Internal tide variability off Central California: multiple sources, seasonality, and eddying background

Two moorings deployed for 75 days in 2019 and long-term satellite altimetry data re- 1veal a spatially complex and temporally variable internal tidal field at the 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 M2 with 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.