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Seventy‐five days of sea surface height measurements made by the Surface Water and Ocean Topography (SWOT) mission from 7 September to 21 November 2023 are used to explore SWOT's capability of observing internal tides. Mode‐1 internal tides are mapped by our updated mapping technique. SWOT‐75d represents a 75‐day instantaneous model. Nadir‐30y is constructed using 30 years of nadir altimetry data from 1993 to 2022 and represents a climate normal. The nadir altimetry data in 2023 are used for model evaluation. Despite its large errors, SWOT‐75d reveals the basic features of the global mode‐1 internal tide field, and causes positive variance reduction in regions of strong internal tides. Nadir‐30y performs better overall, but SWOT‐75d performs better in the tropical South Atlantic Ocean, the central North Pacific Ocean, and the Melanesian region. Evaluation using seasonally subsetted altimetry data reveals that internal tides have significant temporal variations. SWOT‐75d performs the best in fall, because the model is constructed using data largely in fall. SWOT‐75d has large phase anomalies, which are spatially smoothed and used to adjust the phases in Nadir‐30y. The phase‐adjusted model can better make internal tide correction for SWOT and its performance is improved by 20%. Our results demonstrate that (a) mode‐1 internal tides can be extracted from 75 days of SWOT data by our mapping technique, and (b) the instantaneous internal tide model can be used to improve internal tide correction for SWOT.
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Internal Tide Variability Off Central California: Multiple Sources, Seasonality, and Eddying Background
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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- PAR ID:
- 10532129
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 129
- Issue:
- 8
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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