Modeling Intrinsic Variability and Connectivity in Shelf and Littoral Circulation
Abstract
We propose research on “Modeling Intrinsic Variability and Connectivity in Shelf and Littoral Circulation” using the Regional Oceanic Modeling System (ROMS) both in idealized flow configurations for process studies and in several realistic simulation situations in support of the planning and interpretation of ONR field measurements. ROMS is well suited as an investigative tool for this oceanic regime. It is widely used in regional simulations of coastal circulations; it has a mature one- and two-way grid-nesting capability that allows for fine-scale calculations of local flow phenomena that are importantly influenced by the larger-scale circulations that comprise the local environment; it utilizes the skillful K-Profile Parameterization (KPP) for the surface and bottom turbulent boundary-layer flux profiles; and it incorporates the surface wave-current interaction theoretical framework based on averaging over the primary phase oscillations of the waves that represents the important role of Stokes drift in providing wave-induced Coriolis and vortex forces and material advection of scalar concentrations, in addition to additional wave-related parameterizations for depth-induced breaking (surf) and enhanced interior turbulent mixing. The research directions are to investigate submesoscale fronts, density filaments, topographic wakes, rip currents, and coherent vortices on small horizontal scales ( 10s-1000s m) with full wave-current interaction in the context of continental-shelf flows and their approach to the shoreline. A particular focus is on how the boundary layer turbulence interacts with submesoscale surface-layer frontogenesis and how bottom-drag generates vorticity that separates into unstable wakes. Two developmental directions are to further incorporate non-hydrostatic dynamics into ROMS for very fine-scale flows where parameterizations reach their limits of validity and implement downscale shelf- and surf-domain nesting using operational HYbrid Coordinate Ocean Model (HYCOM) for the boundary conditions. The modeling approach involves coupling to surface gravity wave dynamics, both in simplified, “spectrum-peak” ray-theory models and in the operational full-spectrum models, SimulatingWAves Nearshore (SWAN) andWave-Watch III (WW3), to capture the Doppler-shifting refraction effect of currents on the waves. The primary hypotheses are (1) the shelf and littoral zone manifests high intrinsic variability beyond the wind-, tide- and waveforced flows; (2) surf eddies and submesoscale shelf eddies have intermittent strong interactions with each other; and (3) these eddies play a dominant role in setting the rates of material transport across and along bathymetric gradients, as well as vertically through the pycnocline. The realistic simulations will be performed for several wind and wave regimes at sites along the U.S. West Coast and the northern Gulf of Mexico including the selected sites for ONR field experiments. A particular issue is the relative importance of littoral current instability and (stochastic) variability of incident surface waves in instigating surf eddy activity; this topic will be collaboratively investigated with Prof. Falk Feddersen (Scripps). Both surf eddies and submesoscale shelf eddies are relatively unexplored phenomena, and the proposed theoretical and computational investigations will lead to new phenomenological discoveries, as well as guidance and interpretation for future ONR field studies. 2.0 Requirements: 1.1 The PI shall perform realistic simulations using ROMS for several wind and wave regimes along the U.S. West Coast and northern Gulf of Mexico. 1.2 The PI shall conduct theoretical and computational studies of surf eddies and submesoscale shelf eddies. 3.0 Deliverables: Reports will be submitted on an annual basis, and a final report will be submitted upon the completion of the award. 1
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512645
Entities
People
- James C. McWilliams
Organizations
- Office of Naval Research
- United States Navy
- University of California, Los Angeles