Coastal Ocean Modeling Quiz

Assessing the Role of Open Boundary Conditions and Tidal Forcing in Coastal Ocean Models

• Coastal ocean modeling has a persisting problem with adequate open boundary conditions, especially in the presence of complex bathymetric features commonly found in shelf seas.
• Ocean models with horizontal resolutions of O(1km) can generate submesoscale current variability not captured by coarser regional models which resolve mesoscale flows approximately in geostrophic and thermal-wind balance.
• Higher-resolution systems will provide analyses with enhanced spatial detail but may be less skillful at predicting the evolution of mesoscale eddies.
• The study aims to assess the role of open boundary conditions, tidal forcing, and tide filtering techniques in a coastal ocean model using a split-explicit time marching scheme with horizontal resolutions of O(1km) and its effect on coastal sea level dynamics and ocean currents.
• Numerical experiments have been performed using the Regional Ocean Modeling System (ROMS) with different uniform horizontal resolutions: 3.6km, 1.2km, and 740m.
• Initial and lateral boundary conditions are derived from the U.S. Naval Oceanographic Office (NAVOCEANO) operational AmSeas model forecast, a 3.6-km resolution application of the regional Navy Coastal Ocean Model (NCOM) that encompasses the Gulf of Mexico and Caribbean Sea.
• Meteorological conditions are interpolated from the Navy’s Coastal Ocean-Atmosphere Mesoscale Prediction System (COAMPS) model with the exception of surface stresses, which are computed from a 2-km application of the Weather Research and Forecasting (WRF) model used by National Center for Environmental Protection’s (NCEP) National Digital Forecast Database (NDFD).
• Tidal variability is imposed in two ways: 1) by specifying the time evolution of sea level at the open boundaries and 2) spectrally by specifying the harmonic phases and amplitudes from the TPXO global inverse tide solutions at the boundaries.
• Sub-tidal low frequency conditions are imposed by filtering high frequencies out of the regional NCOM solution.
• Tide signals are then reconstructed and removed from the open boundary condition’s (OBC’s) in 2 ways: 1) using Rich Pawlowicz’s t_tide package (i.e., classic harmonic analysis) and 2) with traditional low-pass filters.
• The spectral analysis provides a comprehensive characterization of the response in coastal sea level dynamics, which is difficult to elucidate in the time domain.
• The grid sensitivity analysis shows significant reduction of error when increasing the resolution from 3.6km to 1.2km, but no further improvement is found at higher resolution. Power spectra show that further increasing the resolution yields better agreement for higher frequencies but no significant reduction in error.

Test your knowledge on coastal ocean modeling with this quiz! Learn about the persistent problem of open boundary conditions and the role of tidal forcing in coastal ocean models. Discover the impact of higher-resolution systems on predicting ocean currents and the evolution of mesoscale eddies. Assess your understanding of the study's numerical experiments using the Regional Ocean Modeling System (ROMS) with different uniform horizontal resolutions. Take this quiz now and enhance your understanding of coastal sea level dynamics and ocean currents!