178
5. Tides
shallow sea where frictional effects on the tidal motion are significant. As a
result, the amphidromic points move away from the source of the tidal energy,
which approaches from the Atlantic Ocean from the north and moves counterclockwise around the basin. Due to the effect of friction, the amphidromic
points in the North Sea are shifted eastward. Hence, the east coast of Britain
has high tides, because of the larger distance from the amphidromic points,
while the eastern regions of the North Sea experience smaller tides. In the
English Channel, the amphidromic point is situated in the south of England.
The tidal waves in the English Channel move in the same direction along both
coasts of the Channel. An example of an amphidromic system in the Southern
Hemisphere, on the north-west coast of Australia is shown in Fig. 5.15.
5.4 Harmonic Analysis and Prediction of Tides
5.4.1 Prediction of Tides
Modern numerical hydrodynamic models provide accurate prediction of tides
in deep water. However, for prediction of tides on the shelf and close to coasts,
these models are not yet developed to the stage where they are of practical
use at arbitrary points. In such situations, tidal predictions are based on the
observations of tides at the desired locations for very long periods of time.
Using the periods of the basic tide producing forces (tidal constituents), we
can predict the tide at a given point by harmonic analysis, as was described in
Chap. 4. As many as 390 tidal constituents have been identified, however not
all of these are used in practical calculations. The most important have been
listed in Table 5.2.
Hence, for the given time series of duration T, the representation of tides
becomes:
n=N
((t) = L cncos(wnt + 'Pn),
(5.30)
n=1
in which Wn = 27rn/T; T is the period of observation; N is the number of
constituents involved; Cn and 'Pn are the amplitudes and phases of particular
constituents, respectively. For many points around the Earth, the amplitudes
and phases of tidal constituents have been calculated and predicted tides are
listed in tide tables. An example of such predictions is shown in Fig. 5.16 for
the Mackay area on the east coast of Australia. The prediction is based on
long-term observation and 22 constituents were used in the harmonic analysis.
It was shown by Defant (1961) that the nature of the tide at the particular
point can be characterized by the form number F, which is the ratio of the
sum of the amplitudes of the major constituents:
(5.31)
5. Tides
shallow sea where frictional effects on the tidal motion are significant. As a
result, the amphidromic points move away from the source of the tidal energy,
which approaches from the Atlantic Ocean from the north and moves counterclockwise around the basin. Due to the effect of friction, the amphidromic
points in the North Sea are shifted eastward. Hence, the east coast of Britain
has high tides, because of the larger distance from the amphidromic points,
while the eastern regions of the North Sea experience smaller tides. In the
English Channel, the amphidromic point is situated in the south of England.
The tidal waves in the English Channel move in the same direction along both
coasts of the Channel. An example of an amphidromic system in the Southern
Hemisphere, on the north-west coast of Australia is shown in Fig. 5.15.
5.4 Harmonic Analysis and Prediction of Tides
5.4.1 Prediction of Tides
Modern numerical hydrodynamic models provide accurate prediction of tides
in deep water. However, for prediction of tides on the shelf and close to coasts,
these models are not yet developed to the stage where they are of practical
use at arbitrary points. In such situations, tidal predictions are based on the
observations of tides at the desired locations for very long periods of time.
Using the periods of the basic tide producing forces (tidal constituents), we
can predict the tide at a given point by harmonic analysis, as was described in
Chap. 4. As many as 390 tidal constituents have been identified, however not
all of these are used in practical calculations. The most important have been
listed in Table 5.2.
Hence, for the given time series of duration T, the representation of tides
becomes:
n=N
((t) = L cncos(wnt + 'Pn),
(5.30)
n=1
in which Wn = 27rn/T; T is the period of observation; N is the number of
constituents involved; Cn and 'Pn are the amplitudes and phases of particular
constituents, respectively. For many points around the Earth, the amplitudes
and phases of tidal constituents have been calculated and predicted tides are
listed in tide tables. An example of such predictions is shown in Fig. 5.16 for
the Mackay area on the east coast of Australia. The prediction is based on
long-term observation and 22 constituents were used in the harmonic analysis.
It was shown by Defant (1961) that the nature of the tide at the particular
point can be characterized by the form number F, which is the ratio of the
sum of the amplitudes of the major constituents:
(5.31)