 |
| Titel |
Characterizing the nonlinear internal wave climate in the northeastern South China Sea |
| VerfasserIn |
S. R. Ramp, Y. J. Yang, F. L. Bahr |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1023-5809
|
| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 17, no. 5 ; Nr. 17, no. 5 (2010-09-29), S.481-498 |
| Datensatznummer |
250013727
|
| Publikation (Nr.) |
 copernicus.org/npg-17-481-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
Four oceanographic moorings were deployed in the South China Sea from April
2005 to June 2006 along a transect extending from the Batanes Province,
Philippines in the Luzon Strait to just north of Dong-Sha Island on the
Chinese continental slope. The purpose of the array was to observe and track
large-amplitude nonlinear internal waves (NIWs) from generation to shoaling
over the course of one full year. The basin and slope moorings observed
velocity, temperature (T) and salinity (S) at 1–3 min intervals to
observe the waves without aliasing. The Luzon mooring observed velocity at
15 min and T and S at 3 min, primarily to resolve the tidal forcing in
the strait.
The observed waves travelled WNW towards 282–288 degrees with little
variation. They were predominantly mode-1 waves with orbital velocities
exceeding 100 cm s−1 and thermal displacements exceeding 100 m.
Consistent with earlier authors, two types of waves were observed: the
a-waves arrived diurnally and had a rank-ordered packet structure. The
b-waves arrived in between, about an hour later each day similar to the
pattern of the semi-diurnal tide. The b-waves were weaker than the a-waves,
usually consisted of just one large wave, and were often absent in the deep
basin, appearing as NIW only upon reaching the continental slope. The
propagation speed of both types of waves was 323±31 cm s−1 in the
deep basin and 222±18 cm s−1 over the continental slope. These
speeds were 11–20% faster than the theoretical mode-1 wave speeds for the
observed stratification, roughly consistent with the additional contribution
from the nonlinear wave amplitude. The observed waves were clustered around
the time of the spring tide at the presumed generation site in the Luzon
Strait, and no waves were observed at neap tide. A remarkable feature was the
distinct lack of waves during the winter months, December 2005 through
February 2006.
Most of the features of the wave arrivals can be explained by the tidal
variability in the Luzon Strait. The near-bottom tidal currents in the Luzon
Strait were characterized by a large fortnightly envelope, large diurnal
inequality, and stronger ebb (towards the Pacific) than flood tides. Within
about ±4 days of spring tide, when currents exceeded 71 cm s−1,
the ebb tides generated high-frequency motions immediately that evolved into
well-developed NIWs by the time they reached mooring B1 in the deep basin.
These waves formed diurnally and correspond to the a-waves described by
previous authors. Also near spring tide, the weaker flood tides formed NIWs
which took longer/further to form, usually not until they reached mooring S7
on the upper continental slope. These waves tracked the semidiurnal tide and
correspond to the b-waves described by previous authors. These patterns were
consistent from March to November. During December–February, the structure
of the barotropic tide was unchanged, so the lack of waves during this time
is attributed to the deep surface mixed layer and weaker stratification along
the propagation path in winter. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|