NearCoM: NEARSHORE-POM Circulation Module

Authors:

P.A. Newberger, J.S. Allen
College of Oceanic and Atmospheric Sciences,
Oregon State University, Corvallis

Contact information:

Documentation:
Allen, J. S., Newberger, P. A., 2005, ``Development and verification of a comprehensive community model for physical processes in the nearshore ocean, final technical report, OSU component" (pdf)

Overview:

The basic Princeton Ocean model (POM) is well documented in the POM user's guide available from http://www.aos.Princeton.EDU/WWWPUBLIC/htdocs.pom/. POM is a numerical, finite-difference model for the hydrostatic primitive equations that has been widely applied to coastal and global ocean studies. All of the functionality of POM has been retained in the nearshore version. The standard model includes Coriolis force terms, which may be set to zero, and capabilities for forcing by wind stress and surface heat flux. The effect of stratification by temperature and salinity is included. The Mellor-Yamada level 2.5 turbulence closure is used to determine the vertical mixing of momentum and the scalar fields. Other two-equation turbulent closure models, e.g. k-epsilon, can be, and have been, readily implemented when prefered. The model uses an orthogonal curvilinear grid in the horizontal and a terrain-following, sigma coordinate system in the vertical. The Nearshore POM circulation has additional forcing parameterized from the wave field provided by the wave module. Changes in the surface boundary conditions of the mean vertical velocity have been made to account for the Eulerian mass flux of the waves. The surface boundary conditions of the turbulent kinetic energy equation have been modified to reflect increase in turbulence under breaking waves. A wave-current bottom boundary layer model is embedded to provide the increased bottom stress in the presence of waves.

Use and initialization of the module:

A subroutine, setup.f, must be modified to define the situation to be modeled. Sample setup subroutines and, when needed, data files to compute the standard POM test cases (no wave forcing) and to compute a two-dimensional vertical slice with wave forcing in the nearshore are included. The module requires an input file, pom.input, in which all parameters and input files needed for the problem are specified. The forcing of wave averaged flow in a fully three-dimensional model is a current research problem. The subroutine force.f calculates the forcing from the output of the wave module based on present understanding. This subroutine must be modified as progress is made on the formulation of the wave forcing problem. A discussion of all parameters in the pom.input file and a complete discussion of setup.f are included in the Nearshore POM documentation. Required inputs include both those that reflect the physics of the parametrized quantities such as surface and bottom roughness lengths and those that are primarily related to the numerics of the model such as vertical grid spacing. Some guidelines for selection of parameters are included in the documentation. A fully three-dimensional model requires a significant amount of computation at each time step. It is assumed that this circulation model will be used primarily for scientific research purposes.

Variables provided by the circulation module:

Three-dimensional (3D) and depth integrated velocity fields, 3D fields of potential density, or temperature, salinity and density, 3D fields of turbulent kinetic energy, 3D and depth integrated momentum balances, wave-averaged surface elevation, bottom stress as seen by the wave-averaged current above the wave boundary layer. Time series of these fields at desired locations can also be saved.

Variables required by the circulation module:

Undisturbed water depth (from the master program, possibly updated by the sediment module). Wave and roller radiation stress type forcing capable of being partitioned into surface stress and depth-dependent terms, wave and roller mass flux, wave height, near bottom orbital velocity, wave number, celerity, group speed, wave direction (from the wave module).