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Dr. Nirnimesh Kumar (University of Washington)

Title: Semi-diurnal Internal Tidal Processes in the Santa Maria Basin
Host: IAHR student chapter/Kelly Kibler

Dr. Kumar an Assistant Professor at the Department of Civil and Environmental Engineering, Univ. of Washington. Before this he was a postdoctoral scholar in the Integrative Oceanography Division at the Scripps Institution of Oceanography, UC San Diego. He conducted his doctoral research in the Coastal Processes and Sediment Dynamics lab at the Earth and Ocean Sciences department of the University of South Carolina, Columbia. His broad research interest is in Coastal Physical Oceanography with focus on surf zone and inner-shelf processes, wave-current interaction and sediment transport. He uses a combination of field observations and suite of numerical models to conduct research.


The Santa Maria Basin (SMB) is a part of the Eastern Pacific coastal ocean extending from Pt. Arguello to Pt. Buchon, CA. This region is subjected to strong internal tidal variability leading to complex three-dimensional circulation patterns, density evolution on synoptic and shorter time scales, and material exchange. Previous studies in this region indicate that during summer the semidiurnal internal tidal activity onshore of the shelf break is from internal tidal generation on the continental slope at water depths of h=1000-3000m, with no local generation occurring at the shelf break. Furthermore, from the shelf-break to the mid-shelf, about 50% of internal tidal energy fluxes are phase-locked to astronomical tides (coherent), while the other 50% is incoherent. However, the length scales over which semidiurnal internal tidal energetics vary within the SMB, along with temporal variability on seasonal and longer time scales, are not yet known.

Here, we use the Regional Ocean Modeling System to simulate semidiurnal internal tidal dynamics in the SMB. The model grid with varying horizontal resolution optimally resolves the coastal and inner-shelf dynamics. Model hindcasts for 2017 are validated against velocity and temperature measurements from the mid- and inner-shelf observations from September to October, 2017. At 50m water depth, modeled internal tidal energy fluxes are stronger offshore of Pt. Sal and Pt. Purisima but decrease north of Pt. Sal. Energy fluxes strongly dissipate from 50 to 30m, indicating a region of strong vertical mixing, which has implications for stratification and cross-shore circulation. The year long simulation is also used to investigate seasonal variability in internal tidal generation pattern, and transition from coherent to incoherent fluxes. The dependency of the seasonal variability in internal tidal energetics to changes in local stratification, wind-driven circulation, submesoscale eddy activity, and nonlinear interactions are investigated. Funded by the Office of Naval Research.