DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

winter anomaly
Scale
Wind Condition Speed (MPH) Number
Light Less than 1 0
1–3 1
4–7 2
Gentle 8–12 3
Moderate 13–18 4
Fresh 19–24 5
Strong 25–31 6
32–38 7
Gale 39–46 8
47–54 9
Whole gale 55–63 10
64–75 11
Hurricane Above 75 12
shear. Also it can be divided as the cyclonic
wind shear and anti-cyclonic wind shear.
winter anomaly In ionospheric physics, the
F region peak electron densities in the winter
hemisphere at middle latitudes are usually enhanced
above the summer peak electron densities.
Often, the equinoctial electron densities
are enhanced above both solstices. However, it
is still more common to refer to this as a winter
anomaly. The phenomenon is most evident during
daytime solar maximum. The exact cause
of the anomaly has been attributed to a number
of sources, more recently to changes in atmospheric
chemistry associated with upper atmosphere
winds. See F region.
winter solstice The point that lies on the
ecliptic midway between the vernal and autumnal
equinoxes and at which the sun, in its apparent
annual motion, is at its greatest angular distance
south of the celestial equator. On the day
of the winter solstice, which occurs on about December
21, the length of night time darkness is at
its maximum in the northern hemisphere. After
the winter solstice, the length of daylight time
in the northern hemisphere will increase until
the summer solstice. Because of complex interactions
with heat reservoirs in the atmosphere,
soil, and oceans, the northern hemisphere temperature
continues to decrease for a period of
time after the winter solstice. In the southern
hemisphere, the winter solstice (about Decem-
© 2001 by CRC Press LLC
518
ber 21) is the beginning of summer, the day of
the year with the longest period of sunlight.
Witten conducting string Extensions of the
simplest grand unified models with the formation
of cosmic strings in general involve extra
degrees of freedom which are coupled to the
vortex-forming Higgs field. These may be, for
example, other microscopic fields that could be
responsible for the generation of currents, bound
to the core of the vortices, and that may play a
fundamental role in the dynamics of the defects.
The Witten-type bosonic superconductivity
model is one in which the fundamental Lagrangian
is invariant under the action of a U(1)×
U(1) symmetry group. The first U(1) is spontaneously
broken through the usual Higgs mechanism
in which the Higgs field acquires a nonvanishing
vacuum expectation value. Hence, at an
energy scale ∼ m we are left with a network of
ordinary cosmic strings with tension and energy
per unit length T ∼ U ∼ m 2 , as dictated by the
Kibble mechanism. The Higgs field is coupled
not only with its associated gauge vector field
but also with a second charged scalar boson, the
current carrier field, which in turn obeys a quartic
potential. A second phase transition breaks
the second U(1) gauge (or global, in the case of
neutral currents) group and, at an energy scale
∼ m∗ (in general m∗ < ∼ m), the generation of a
current-carrying condensate in the vortex makes
the tension no longer constant, but dependent on
the magnitude of the current, with the general
feature that T ≤ m 2 ≤ U, breaking, therefore,
the degeneracy of the Goto–Nambu strings.
The fact that the absolute value of the current
carrier field is nonvanishing in the string results
in that either electromagnetism (in the case that
the associated gauge vector is the electromagnetic
potential) or the global U(1) is spontaneously
broken in the core, with the resulting
Goldstone bosons carrying charge up and down
the string. Once generated, these currents are
not affected by any resistance mechanism in the
string core (unlike what would be the case for
ordinary conducting wires) and hence are persistent.
Thus these strings are endowed with some
superconducting properties, although the fact
of being defined inside a core no bigger than
the Higgs Compton wavelength (of order the