The Regional Oceanic Modeling System (ROMS) is a circulation code
adaptable to different simulation domains ranging from basins to
estuaries. With suitable bathymetery, initialization, and forcing,
its goal is realism falsifiable by measurements. The ocean is highly
variable and heterogeneous, and the scope for novel modeling
applications is great.

Its inception was an invitation by Scott Harper of the U.S. Office of
Naval Research to Dale Haidvogel and Jim McWilliams to create a new
simulation model. The primary focus was algorithmic. ROMS was
innovative with respect to its combination of an air-sea free surface,
a terrain-following vertical coordinate, higher-order diffusive
advection, pressure-gradient calculation, barotropic-baroclinic
mode splitting, higher-resolution nested subdomains, and time
stepping. These elements have endured with continuing model
evolution.

ROMS is based on the incomressible, hydrostatic (Primitive) equations
that are appropriate to anisotropic currents with a horizontal scale
greater than, say, 1 km. Recent extensions are made to
non-hydrostatic dynamics for smaller-scale currents, even down to the
practices of Large-Eddy Simulations, at least in preliminary
simulations. Its subgrid-scale components are deliberately minimal,
with explicit vertical mixing schemes only in the surface and bottom
boundary layers and in interior regions with small Richardson number
(weak or negative stratification and strong vertical shear); these
parameterizations are likely to be adapted as model applications move
toward grids with a horizontal resolution dx less than 10 m.

As a physical model it provides a foundation for various couplings
with other modeling systems: oceanic biogeochemistry, sediment
movement, surface gravity waves, data assimilation, and atmospheric
circulation and chemistry.

ROMS is widely used by the sub-global, sub-climate oceanic modeling
community. It now has multiple distribution homes, and the UCLA group
continues to be a principal innovator and user.

The UCLA ROMS code is open source, with a distribution at
https://github.com/CESR-lab/ucla-roms/. We are a small group of
scientists whose primary goal is scientific publications about
phenomenological discovery and dynamical interpretation. Hence, our
ability to provide training and trouble-shooting for a wider audience
is limited, although we aspire to be helpful. Reports of code errors
are welcome, of course.

A list is appended of the actively collaborating group members at UCLA
and elsewhere.

Also appended is an illustrative animation of the surface current
speed in a realistic Pacific Ocean simulation with dx = 6 km and
high-frequency surface and tidal forcing. The duration is half a
year. Click to enlarge in a new window.