DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

law-of-the-wall scaling
in the surface layer below the wave-affected surface
layer. See law-of-the-wall scaling.
law-of-the-wall scaling In a law-of-the-wall
boundary layer zone, where the logarithmic velocity
profile applies, a layer’s turbulence depends
on the surface stress τ0 (or equivalent
u∗ =(τ0/ρ) 1/2 ) and on depth z. Dimensional
analysis provides the law-of-the-wall scaling relations
(often simply called wall-layer scaling)
given by the table.
laws of black hole physics Classical
black hole solutions of general relativity (see
Schwarzschild metric, Reissner–Nordströ m
metric, Kerr–Newman metric) obey four laws
which are analogous to the laws of thermodynamics:
1. Zeroth law: The surface gravity κ is constant
on the horizon.
2. First law: The variation of the ADM mass
M is given by the Smarr formula
δM = κ
δA+δJ +δQ ,
8π
where A is the area of the horizon, J is the angular
momentum of the black hole, is the angular
velocity at the horizon,Q is the charge of
the black hole, and is the electric potential at
the horizon.
3. Second law: No physical process can decrease
the area A of the horizon,
δA ≥ 0 .
4. Thirdlaw: Thestatecorrespondingtovanishing
surface gravity κ= 0 cannot be reached
in a finite time.
From the zeroth and third law, one notices
a similarity between the surface gravity κ/2π
and the temperature of a classical thermodynamical
system. The ADM mass M behaves
like the total energy (first law) and the area
A/4 as an entropy (second law). The analogy
was further substantiated by the discovery due
to S. Hawking that a black hole in a vacuum
emits radiation via quantum processes with a
Planckian spectrum at the temperature κ/2π.
See ADM mass, black hole, Kerr–Newman metric,
Reissner–Nordströ mmetric, Schwarzschild
metric, surface gravity.
© 2001 by CRC Press LLC
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layering See double diffusion.
leader spot A sunspot or sunspot group lying
on the western side of an active region complex,
i.e., leading in the direction of solar rotation.
The largest spots tend to form in the side of the
bipolar group that is preceding in the direction
of solar rotation. The growth of the longitudinal
extent of an active region as it develops
is achieved primarily through the rapid forward
motion of the preceding spot.
leap second A second inserted in Universal
Time at the end of June 30 or December 31 when,
in the judgment of the Bureau International des
Poids et Mesures, its addition is necessary to
resynchronize International Atomic Time with
Universal Time, specifically UT1. The latter is
determined by the Earth’s rotation, which is generally
slowed down by oceanic and atmospheric
tidal friction. Leap seconds have been added
since June 30, 1972.
leap year A year in the Julian and Gregorian
calendars in which an extra day is inserted
(February 29) to resynchronize the calendar with
sidereal time.
Leda Moon of Jupiter, also designated JXIII.
Discovered by C. Kowal in 1974, its orbit has an
eccentricity of 0.148, an inclination of 26.07 ◦ ,
and a semimajor axis of 1.109 × 10 7 km. Its
radius is roughly 8 km, its mass 5.7 × 10 15 kg,
and its density 2.7 g cm −3 . Its geometric albedo
has not been well determined. It orbits Jupiter
once every 238.7 Earth days.
lee wave The atmospheric wave that is generated
in the lee of isolated hills. Typical values
of the wavelengths observed in the atmosphere
are 10 to 20 km.
left-lateral strike-slip fault The horizontal
motion on this strike-slip fault is such that an
observer on one side of the fault sees the other
side moving to the left.
Lemaître, Georges (July 17, 1894 – June 20,
1966). Belgian priest, mathematician, physicist,
and astrophysicist. He is most famous for his
rediscovery of one of the cosmological models