التفاصيل البيبلوغرافية
| العنوان: |
Dynamics of Tidal Effects on Coastal Upwelling Circulation Over Variable Shelves in the Northern South China Sea. |
| المؤلفون: |
Lin, Shangfei, Gan, Jianping |
| المصدر: |
Journal of Geophysical Research. Oceans; Sep2024, Vol. 129 Issue 9, p1-21, 21p |
| مصطلحات موضوعية: |
TIDAL currents, UPWELLING (Oceanography), SEAWATER, BOUNDARY layer (Aerodynamics), SEA level |
| مستخلص: |
The impact of tidal forcing on the complex three‐dimensional (3D) wind‐driven upwelling dynamics over highly variable shelves is important but remains unclear. Combining field and satellite observations and a high‐resolution numerical model, we investigated tidal effects on the 3D transport and dynamics of the wind‐driven upwelling circulation in the northern South China Sea. Our results showed that tides weaken (strengthen) the subtidal along‐isobath and cross‐isobath transports in the inner (outer) shelf, primarily by modulating the corresponding cross‐isobath and along‐isobath pressure gradients. The tidally induced geostrophic adjustment is predominantly contributed by its barotropic effect due to sea level gradients above the bottom boundary layer (BBL) in both the inner and outer shelves. The baroclinic process, caused by tidally modulated density gradients, counteracts the barotropic effect and dominates the intensified onshore flow within a thickened BBL from the outer to middle shelves, together with the enhanced bottom stress. Based on the vorticity dynamic, this baroclinic process leads to an amplified joint effect of baroclinicity and relief over the steep shelf that strengthens tidally modulated along‐isobath pressure gradients. While tidally enhanced bottom stress curl can be essential in the inner shelf. The intensity of tidal modulation varies across different shelves, depending on tidal strength and bottom topography. The subtidal bottom onshore transport can increase by sevenfold when strong tidal currents persist over a steep outer shelf. This comprehensive study unveiled the dynamics of tidal effects on the upwelling and the importance of an interlinked tidal‐subtidal system over complex shelf topography. Plain Language Summary: Our study explored how tides affect the upward movement of deep ocean water, known as upwelling, in the northern South China Sea. Model results indicated that tidal currents interact with the varying topography producing tidal residual currents that weaken the wind‐driven upwelling circulation in the inner shelf while promote it in the outer shelf. Meanwhile, tidal surface elevations reduce the efficiency of the wind‐driven upwelling current, further reducing the upwelling in the inner shelf. These tidal effects primarily arise from the barotropic effect, driven by changes in sea level gradients, and offset by the baroclinic process, influenced by density gradients. Consequently, tides cause higher water temperatures in the inner shelf but facilitate the outcrop of cold water in the steep outer shelf, which is also evidenced by field and satellite observations. These tidal impacts vary across different shelves, depending on the tidal strength and bottom topography. Notably, the bottom onshore transport exhibits a remarkable increase of sevenfold across the steep outer shelf in regions with strong tidal currents. Our comprehensive research highlighted the critical role of tides in shaping upwelling circulation and revealed the intricate dynamics of the coupled tidal‐subtidal coastal system. Key Points: Tides weaken (enhance) along/cross‐isobath transports in the inner (outer) shelf due to residual currents and tidal‐subtidal interactionTidal modulation on upwelling is dominated by the geostrophic adjustment through competitive barotropic and baroclinic processesTidally enhanced baroclinic along‐isobath pressure gradients and bottom stress strengthen the bottom onshore transport [ABSTRACT FROM AUTHOR] |
|
Copyright of Journal of Geophysical Research. Oceans is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) |
| قاعدة البيانات: |
Complementary Index |