Coastal Semidiurnal Internal Tidal Incoherence in the Santa Maria Basin, California: Observations and Model Simulations. Issue 7 (24th July 2019)

• Record Type: Journal Article
• Authors: Kumar, Nirnimesh; Suanda, Sutara H.; Colosi, John A.; Haas, Kevin; Di Lorenzo, Emanuele; Miller, Arthur J.; Edwards, Christopher A.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 7(2019)
• Page Start: 5158
• Page End: 5179
• Publication Date: 2019-07-24
• Subjects: internal waves -- midshelf -- ROMS -- incoherence -- central California -- inner shelf; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2018JC014891
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: A series of five realistic, nested, hydrostatic numerical ocean model simulations are used to study semidiurnal internal tide generation and propagation from the continental slope, through the shelf break and to the midshelf adjacent to Point Sal, CA. The statistics of modeled temperature and horizontal velocity fluctuations are compared to midshelf observations (30‐ to 50‐m water depth). Time‐ and frequency‐domain methods are used to decompose internal tides into components that are coherent and incoherent with the barotropic tide, and the incoherence fraction is 0.5–0.7 at the midshelf locations in both the realistic model and observations. In contrast, the incoherence fraction is at the most 0.45 for a simulation with idealized stratification, and neither atmospheric forcing nor mesoscale currents. Negligible conversion from barotropic to baroclinic energy occurs at the local shelf break. Instead, the dominant internal tide energy sources are regions of small‐scale near‐critical to supercritical bathymetry on the Santa Lucia escarpment (1, 000–3, 000 m), 70–80 km from the continental shelf. Near the generation region, semidiurnal baroclinic energy is primarily coherent and rapidly decays adjacent to the shelf break. In the realistically forced model, incoherent energy is less than 10% in the generation region, with a steady increase in incoherence fraction from the continental slope to the midshelf. Backward ray tracing from the midshelf to the Santa Lucia escarpment identifies multiple energy pathways potentially leading to spatial interference. As internal tides shoal on the predominantly subcritical slope/shelf system, temporally variable stratification and Doppler shifting from mesoscale and submesoscale features appear equally important in leading to the loss of coherence. Key Points: Semidiurnal internal tides are primarily incoherent on the continental shelf of the Santa Maria Basin Barotropic to baroclinic conversion occurs at multiple locations, 70–80 km from midshelf measurement locations Shelf internal tide incoherence is strongly influenced by variable stratification and mesoscale currents