly planetary geomagnetic
index of activity generated in Göttingen, Germany,
based on the K indices from 12 Magnetic
Observatories distributed around the world. The
Kp index is calculated by combining these indices
using local weightings. The Kp index is
often presented as a Bartels musical diagram, a
presentation that emphasises the 27-day recurrent
nature of much geomagnetic activity. See
geomagnetic indices.
KREEP Unusual lunar (and martian) rocks,
with unusual amounts of “incompatible elements”:
K-potassium, Rare Earth Elements,
and P-phosphorous, representing the chemical
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remnant of a magma ocean (caused by impact
or volcanism).
Kruskal extension (1960) The maximal analytic
extension of the Schwarzschild space-time
by the introduction of a coordinate system in
which the coordinate velocity of light is constant.
See maximal extension of a space-time.
krypton (Kr) From the Greek kryptos or
“hidden.” A gaseous element, atomic number
36, one of the noble gasses, discovered by
William Ramsay and M.W. Travers in 1898. Its
naturally occurring atomic weight is 83.80. Natural
krypton is found in the atmosphere at about
1 ppm. Its naturally occurring isotopes are 78Kr, 80Kr, 82Kr, 83Kr, 84Kr, 86Kr. 84Kr is naturally
most abundant.
K star Star of spectral type K. Arcturus and
Aldebaran are K stars.
Kuiper belt Region beyond about 35 AU and
extending to roughly 100 AU, in the ecliptic,
that is the source of most short-period comets.
Originally suspected on theoretical grounds in
the early 1950s, it was not until 1992 that the
first Kuiper belt objects were observed. The
belt is roughly planar, and it is believed that interactions
between Kuiper belt objects and the
giant planets cause belt objects to occasionally
cross the orbit of Neptune. Objects that have
a gravitational encounter with that planet will
either be ejected from the solar system, or perturbed
into the region of the planets. The Centaur
class of asteroids, which orbit the sun in
the region between Jupiter and Neptune, as well
as the planet Pluto/Charon, are believed to have
originated in the Kuiper belt. Unlike the Oort
cloud comets, Kuiper belt objects are thought to
have been formed in situ.
Kuiper belt object, trans-Neptunian object,
Edgeworth–Kuiper object A minor body
that resides in the Kuiper belt. Sizes can range
up to a few hundred kilometers.
Kuroshio See Japan current.