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Abstract:
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Measurements of ocean currents were made by the
author in the Western Mediterranean Sea at five depths
for two months during early 1969. In terms of the dominant
and persistent presence of inertial oscillations,
circularly polarized currents having periods of a half
pendulum day, the data are among the most striking
ever collected.
Two contemporary theories have been adapted for
interpretation of this data. On the basis of a ray or
short-wave-length theory, energy arriving at the observing
site is found to fall into two categories, that
making direct arrival from the, surface where it is assumed
to have been generated, and that which undergoes
one or more reflections. To the extent that the
former dominates, it is found that the Algerian Coast
about 130 km. to the south would cast a shadow to the
north, the precise shape of which would be highly
dependent on small variations in frequency. The nature
of this frequency dependence implies a gradual increase
in frequency with depth at the observing latitude.
Although the data show a measurable shift (about 3%)
towards higher frequencies, which is roughly the
required amount, the lack of progressive frequency
change with depth does not support the shadow
hypothesis.
In addition, the data is interpreted in terms of
normal mode theory, where the nearby coast is seen to
force a discrete modal structure to the solutions.
The observed variation of current phase with depth
indicates that a single internal mode dominates over
a large portion of the data, while variations of both
current amplitude and phase with depth are consistent
this being the third internal vertical mode. Existence
of a normal mode is also consistent with the long time,
on the order of three weeks, for which the oscillations
were observed to persist and with the dimensions of
the Mediterranean Basin. |