Publication Date:
2022-05-25
Description:
Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1157-1181, doi:10.1109/JOE.2004.840839.
Description:
A moored array of current, temperature, conductivity,
and pressure sensors was deployed across the Chinese
continental shelf and slope in support of the Asian Seas International
Acoustics Experiment. The goal of the observations was to
quantify the water column variability in order to understand the
along- and across-shore low-frequency acoustic propagation in
shallow water. The moorings were deployed from April 21–May
19, 2001 and sampled at 1–5 min intervals to capture the full range
of temporal variability without aliasing the internal wave field.
The dominant oceanographic signal by far was in fact the highly
nonlinear internal waves (or solitons) which were generated near
the Batan Islands in the Luzon Strait and propagated 485 km
across deep water to the observation region. Dubbed trans-basin
waves, to distinguish them from other, smaller nonlinear waves
generated locally near the shelf break, these waves had amplitudes
ranging from 29 to greater than 140 m and were among the largest
such waves ever observed in the world’s oceans. The waves arrived
at the most offshore mooring in two clusters lasting 7–8 days each
separated by five days when no waves were observed.Within each
cluster, two types of waves arrived which have been named type-a
and type-b. The type-a waves had greater amplitude than the
type-b waves and arrived with remarkable regularity at the same
time each day, 24 h apart. The type-b waves were weaker than
the type-a waves, arrived an hour later each day, and generally
consisted of a single soliton growing out of the center of the
wave packet. Comparison with modeled barotropic tides from
the generation region revealed that: 1) The two clusters were
generated around the time of the spring tides in the Luzon strait;
and 2) The type-a waves were generated on the strong side of the
diurnal inequality while the type-b waves were generated on the
weaker beat. The position of the Kuroshio intrusion into the Luzon
Strait may modulate the strength of the waves being produced. As
the waves shoaled, the huge lead solitons first split into two solitons
then merged together into a broad region of thermocline depression
at depths less than 120 m. Elevation waves sprang up behind
them as they continued to propagate onshore. The elevation waves
also grew out of regions where the locally-generated internal tide
forced the main thermocline down near the bottom. The “critical point” where the upper and lower layers were equal was a good
indicator of when the depression or elevation waves would form,
however this was not a static point, but rather varied in both space
and time according to the presence or absence of the internal tides
and the incoming trans-basin waves themselves.
Description:
The planning,
execution, and analysis of this work was supported by the U.S. Office of Naval
Research Ocean Acoustics and Physical Oceanography Programs. Significant
funding contributions were also made by the National Science Council of
Taiwan.
Keywords:
Baroclinic tides
;
Nonlinear internal waves
;
Ocean currents
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
2809125 bytes
Format:
application/pdf
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