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Abstract Two moorings deployed for 75 days in 2019 and long‐term satellite altimetry data reveal a spatially complex and temporally variable internal tidal field at the Surface Water and Ocean Topography (SWOT) Cal/Val site off central California due to the interference of multiple seasonally‐variable sources. These two data sets offer complementary insights into the variability of internal tides in various time scales. The in situ measurements capture variations occurring from days to months, revealing ∼45% coherent tides. The north mooring displays stronger mode‐1 M2with an amplitude of ∼5.1 mm and exhibits distinct time‐varying energy and modal partitioning compared to the south mooring, which is only 30‐km away. The 27‐year altimetry data unveils the mean and seasonal variations of internal tides. The results indicate that the complex internal tidal field is attributed to multiple sources and seasonality. Mode‐1 tides primarily originate from the Mendocino Ridge and the 36.5–37.5°N California continental slope, while mode‐2 tides are generated by local seamounts and Monterey Bay. Seasonality is evident for mode‐1 waves from three directions. The highest variability of energy flux is found in the westward waves (±22%), while the lowest is in the southward waves (±13%). The large variability observed from the moorings cannot be solely explained by seasonality; additional factors like mesoscale eddies also play a role. This study emphasizes the importance of incorporating the seasonality and spatial variability of internal tides for the SWOT internal tidal correction, particularly in regions characterized by multiple tidal sources.
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Southward Internal Tides in the Northeastern South China Sea
Abstract The M2internal tides in the northeastern South China Sea are studied using satellite altimeter data from 1992–2018. By an improved mapping technique that combines plane wave analysis and two‐dimensional spatial filtering, multiple internal tides are separately extracted with weak internal tides becoming detectable. The satellite results reveal for the first time a 300‐km‐long southward M2internal tidal beam in the northeastern South China Sea. The generation source is on the steep continental slope at the southern entrance to the Taiwan Strait. It ranges from 118–120°E along 22°N. Combining satellite‐observed internal solitary waves and internal tides, it is found that the onshore radiation evolves into nonlinear solitary waves and the offshore radiation in the form of linear internal tides. Based on the 26‐year‐coherent satellite results, the integrated southward energy flux is 0.18 GW, about 10% of the westward energy flux from the Luzon Strait. In the northeastern South China Sea, the westward and southward internal tides form a multiwave interference field, which features significant spatial variations in the magnitude and direction of energy flux. Further analyses reveal that the steep continental slope radiates southward semidiurnal M2and S2internal tides, but not diurnal K1and O1internal tides.
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- Award ID(s):
- 1634041
- PAR ID:
- 10375138
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 125
- Issue:
- 11
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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