DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

turbulence is not two-dimensional, the displacementd1
is not necessarily the distance the water
parcel has traveled vertically (see Thorpe scale).
Thorpe displacements are computed from
measured vertical space series of density. A
sorting algorithm is applied to the sampled density
profile, with ordering beginning at the shallowest
depth, which re-orders the samples in ascending
order. If a sample at positionn is moved
to positionm, the associated entry in the Thorpe
displacement series is then dn.
Thorpe scale Measure of the mean eddy size
in turbulent oceanic flows. The Thorpe scaleLT
is defined as the root-mean-square of the Thorpe
displacement, d,
LT =
d2 1/2 where the over-bar signifies an appropriate spatial
average that depends on the vertical extent
of the turbulent process. If the mean vertical
density gradient is much larger than the mean
horizontal gradient, the Thorpe scale is proportional
to the mean eddy size of the turbulence.
See also Ellison scale. Since experimental evidence
indicates that the Thorpe scale is nearly
identical to the Ozmidov scale LO, the Thorpe
scale is often considered as the maximum size
of the vertically overturning eddies. See Thorpe
displacement.
thrust fault A dip-slip fault upon which the
deformation is compressional. See reverse fault.
Tibetan Plateau Located to the southwest
of China. Its area is about 200 × 10 4 km 2 , and
average sea level elevation is about 4 km. Since
the Tibetan Plateau is at the middle level of the
troposphere (about 600 hPa level), it strongly
affects the atmospheric circulations by its orographic
thermal and dynamic effects. In the
summer, almost every meteorological observation
element over the Tibetan Plateau has the
most strong diurnal variations in the world; and
cumulus convective activities are very frequent
and active due to the large orographic heating
effects. In the summer, the low levels of the
Tibetan Plateau are a thermal low pressure region,
and the high level at 200 hPa is the south
Asian high, which is maintained by the high
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tidal forces
temperature and high vertical moisture transport
from the lower levels. Such vertical transport is
mainly carried out by the strong and frequent
cumulus convective activities over the plateau.
In contrast, in winter, at low levels they are cold
high pressure systems, and at high levels they
are cold low pressure systems. The opposite
plateau pressure systems in winter and summer
cause the special plateau monsoon. To the atmosphere,
the plateau is a heat source during
both winter and summer; and the atmosphere
over the plateau to the atmosphere around it is
a heat source in summer and a cold source in
winter. The thermal effects of the plateau in the
winter enhance the Hadley circulation over the
plateau; in the summer, they create the monsoon
meridional and zonal circulation systems, which
all come from the ascending air over the plateau
and flow to the east Pacific, northern Africa, and
southern hemisphere. The seasonal change of
the cold and heat source is also an important
factor to cause the seasonal change (jump) of
the east Asian circulations.
tidal bore A translating wave found in coastal
areas that resembles a hydraulic jump. Found at
locations with very large (O(10 m)) tide range.
tidal currents A current that is driven by
pressure gradients within the wave that results
in tidal fluctuations in coastal areas. Often bidirectional
(ebb and flood) in estuaries or rotary
in open water.
tidal delta A deposit of sediments transported
by a combination of waves and tidal currents
at a tidal inlet. Many inlets have both ebb
and flood deltas.
tidal energy dissipation Conversion of work
done to a celestial body by tidal forces into heat
due to the anelastic tidal response of the body.
For example, the total rotational energy of the
Earth–moon system decreases as a result of tidal
energy dissipation, while the angular momentum
is conserved. The rate of lunar tidal energy
dissipation is about 3 × 10 12 W.
tidal forces Differences in the gravitational
force on opposite ends of an extended body
caused by the different distances of those ends
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